BEN MC GEE · Mantle dynamics have long been considered to influence the topography and mechanics...
Transcript of BEN MC GEE · Mantle dynamics have long been considered to influence the topography and mechanics...
Supercontinents and Glaciation: a perspective from western Gondwana
B E N M C G E E
Geology and GeophysicsEarth and Environmental Sciences
The University of Adelaideand
The University of São Paulo
July 2013
Thesis Author Statement
I, Ben McGee, certify that this work contains no material which has been accepted for the award of any other degree or diploma in any university or other tertiary institution, and, to the best of my knowledge and belief, contains no material previously published or written by another person, except where due reference has been made in the text.
I give consent to this copy of my thesis when deposited in the University Library, being made available for loan and photocopying, subject to the provisions of the Copyright Act 1968.
The author acknowledges that copyright of published works contained within this thesis (as listed in “Pub-lications Arising From This Thesis”) resides with the copyright holder(s) of those works.
I also give permission for the digital version of my thesis to be made available on the web, via the Uni-versity’s digital research repository, the Library catalogue, and also through web search engines, unless permission has been granted by the University to restrict access for a period of time.
Ben McGee Date
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Table of ContentsThesis Abstract v
Publications Arising From This Thesis vii
Thesis Outline
Author Contribution Statement
Chapter 1: Cryogenian rift-related magmatism and sedimentation: 3 South-western Congo Craton, Namibia.
Introduction 3 Regional Geology 4 Pre-Chuos sedimentation on the southern margin of the 4 Congo Craton The Toekems Sub-basin 6 Analytical Methods 7 U-Pb geochronology 7 Results 7 Stratigraphy and field relationships 7 Lonestones 9 Geochronology 10 Discussion 14 Timing and origin of the Toekems Sub-basin 15 Implications for the age of Chuos glaciation 16 Conclusion 17 References 17
Chapter 2: G’day Gondwana - the final accretion of a supercontinent: 21 U-Pb ages from the post-orogenic São Vicente Granite, northern Paraguay Belt, Brazil Introduction 21 Regional setting 22 Analytical methods 23 U-Pb geochronology 23 Age estimates 24 Discussion: crystallisation age of the São Vicente Granite 24 References 26
Chapter 3: A glacially incised canyon in Brazil: Further evidence for 31 mid-Ediacaran glaciation?
Introduction 31 Regional setting 31 Measured sections 33 Serra Azul 33 São Sebastião 33 Boa Sorte 33 Discussion and conclusions 33 References cited 38
Chapter 4: The tectonic and palaeoenvironmental significance of the 45 Ediacaran to Cambrian Alto Paraguay Group, Paraguay Belt, Brazil.
Introduction 45 Regional setting 46 Analytical methods 47
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Detrital muscovite 40Ar/39Ar isotopic analysis 47 Measured sections 47 Serra Azul section 47 Boa Sorte section 48 Nobres section 48 40Ar/39Ar isotopic results 51 Discussion 53 Facies variations and relative sea level change exhibited by the Alto 53 Paraguay Group Maximum depositional ages of the Alto Paraguay Group 54 Sources of the Alto Paraguay Group 55 Sedimentary-tectonic model for the formation of the Alto Paraguay 55 Group Conclusions 57 References 57
Chapter 5: Age and Provenance of the Cryogenian to Cambrian 67 passive margin to foreland basin sequence of the northern Paraguay Belt, Brazil.
Introduction 67 Regional setting 67 Analytical methods 69 Zircon U-Pb LA-ICPMS analysis 69 Zircon Hf isotopic analysis 69 Results 69 Zircon U-Pb LA-ICPMS isotopic results 69 Age estimates 69 Zircon Hf isotopic results 70 Discussion 71 U-Pb isotopic age constraints and maximum depositional ages 71 U-Pb and Hafnium isotopic results and correlation with potential 72 source regions Tectonic model and the Paraguay Belt within South America and 73 Gondwana Conclusions 76 References cited 76
Chapter 6: An inconvenient truth: Multiple geomagnetic reversals 115 in the Neoproterozoic–Cambrian Alto Paraguay Group, Amazonian Craton, Brazil. Introduction 115 Geological setting 116 Methods 118 Results 119 Demagnetisations 119 Magnetic mineralogy 120 Magnetic components 121 Discussion 122 Conclusions 126 References 126
Chapter 7: Key outcomes and future research 131
Chapter 8: Sedimentological and provenance response to Cambrian 135closure of the Clymene ocean: The upper Alto Paraguai Group,Paraguay Belt, Brazil
Introduction 135
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Geological setting 137 The upper Alto Paraguai Group 138 Facies associations 138 Tidal and wave influenced marine platform 140 Distal turbidite deposits 141 Prodelta lake 142 Delta front 142 U-Pb age provenance analysis 143 Methodology 143 Results 145 Palaeoflow determination 145 Petrography and tectonic environment 145 Palaeogeography and potential source regions 145 Tectonic-sedimentary model 147 Conclusions 147 References 148
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Thesis AbstractPrecise timing for the formation of the Palaeozoic supercontinent Gondwana has long eluded the
geological community. Early hypotheses postulated that amalgamation occurred in the mid-late Neopro-terozoic via a collision between East and West Gondwana. This idea developed with the identification of discrete collisional events between diverse, relatively small Neoproterozoic continents that amalgamated Gondwana in a piecemeal fashion over 150 million years, with a series of late Ediacaran–Cambrian orogens that represent the final phase of Gondwana amalgamation. A salient feature of the rocks preserving these events in the Neoproterozoic sedimentary record is the preservation of glacial sediments. Significant debate has centred around firstly whether these deposits are in fact glacial and secondly the spatial extent of these glaciations. This thesis addresses these deficits in our knowledge by presenting detailed sedimentology, geochronology, palaeomagnetic results from western Gondwana.
The Cryogenian-aged Toekems Sub-basin in the Damara Belt, Namibia comprises a wedge domi-nantly clastic, glacially influenced sediments. Our field observations and results imply a significant discon-formity beneath the Naauwpoort Volcanics and suggest multi-phase rifting during the breakup of south-western Congo Craton from Rodinia.
The northern Paraguay Belt in South America developed in response to the collision between the Amazonian Craton, the Rio Apa Block, the São Francisco Craton and the Paranapanema Block. The al-leged ‘Brasiliano’ age (~620 Ma) of orogenesis was recently questioned by palaeomagnetic and radioiso-topic ages that indicate the closing stages of orogenesis occurred well into the Cambrian that are believed to mark the suture zone of the Clymene Ocean—interpreted amongst the youngest of the Gondwana amalgamation orogens. The post-orogenic São Vicente Granite provides a long sort after minimum age of 518 ± 4 Ma for orogenesis within the belt, constraining the termination of deformation within the northern Paraguay Belt.
The Alto Paraguay Group, the youngest stratigraphic unit in the northern Paraguay Belt, contains unequivocal evidence for a glacial influence on sedimentation. 40Ar/39Ar detrital muscovite cooling ages from the upper part of the Alto Paraguay Group are as young as 544 ± 7 Ma. When considered with other data presented here, these ages suggest that this package of rocks developed in a mid-Ediacaran glaciation consistent with that expressed in the Gaskiers Formation of Newfoundland, Canada. U/Pb zircon maxi-mum depositional ages from the top of the Alto Paraguay Group indicate that final sedimentation began no earlier than 527 Ma. The εHf signature is consistent with a predominantly Amazonian source until the early-Neoproterozoic at which point the signal becomes significantly more evolved.
new palaeomagnetic data from Alto Paraguay Group represent a secondary magnetisation, likely acquired during regional emplacement of Jurassic basalt. This finding is at odds with recent results that have been used to suggest Amazonia was at low latitudes during the Ediacaran, which has implications for the snowball earth hypothesis and the tectonic evolution of the Paraguay Belt.
These data, when combined with other evidence discussed here, are consistent with an ocean to the east of the present-day Amazonian Craton that didn’t close until the Cambrian.
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McGee, B., Collins, A.S. and Trindade, R.I.F., 2012. G’day Gondwana - the final accretion of a su-percontinent: U-Pb ages from the post-orogenic Sao Vicente Granite, northern Paraguay Belt, Brazil. Gondwana Research 21, 316-322.
Bandeira, J., McGee, B., Nogueira, A.C.R., Collins, A.S. and Trindade, R.I.F., 2012. Closure of the Neo-proterozoic Clymene Ocean: sedimentary and detrital zircon geochronology evidence from the siliciclas-tic upper Alto Paraguai Group, northern Paraguay Belt, Brazil. Gondwana Research.
McGee, B., Halverson, G.P. and Collins, A.S., 2012. Cryogenian rift-related magmatism and sedimenta-tion: South-western Congo Craton, Namibia. Journal of African Earth Sciences 76, 34-49.
McGee, B., Collins, A.S. and Trindade, R.I.F., Accepted. A glacially incised canyon in Brazil: Further evidence for mid-Ediacaran glaciation? The Journal of Geology.
McGee, B., Collins, A.S., Trindade, R.I.F. and Jourdan, F. Under review. The tectonic and palaeoen-vironmental significance of the Ediacaran to Cambrian Alto Paraguay Group, Paraguay Belt, Brazil: Sedimentology and 40Ar/39Ar detrital muscovite provenance. Sedimentology.
McGee, B., Collins, A.S. and Trindade, R.I.F., Under Review. Age and Provenance of the Cyrogenian to Cambrian passive margin to foreland basin sequence of the northern Paraguay Belt, Brazil. Bulletin of the Geological Society of America.
McGee, B., Trindade, R.I.F., Rosaffa, M., Collins, A.S. and Tohver, E., Under review. An inconvenient truth: Multiple geomagnetic reversals in the Neoproterozoic–Cambrian Alto Paraguay Group, Amazo-nian Craton, Brazil. Precambrian Research.
Publications Arising From This Thesis
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Thesis OutlineThe latest Proterozoic and earliest Paleozoic eras beautifully illustrate the complexity and intercon-
nectedness of the interactions between Earth’s systems. Mantle dynamics have long been considered to influence the topography and mechanics of the overlying lithosphere (Mitrovica et al., 1989; Pysklywec and Mitrovica, 1997). The impact of ‘mantle avalanches’ have been suggested to play a causal role in the supercontinent cycle (Condie, 1998; Li et al., 2008) – by initiating superplume development – cited as one potential cause for the break-up of Rodinia (Frimmel et al., 2001; Li et al., 2008; Li et al., 1999). The frag-mentation of this supercontinent provided the building blocks for its successor Gondwana.
Undeniably, these deep processes began to effect surface processes, irrevocably changing the Earth to its current biologically rich/diverse state. Increased heat transfer, afforded by the superheated plume head (Campbell and Davies, 2006), enhanced hydrothermal activity in the oceans – indicated by Sr isotopes (Melezhiik et al., 2001) – resulting in increased leaching of metals, capturing large amounts of oxygen, stratifying the ocean and depositing vast banded iron formations (Kaufman et al., 1991) after a hiatus for some 1000 million years. Other important elements were also released initiating plankton hy-perproductivity (Gaucher et al., 2003) and 13C levels were enriched (Halverson et al., 2005). The changing oceans caused the atmosphere to evolve to its oxygenated state (Canfield et al., 2007; Canfield and Teske, 1996; Garrels et al., 1973) and the most intense periods of glaciation in Earth’s history (Hoffman et al., 1998; Kirschvink, 1992; Roberts, 1971). These extreme glacial events are suggested to be partly responsible for the birth of diverse animal life (Bowring and Erwing, 1998; Knoll, 1992; Narbonne and Gehling, 2003) and us such understanding them is crucial to our knowledge of the Earth system.
The central aim of this thesis is to investigate some examples of Neoproterozoic sedimentary basins that record evidence for these glacial events and the tectonic history of their cratonic roots in their journey from Rodinia to Gondwana. This is achieved through detailed sedimentary, geochronological and palaeomagnetic studies with a focus on western Gondwana.
The specific aims of this thesis are:1. Shed light on the relationship between Rodinian rifting and glaciation from the Damara Belt in
Namibia and to show that there is a glacial influence on sedimentation.2. Constrain the termination of deformation in the Paraguay Belt
3. Delineate a glacial incision surface along the Serra Azul in the northern Paraguay Belt and dis-cuss other global evidence for similar aged glacial deposits.
4. Provide a detailed sedimentary and stratigraphic analysis of the Serra Azul Formation comple-mented by Argon cooling ages to provide the first age constraints on the Serra Azul Formation and informa-tion on low temperature events within the northern Paraguay Belt
5. Provide a long-awaited and comprehensive detrital zircon study from the northern Paraguay Belt and discuss the now significant body of evidence that exists for a Cambrian age of orogenesis.
6. To show that new palaeomagnetic data from the Alto Paraguay Group suggest a significant remagnetisation event occurred in the northern Paraguay Belt, most likely in the Jurassic.
The location for the first aim was selected in Namibia based on the excellent exposure of Neopro-terozoic rift basins in the Damara Belt. The Toekems Sub-basin contains a unique exposure of rift-related sediments under a Sturtian aged cap-carbonate.
The remaining aims are addressed in the northern Paraguay Belt in central South America, which provides a place where the relationship between tectonics, oceans, atmosphere and the biosphere during the Neoproterozoic–Cambrian can be studied. The belt is comprised of a thick succession of passive mar-gin sediments on the southwestern edge of the Amazonian Craton. Mounting evidence suggests that the Paraguay Belt marks the suture zone of the Clymene Ocean, which separated Amazonia, Rio Apa, Pampia and proto-Gondwana (Bandeira et al., 2011; Tohver et al., 2011; Tohver et al., 2010; Trindade et al., 2006).
REFERENCES CITED
Bandeira, J., McGee, B., Nogueira, A.C.R., Collins, A.S., Trindade, R.I.F., 2011. Closure of the Neoproterozoic Clymene Ocean: sedimentary and detrital zircon geochronology evidence from the siliciclastic upper Alto Paraguai Group, northern Paraguay Belt, Brazil. Gondwana Research.
Bowring, S., Erwing, D.H., 1998. A new look at evolutionary rates in deep time: uniting paleontology and high-precision geochronol-ogy. GSA Today 8, 1-8.
Campbell, I.H., Davies, G.F., 2006. Do mantle plumes exist? Episodes 29, 162-168.Canfield, D.E., Poulton, S.W., Narbonne, G.M., 2007. Late-Neoproterozoic deep-ocean oxygenation and the rise of animal life. Sci-
ence 315, 92-95.Canfield, D.E., Teske, A., 1996. Late Proterozoic rise in atmospheric oxygen concentration inferred from phylogenetic and sulphur-
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isotope studies. Nature 382, 127-132.Condie, K.C., 1998. Episodic continental growth and supercontinents: a mantle avalanche connection? Earth Planet. Sci. Lett. 163,
97-108.Frimmel, H.E., Zartman, R.E., Spath, A., 2001. The Richtersveld Igneous Complex, South Africa: U-Pb Zircon and Geochemical Evi-
dence for the Beginning of Neoproterozoic Continental Breakup. Journal of Geology 109, 493-508.Garrels, R.M., Perry, E.A., Mackenzi.Ft, 1973. Genesis of Precambrian iron-formations and development of atmospheric oxygen.
Economic Geology 68, 1173-1179.Gaucher, C., Boggiani, P.C., Sprechmann, P., Sial, A.C., Fairchild, T.R., 2003. Integrated correlation of the Vendian to Cambrian Ar-
royo del Soldado and Corumba´ Groups (Uruguay and Brazil): palaeogeographic, palaeoclimatic and palaeobiologic implications. Precambrian Research 120, 241-278.
Halverson, G.P., Hoffman, P.F., Schrag, D.P., Maloof, A.C., Rice, A.H.N., 2005. Toward a Neoproterozoic composite carbon-isotope record. GSA Bulletin 117, 1181-1207.
Hoffman, P.F., Kaufman, A.J., Halverson, G.P., Schrag, D.P., 1998. A Neoproterozoic snowball earth. Science 281, 1342-1346.Kaufman, A.J., Hayes, J.M., Knoll, A.H., Germs, G.J.B., 1991. Isotopic compositions of carbonates and organic carbon from up-
per Proterozoic successions in Namibia: stratigraphic variation and the effects of diagenesis and metamorphism. Precambrian Research 49, 301-327.
Kirschvink, J.L., 1992. Late Neoproterozoic low-latitude global glaciation: the Snowball Earth, in: Schopf, J.W., Klein, C. (Eds.), The Proterozoic Biosphere. Cambridge University Press, New York, pp. 51-52.
Knoll, A.H., 1992. Biological and biogeochemical preludes to the Ediacaran radiation, in: Lipps, J.H., Signor, P.W. (Eds.), Origin and Early Evolution of the Metazoa. Plenum Press, New York, pp. 53-84.
Li, Z.X., Bogdanova, S.V., Collins, A.S., Davidson, A., De Waele, B., Ernst, R.E., Fitzsimons, I.C.W., Fuck, R.A., Gladkochub, D.P., Jacobs, J., Karlstrom, K.E., Lu, S., Natapov, L.M., Pease, V., Pisarevsky, S.A., Thrane, K., Vernikovsky, V., 2008. Assembly, con-figuration, and break-up history of Rodinia: A synthesis. Precambrian Research 160, 179-210.
Li, Z.X., Li, X.H., Kinny, P.D., Wang, J., 1999. The breakup of Rodinia: did it start with a mantle plume beneath South China? Earth Planet. Sci. Lett. 173, 171-181.
Melezhiik, V.A., Gorokhov, I.M., Kuznetsov, A.B., Fallick, A.E., 2001. Chemostratigraphy of Neoproterozoic carbonates: implications for `blind dating’. Terra Nova 13, 1-11.
Mitrovica, J.X., Beaumont, C., Jarvis, G.T., 1989. Tilting of continental interiors by the dynamic effects of subduction. Tectonics 8, 1079-1094.
Narbonne, G.M., Gehling, J.G., 2003. Life after snowball: The oldest complex Ediacaran fossils. Geology 31, 27-30.Pysklywec, R.N., Mitrovica, J.X., 1997. Mantle avalanches and the dynamic topography of continents. Earth Planet. Sci. Lett. 148,
447-455.Roberts, J.D., 1971. Late Precambrian glaciation: an anti-greenhouse effect? Nature 234, 216-217.Tohver, E., Cawood, P.A., Rosello, E.A., Jourdan, F., 2011. Closure of the Clymene Ocean and formation of West Gondwana in the
Cambrian: evidence from the Sierras Australes of the southernmost Rio de la Plata craton, Argentina. Gondwana Research this volume.
Tohver, E., Trindade, R.I.F., Solum, J.G., Hall, C.M., Riccomini, C., Nogueira, A.C.R., 2010. Closing the Clymene ocean and bending a Brasiliano belt: Evidence for the Cambrian formation of Gondwana, southeast Amazon craton. Geology 38, 267-270.
Trindade, R.I.F., D’Agrella-Filho, M.S., Epof, I., Brito Neves, B.B., 2006. Paleomagnetism of Early Cambrian Itabaiana mafic dikes (NE Brazil) and the final assembly of Gondwana. Earth Planet. Sci. Lett. 244, 361-377.
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The research contained in this thesis has been published or submitted for publication in scientific journals. The bibliographic details of each journal article comprising a chapeter are listed at the beginning of the chapter, which includes the names of all authors involved in their production. The contribution of each author to the conceptualisation, realisation and documentation of these works is described below.
MCGEE, B. (Candidate)Chapters 1–6: Project conceptualisation and planning; fieldwork, including mapping and stratigraphic logging; sample selection and preparation; LA-ICPMS data collection; all calculations and data processing; data interpretation; manuscript design, writing and creation of all figures; article submission to journals.
I certify that the above statement is accurate
Signed Date
HALVERSON, G. P. (Supervisor)Chapter 1: Project conceptualisation and planning; fieldwork assistance; guidance with data interpretation; guidance with manuscript ouline; manuscript review.
I certify that the above statement is accurate and give permission for the relevant manuscripts to be included in this thesis
Signed Date 5/02/13
COLLINS, A. S. (Supervisor)Chapters 1–6: Project conceptualisation and planning; fieldwork assistance; guidance with data interpretation; guidance with manuscript ouline; manuscript review.
I certify that the above statement is accurate and give permission for the relevant manuscripts to be included in this thesis
Signed Date 24/01/13
TRINDADE, R. I. F. (Supervisor)Chapters 2–6: Project conceptualisation and planning; fieldwork assistance; guidance with data interpretation; guidance with manuscript ouline; manuscript review.
I certify that the above statement is accurate and give permission for the relevant manuscripts to be included in this thesis
Signed Date 30/01/13
Author Contribution Statement
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JOURDAN, F.Chapter 4: Argon isotope data collection; assistance with data preparation and interpretation; manuscript review.
I certify that the above statement is accurate and give permission for the relevant manuscripts to be included in this thesis
Signed Date 5/02/13
ROSAFFA, M.Chapter 6: sample preparation and data collection.
I certify that the above statement is accurate and give permission for the relevant manuscripts to be included in this thesis
Signed Date 20/02/13
TOHVER, E.Chapter 6: guidance with data interpretation; guidance with manuscript outline
I certify that the above statement is accurate and give permission for the relevant manuscripts to be included in this thesis
Signed Date 13/02/13
Chapter 1: Cryogenian rift-related magmatism and sedimentation: South-western Congo Craton, Namibia.
This chapter is published as:McGee, B., Halverson, G.P. and Collins, A.S., 2012. Cryogenian rift-related magmatism and sedimentation: South-western Congo Craton, Namibia. Journal of African Earth Sciences 76, 34-49.
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Chapter 1 Cryogenian rift-related magmatism and sedimentationChapter 1 Cryogenian rift-related magmatism and sedimentation
A McGee, B., Halverson, G.P. & Collins, A.S. (2012) Cryogenian rift-related magmatism and sedimentation: South-western Congo Craton, Namibia. Journal of African Earth Sciences, v. 76, pp. 34-49
NOTE:
This publication is included on pages 3-18 in the print copy of the thesis held in the University of Adelaide Library.
It is also available online to authorised users at:
http://dx.doi.org/10.1016/j.jafrearsci.2012.09.003
Chapter 2: G’day Gondwana - the final accretion of a supercontinent: U-Pb ages from the post-orogenic São Vicente Granite, northern Paraguay Belt, Brazil
This chapter is published as:McGee, B., Collins, A.S., Trindade, R.I.F., 2012. G’day Gondwana - the final accretion of a supercontinent: U-Pb ages from the post-orogenic Sao Vicente Granite, northern Paraguay Belt, Brazil. Gondwana Research 21, 316-322.
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Chapter 2 Cryogenian rift-related magmatism and sedimentation
A McGee, B., Collins, A.S. & Trindade, R.I.F. (2012) G'day Gondwana - the final accretion of a supercontinent: U-Pb ages from the post-orogenic Sao Vicente Granite, northern Paraguay Belt, Brazil. Gondwana Research, v. 21(2-3), pp. 316-322
NOTE:
This publication is included on pages 21-27 in the print copy of the thesis held in the University of Adelaide Library.
It is also available online to authorised users at:
http://dx.doi.org/10.1016/j.gr.2011.04.011
Chapter 3: A glacially incised canyon in Brazil: Further evidence for mid-Ediacaran glaciation?
This chapter is published as:McGee, B., Collins, A.S. and Trindade, R.I.F., Accepted. A glacially incised canyon in Brazil: Further evidence for mid-Ediacaran glaciation? The Journal of Geology.
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Chapter 3 A glacially incised canyon in Brazil
A McGee, B., Collins, A.S. & Trindade, R.I.F. (2013) A glacially incised canyon in Brazil: further evidence for mid-Ediacaran glaciation. The Journal of Geology, v. 121(3), pp. 275-287
NOTE:
This publication is included on pages 31-42 in the print copy of the thesis held in the University of Adelaide Library.
It is also available online to authorised users at:
http://dx.doi.org/10.1086/669979
Chapter 4: The tectonic and palaeoenvironmental significance of the Ediacaran to Cambrian Alto Paraguay Group, Paraguay Belt, Brazil: Sedimentology and 40Ar/39Ar detrital muscovite provenance
This chapter is under review as:McGee, B., Collins, A.S., Trindade, R.I.F. and Jourdan, F. Under review. The tectonic and palaeoenvironmental significance of the Ediacaran to Cambrian Alto Paraguay Group, Paraguay Belt, Brazil: Sedimentology and 40Ar/39Ar detrital muscovite provenance. Sedimentology.
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Chapter 4 The tectonic and palaeoenvironmental significance of the Alto Paraguay Group
The tectonic and palaeoenvironmental significance of the Edia-caran to Cambrian Alto Paraguay Group, Paraguay Belt, Brazil: Sedimentology and 40Ar/39Ar detrital muscovite provenance
MCGEE, B.a, COLLINS, A.S.a, TRINDADE, R.I.F.b and JOURDAN, F.c
aCentre for Tectonics, Resources and eXploration (TRaX), School of Earth and Environmental Sciences, B09, Mawson Building, The University of Adelaide, SA 5005, Australia.bDepartamento de Geofísica, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Rua do Matão, 1226, 05508-090, São Paulo, Brazil.cWestern Australian Argon Isotope Facility, Department of Applied Geology and John de Laeter Centre, Curtin University, GPO Box U1987, Perth, Western Australia, 6845, Australia
ABSTRACT
The Alto Paraguay Group in the northern Paraguay Belt, Brazil contains unequivocal evidence for a glacial influence on sedimentation. Within the Serra Azul Formation, multi-directional striations on sandstone clasts and striated, polished and bullet-shaped mudstone clasts have all been documented. However, a palaeodepositional model is not well established and due to a paucity of geochronological data its age is not well constrained. Given that the Serra Azul Formation is interpreted as being deposited during the Gaskiers glaciation, it is important to correctly understand its position within the Neoproterozoic tectono-stratigraphic framework. This contribution presents a detailed stratigraphy surrounding the Serra Azul Formation to show that it was deposited in a glacio-fluvial environment and on a lithostratigraphic basis the Serra Azul Formation is assigned to the basal part of the Alto Paraguay Group. A significant number of single grain 40Ar/39Ar detrital muscovite cooling ages (ca. 120) from the Alto Paraguay Group are also presented. The three youngest grains yield a weighted mean age providing a robust maximum depositional age of the Serra Azul Formation at 640 ± 15 Ma. This age, when considered with other data, suggest that the Serra Azul Formation developed in a mid-Ediacaran glaciation consistent with that expressed in the Gaskiers Formation of Newfoundland, Canada. 40Ar/39Ar ages from the upper part of the Alto Paraguay Group are as young as 544 ± 7 Ma, consistent with mounting evidence that indicate a Cambrian age for orogenesis within the Paraguay Belt at the final amalgamation of Gondwana.
INTRODUCTION
Identifying glacial deposits in the geological record is a longstanding and contentious issue. This is mostly due to the impact that the interpretations of these successions have on our understanding of Earth history. A recent contribution by Arnaud and Etienne (2011) concisely summarises key characteristics of Neoproterozoic glacial environments, pointing out that the presence of striations, faceting and bullet-shaped clasts confirms a glaciogenic influence on sedimentation. Global correlation of the fragmented Neoproterozoic glacial record is also another controversial issue. Existing evidence implies that there were at least three major glacial events during the Neoproterozoic; a middle Cryogenian event (~720 Ma ‘Sturtian’); an end-Cryogenian event (~635 Ma ‘Marinoan’) and a middle Ediacaran event (~582 Ma ‘Gaskiers’; Halverson et al., 2009). While reasonable evidence exists to suggest that the first two were global in extent (Hoffman et al., 1998), global correlation of younger Ediacaran glacial deposits has proven to be problematic. This may be due
to diachroneity, but available evidence is suggestive that the mid-Ediacaran event is at least visible in the global sedimentological record (McGee et al., Under review).
The timing of formation of the Palaeozoic supercontinent Gondwana is another issue that has received significant attention in the literature for many decades. Early interpretations of a collision between two large continents called East Gondwana and West Gondwana at ~650 Ma (Stern, 1994) have evolved to incorporate current evidence that identify a network of collisional events between relatively small Neoproterozoic continents that amalgamated to form Gondwana during the Ediacaran and Cambrian (e.g. Collins and Pisarevsky, 2005; Meert, 2003; Pisarevsky et al., 2008). The Paraguay Belt in Brazil is part of this network of Gondwana-forming orogens that for some time has been considered as ‘Brasiliano’ (ca. 940 – 630 Ma) in age (Cordani et al. 2009). More recent contributions (Bandeira et al., 2012; McGee et al., 2012; Tohver et al., 2011; Trindade et al., 2006) have demonstrated that the Paraguay Orogen is part of a larger
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Chapter 4 The tectonic and palaeoenvironmental significance of the Alto Paraguay Group
orogenic belt that can be traced south to Argentina and north to the Amazon, and that is considerably younger than many Gondwana-amalgamation orogens—forming in the early Cambrian—therefore representing one of the final collisional belts in Gondwana.
This work addresses both the tectonic and palaeoenvironmental issues outlined above through presentation of detailed stratigraphic sections from the northern Paraguay Belt within the Alto Paraguay Group. The sedimentological work shows that the Serra Azul Formation was deposited in a glacio-fluvial environment. The new 40Ar/39Ar detrital muscovite ages show that the Serra Azul Formation clearly represents a glacial episode younger than ~640 Ma. The argon isotopic data also corroborates other radiometric ages that indicate orogenesis within the Paraguay belt is early Cambrian in age.
REGIONAL SETTING
The Paraguay Belt is located in central South America (Figure 1) and marks the boundary between the Amazon, São Francisco, Rio Apa and Rio de la Plata cratons. It comprises metamorphosed Neoproterozoic sedimentary strata that were deposited in a passive margin environment (Nogueira et al., 2007). These metasedimentary and sedimentary rocks are divided into the older pelites, diamictites and siliciclastics of the Cuiabá Group in the core of the orogen (Barros et al., 1982), diamictites of the Puga Formation, carbonates of the Araras Group and siliciclastics of
the upper Alto Paraguay Group. Whilst the nature of the contact between the Cuiabá Group and Puga Formation not well understood due to non-exposure, recent interpretations describe the Puga diamictite as the proximal ‘shelf’ facies of the extensive Cuiabá Group (Figure 1; Alvarenga et al., 2009). The age of the youngest detrital zircon in the Puga Formation is 706 ± 9 Ma (Babinski et al., 2012), which when coupled with the δ13C (5.0‰) and 87Sr/86Sr (0.7080) ratios from carbonates directly overlying the diamictites (Nogueira et al., 2003), suggest that these diamictites represent the ~635 Ma end-Cryogenian glaciation.
In the northern Paraguay Belt the stratigraphic framework of the Alto Paraguay Group—the focus of this study—was first described by Almeida (1964) who divided it into the ~1600 m sands, silts and shales of the Raizama Formation, overlain by ~900 m of shales, silts and sandstones of the Sepotuba Formation and ~600 m of Diamantino Formation siliciclastic rhythmites and sandstones. More recently Alvarenga et al. (2007) described a new unit, the Serra Azul Formation, in between carbonates of the Araras Group and the siliciclastics of the Alto Paraguay Group. The basal part of this formation is composed of a glaciogenic diamictite containing multiply striated sandstone clasts (Alvarenga et al., 2007) and striated, polished and bullet-shaped mudstone clasts (McGee et al., Under review), which is overlain by a transgressive package of interlayered silts and fine sands. The siltstone and sandstone of the upper Alto Paraguay Group are interpreted to be shed off rising topography—the evolving Paraguay orogen—
Fig. 1. Geological map showing lithostratigraphic relationships within the northern Paraguay Belt. Modified from CPRM Cuiabá 1:1000000 map sheet (Barros et al., 1982).
A NOTE:
This figure/table/image has been removed to comply with copyright regulations. It is included in the print copy of the thesis held by the University of Adelaide Library.
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Chapter 4 The tectonic and palaeoenvironmental significance of the Alto Paraguay Group
in response to collision between the Amazon, the São Francisco and the Paraná cratons between ~540–520 Ma (Bandeira et al., 2012). The termination of orogenesis was marked by intrusion of post-orogenic granites into the base of these Neoproterozoic sediments at 518 ± 4 Ma (McGee et al., 2012).
ANALYTICAL METHODS
Detrital muscovite 40Ar-39Ar isotopic analysisFour fresh samples within the Alto Paraguay Group were selected from the northern Paraguay Belt for 40Ar/39Ar muscovite dating. Unaltered, optically transparent, 100–150 µm muscovite grains were separated and carefully handpicked under a binocular microscope and subsequently cleaned in a sonic bath of deionized water. Samples were loaded into aluminum discs with wells of 1.9 cm diameter and 0.3 cm depth, which were themselves bracketed by pits that included Fish Canyon sanidine (FCs) used as a neutron fluence monitor for which an age of 28.305 ± 0.036 Ma (1σ) was adopted (Renne et al., 2010) based on the calibration by (Jourdan and Renne, 2007). The disc was Cd-shielded to minimize undesirable nuclear interference reactions and irradiated in position 5C for 25 hours in the Hamilton McMaster University nuclear reactor in Canada. The mean J-value computed from standard grains within the small pits was 0.00954500 ± 0.00001145 determined as the average and standard deviation of J-values of the small wells for each irradiation disc. Mass discrimination was monitored using an automated air pipette and provided a mean value of 1.00543 ± 0.00004 per dalton (atomic mass unit) relative to an air ratio of 298.56 ± 0.31 (Lee et al., 2006). The correction factors for interfering isotopes were (39Ar/37Ar)Ca = 7.30x10-4 (± 11%), (36Ar/37Ar)Ca = 2.82x10-4 (± 1%) and (40Ar/39Ar)K = 6.76x10-4 (± 32%).
Ar isotopic analyses were performed at the Western Australian Argon Isotope Facility at Curtin University. Each muscovite grain was fused in one, two or in some rare cases three steps using a 110 W Spectron Laser Systems, with a continuous Nd-YAG (IR; 1064 nm) laser. The gas was purified in a stainless steel extraction line using one SAES AP10 getter and one SAES GP50 getter for the largest grains. Ar isotopes were measured in static mode using a MAP 215-50 mass spectrometer (resolution of ~400; sensitivity of 4x10-14 mol/V) with a Balzers SEV 217 electron multiplier mostly using 9 to 10 cycles of peak-hopping. The data acquisition was performed with the Argus program written by M.O. McWilliams and ran under a LabView environment. The raw data were processed using the ArArCALC software (Koppers, 2002) and the ages have been calculated using the decay constants recommended by Renne et al. (2010). Blanks were monitored every 3 to 4 steps and typical 40Ar blanks range from 1 x 10-16 to 2 x 10-16 mole. Ar isotopic data corrected for blank, mass discrimination and radioactive decay are given in Supplementary Table 1. Ages represent either the total fusion age or are calculated using the mean of
concordant heating steps, each weighted by the inverse variance of their individual analytical error.
MEASURED SECTIONS
In their first presentation of the Serra Azul Formation, Alvarenga et al. (2007) provided a cross section from the southern slopes of Serra Azul (Figures 1 and 2) dividing the formation up into two informal units; Unit A, a massive diamictite and Unit B, a mudstone-siltstone unit. In a subsequent contribution, Figueiredo et al. (2011) stated that the Serra Azul Formation is between 250 and 300 m thick in the region where it is completely exposed, however, the base of the Serra Azul Formation was not documented. McGee et al. (Under review), recently demonstrated the extreme thickness variations of the Serra Azul Formation, and interpreted that these were due to infilling of an incised topography.
4.1 Serra Azul sectionThe type locality for the Serra Azul Formation is located at the eponymous farm, on the southern limb of the large (15 km wide), tight, shallowly east-plunging Serra Azul syncline (Figure 1). The surface distance between outcrops of Araras Group carbonate and Serra Azul Formation diamictite is approximately 300 m (Figures 2a & b). This equates to ~170 m of unaccounted stratigraphy (using the average bedding inclination in the region). At this location the diamictite layer has a reddish/purple fine silty matrix (Figure 3a). Clast sizes are highly variable from a few millimetres to 10 cm and also vary in degrees of roundness from angular to well-rounded and they are predominantly composed of quartz, purple laminated siltstone, mudstone, chert, sandstone, feldspathic and micaceous granite, gneiss and blue/grey carbonate (Figure 3a). A significant number of the mudstone clasts are highly polished and striated and are bullet shaped (McGee et al., Under review).
The top of the diamictite represents a flooding surface, signified by the presence of fine, deep water siltstones (Figure 2c). The overlying package is a series of post-glacial progradational parasequences that coarsen-up on the scale of 10’s of metres. They begin with fine silts that show increasing levels of sandy input, both within the silt layers themselves and as discrete sandstone interlayers. The silts alternate between yellow and a deep purple colour and are often finely laminated on a millimetre scale. These parasequences are interpreted to represent prograding shelf sediment on the margin of the Amazon Craton.
There is a general shallowing-upward trend in the section from finely laminated deep water silts to the overlying storm and tidal dominated sandstones of the Raizama Formation as accommodation space was reduced. This is recognised by the gradual appearance of shallower-water facies including starved ripples, trough and planar cross-stratification, sinuous ripple crest casts (Figure 3b), tidal bundles and an increase in
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Chapter 4 The tectonic and palaeoenvironmental significance of the Alto Paraguay Group
coarser material upward in the sequence concomitant with a progressive loss of the deeper water facies (finely laminated silts). Alvarenga et al. (2007) described the contact between the Serra Azul Formation and the Raizama Formation as ‘sharp’. However, the observations presented here indicate that there is a progressive increase in sand content in the Serra Azul Formation suggesting a gradational boundary is a more suitable description. It is therefore proposed that a logical placement for the base of the Raizama Formation is when the lower/upper shoreface facies begin to dominate over the more distal offshore facies or with the beginning of thick (>1 m) sandstone layers.
Heading north, stratigraphically above the measured section, outcrop is sporadic but the transition from the Raizama Formation to the Sepotuba Formation is inferred based on a colour change to lighter coloured outcrop, visible in the satellite image (Figure 2b). The estimated thickness of the Raizama Formation based on this division is 960 m, using the average bedding inclination in the area. Outcrops dispersed within the Sepotuba Formation here are predominantly yellow and pale grey/blue siltstones with interlayered fine and medium sandstone and minor coarse sands and pebble conglomerates (Figure 2a). The transition from the Sepotuba Formation to red and purple finely laminated silts and interlayered fine sands of the Diamantino Formation was observed in outcrop and is expressed in the satellite image with the appearance of finer, more planar form lines (Figure 2b & c). The estimated thickness of the Sepotuba Formation is 820 m, which compares well to the 900 m estimate of Almeida (1964).
4.2. Boa Sorte sectionThe Boa Sorte section, named after the eponymous farm it passes through, is located 66 km east of the type section along the same southern limb of the Serra Azul syncline (Figure 1). Such a detailed section was made possible by the recent construction of a new road through the range at this location. Geological mapping in the area shows that the Puga Formation diamictite is present south of the measured section (Figure 4a). At this location the Puga diamictite is massive and contains predominantly centimeter-scale clasts of granite and quartzite within a sandy matrix (Figure 3c). Lying above the Puga Formation are a sequence of vuggy and brecciated pink carbonate and chert (Figure 3d) that is interpreted to belong to the Serra do Quilombo Formation of the Araras Group. Using the inclination of beds overlying these carbonates and the surface distance to the first appearance of the Serra Azul Formation, an estimated stratigraphic thickness of 1730 m is obtained for these carbonates. The contact between the carbonates and the Serra Azul Formation was not observed at this locality.
The Serra Azul diamictite is estimated to be significantly thicker at this section (~480 m; Figure 4c), which has been interpreted to signify the presence of an incised valley (McGee et al., Under review). The Serra Azul diamictite consists of a dull green/grey diamictite
with a silty to sandy matrix. The clast population is similar to the diamictite at the Serra Azul section with foliated granite, gneiss, rounded quartzite, sub-rounded clasts of grey chert and clasts of the underlying pink dolostone. This observation suggests an erosive base for Serra Azul Formation that has completely removed the Nobres Formation at this locality and cut down into the dolomitic Serra do Quilombo Formation. The interlayered silts and sands documented at the type section were identified above the diamictite and have an estimated thickness of 210 m.
The measured section begins with the first appearance of massive sandstone beds, responsible for the Serra Azul topography (Figure 4c). This is interpreted as the base of the Raizama Formation, a conclusion that matches the calculated stratigraphic thicknesses of the Raizama and Sepotuba formations. At this locality the basal Raizama Formation is dominated by a greater amount of silt than at the Serra Azul section. This may be indicative of a more distal position on the margin relative to the Amazon Craton resulting in finer grained sediment deposition. The section does, however, exhibit the same shallowing-upward trend, with the appearance of swaley cross stratification in the mud and silt layers and subsequent introduction of increasing amounts of planar-stratified sandstone and coarser pebble conglomerate layers or lenses. The Raizama Formation becomes very coarse at its top, with the uppermost part expressing a ~40m massively bedded sandstone unit. A platform to fluvio-deltaic depositional setting is proposed.
The transition to the Sepotuba Formation is signified by a major decrease in sand content and a return to the predominance of siltstone. This most likely occurred as a result of basin subsidence and increased accommodation space. Here the Sepotuba Formation is expressed as flaser bedded and wavy, pinch-and-swell, planar-stratified fine sandstones interlayered with millimeter-laminated siltstones (Figure 3e). This heterogeneous bedding is suggestive of high-energy deposition on a storm and tidally influenced setting where individual sand layers were subsequently covered by silty or muddy material. The interpretation of a high-energy environment is also consistent with the presence of rip-up clasts of mudstone within the basal parts of some sandstone layers (Figure 3f). These rip-up clasts imply that the tidal currents were strong enough to have peeled off the underlying mudstone layers (e.g. Le Roux et al., 2004) and incorporated them into the more siliciclastic layers. This package crops out for around 120 m before the outcrop becomes discontinuous. The remaining Sepotuba Formation thickness was calculated to be ~810 m, indicating an overall thickness of ~930 m in this section. The Diamantino Formation is not exposed at this location but is most likely represented by the break in slope from the range to the plain (Figure 4a and b).
4.3. Nobres sectionTwo sections were measured in the area near the town
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Chapter 4 The tectonic and palaeoenvironmental significance of the Alto Paraguay Group
Fig. 2. (a) Geological map at type locality of the Serra Azul Formation at the Serra Azul farm (b) Satellite image outlining major geological boundaries in white and location of measured sections (c) Serra Azul measured section.
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Chapter 4 The tectonic and palaeoenvironmental significance of the Alto Paraguay Group
Fig. 3. (a) Purple silty matrix of the Serra Azul diamictite supporting sub-angular clasts of carbonate and gneiss (b) Sinuous ripple crests in the Raizama Formation (c) Puga Formation diamictite showing clasts of quartzite and weathered granite (d) Vuggy and brecciated dolomite of the Serra do Quilombo Formation (e) Flaser, pinch and swell bedding in the Sepotuba Formation showing planar stratification in the sand-stone lenses (below coin) indicating flow the right (west) (f) Mudstone rip up clasts (circled) in sandstone layers in the Sepotuba Formation (g) Swaley cross-stratification in the Nobres Formation (h) Asymmetric ripple casts in the Nobres Formation (i) Asymmetric gravel ripples composed surrounded by coarse sand (j) Desiccation crack casts in the Serra Azul Formation. Coin is 27 mm in diameter.
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Chapter 4 The tectonic and palaeoenvironmental significance of the Alto Paraguay Group
of Nobres (Figure 5a & b), located in the NE-SW trending section of the northern Paraguay Belt (Figure 1). The area comprises a series of tight folds, plunging southwest and two similarly trending thrust faults (Figure 5a). Section A was measured on the southern limb of one of these folds at the Copacel quarry to document the uppermost part of the Nobres Formation and the transition to the basal part of the Serra Azul Formation. Section B, in conjunction with geological mapping, also captures this transition, on the northern limb of the same fold.
In section A of the Nobres Formation, it is possible to recognise the surfaces and sequences defined by Nogueira et al. (2007), with the lower section dominated by dark grey, laminated and silicified carbonate, contrasting with the significant siliciclastic input found in the upper section . The input of siliciclastic material occurs around 70 m into the section, where initial bed forms are wavy. Planar and swaley (Figure 3g) stratification are observed and evidence for unidirectional flow is inferred from the presence of asymmetric casts (Figure 3h) and asymmetric ripples (Figure 3i). These sedimentary structures are indicative of a shallow marine or lower shoreface/intertidal environment (e.g. Dalrymple, 1992; Walker and Plint, 1992). The parasequences are stacked progradational packages that commonly have a sandy base and fine upwards with interlayered silicified carbonates and mudstones on the scale of 10s of metres. Breccias were also observed but their pattern of cross-cutting bedding suggests they are not a primary depositional feature.
Siliciclastic material increases up-section until eventually at ~168 m a very coarse siliciclastic unit is reached. Nogueira et al. (2007) interpreted these siliciclastic deposits as belonging to the Raizama Formation. However, in light of the recent discovery of the Serra Azul Formation, this interpretation requires some discussion.
The Serra Azul diamictite is well documented along the Serra Azul above the Araras Group carbonates, despite the direct contact not being exposed there. Further west in the belt the Serra Azul diamictite has not been observed. Figueiredo et al. (2011) suggested that the diamictite is not observed in the west due to non-deposition or erosion after deposition. Erosion is not considered to be a likely possibility given that a flooding surface directly overlies the diamictite—such a transgressive systems tract is unlikely to result in erosion of the underlying sediments. Non-deposition is a possibility, if glaciation was a local feature, glacial rain-out would only be observed in the vicinity of glaciers.
A more accurate description than non-deposition is that the absence of the diamictite member is due to lateral facies changes within the Serra Azul Formation. Section B (Figure 5c), in conjunction with geological mapping (Figure 5d) also documents a transition from carbonate to overlying coarse-grained siliciclastics. This is interpreted to be correlative to the Serra Azul diamictite documented further east along the Serra
Azul.The parasequences in section B commonly fine
upwards on the scale of 5 m starting from a gravelly, or coarse sandy, base and fining upwards to fine or medium sands (Figure 5c). There are abundant grading sequences within these successions that also fine upwards. There are numerous lenses of pebbled material and swaley and planar stratification. Dessication cracks on the tops of some of the finer grained layers provide evidence for periods of sub aerial exposure (Figure 3j). These observations are indicative of a fluvially influenced tidal platform that was most likely exposed in response to glacioeustatic sea level fall associated with the Gaskiers glacial event (McGee et al., Under review).
40AR/39AR ISOTOPIC RESULTS
This study reports single grain ages for 121 muscovite grains (Figure 6 and Table 1). The broad age range of the muscovite populations within the samples indicates that large scale resetting has not occurred and that in-situ temperatures reached during orogenesis were below the closure temperature of Ar in muscovite, ~450 ± 50 °C (Harrison et al., 2009), which is supported by the un-metamorphosed nature of the rocks. The 32 muscovites analysed from the Serra Azul Formation yielded Palaeoproterozoic to Neoproterozoic ages (~2050 to ~613 Ma). The results are spread out over a near linear array in the Meso- and Neoproterozoic with a separate cluster in the Palaeoproterozoic. The 3 youngest ages define a small cluster with a weighted mean age of 640 ± 15 Ma (MSWD = 0.75; P= 0.47).
Thirty muscovites were analysed from the Raizama Formation giving Mesoproterozoic to Neoproterozoic ages (1520 to 899 Ma). One prominent age cluster is apparent in the Tonian with 11 grains defining a concordant set of ages, from which a weighted mean age of 924 ± 7 Ma (MSWD = 1.3, P = 0.24) was calculated. The youngest age (899 Ma) is not concordant with this group and it is not clear if it is affected by 40Ar loss or if it provides the true minimum of the age population. The remaining grains define a broad spread of older ages.
Two samples of the Diamantino Formation were analysed, the stratigraphically lower of the two (BDM-09), yields ages ranging from the Ediacaran to the early Mesoproterozoic (583 to 1074 Ma). The predominant age population in this sample contained 23 concordant earliest Ediacaran ages that yielded a weighted mean of 631 ± 9 Ma (MSWD = 1.10; P = 0.34), and a smaller population of four muscovites that yielded Mesoproterozoic concordant ages with a weighted mean of 1054 ± 24 Ma (MSWD = 0.55; P = 0.65). The second Diamantino Formation sample (BDM-12), the stratigraphically highest sample from the Alto Paraguay Group, gave Palaeoproterozoic to Cambrian (1749 to 524 Ma) ages. The youngest ages define a concordant population of 12 Cambrian ages, from which a weighted mean of 544 ± 7 Ma (MSWD = 0.71, P=0.73) was calculated. In addition, the largest proportion of the data
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Chapter 4 The tectonic and palaeoenvironmental significance of the Alto Paraguay Group
Fig. 4. (a) Geological map at the Boa Sorte farm (b) Satellite image outlining major geological boundaries in white and location of measured sections (c) Boa Sorte measured section.
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Chapter 4 The tectonic and palaeoenvironmental significance of the Alto Paraguay Group
Fig. 5. (a) Geological map surrounding the town of Nobres showing SW plunging folds (b) Satellite image outlining major geological boundar-ies in white and location of measured sections (c) Composite stratigraphic section compiled from the Nobres region.
lie in the Cyrogenian to Cambrian with only four grains older than this group.
DISCUSSION
6.1. Facies variations and relative sea level change exhibited by the Alto Paraguay GroupThe large variation in thickness of the Serra Azul diamictite, the presence of carbonate clasts and the complete removal of Araras Group carbonates in some locations indicate significant erosion at the base of this formation. As previously discussed, the Serra Azul Formation exhibits lateral facies variations across the northern Paraguay Belt from a glaciomarine environment
in the east to a fluvially influenced tidal platform in the west. This interpretation accounts for why the Serra Azul diamictite is absent in the sections measured in the north-western part of the belt. A significant marine transgression after diamictite deposition is signified by the overlying fine-grained, deep-water siltstones. A progressive facies change follows with a shallowing-upward trend including the increasing sand content and shallower water sedimentary features of the Raizama Formation. This deep-to-shallow facies trend is repeated above the Raizama Formation with the appearance of fine grained mudstone and siltstone of the Sepotuba Formation. The final shallowing and deposition is encapsulated in the Diamantino Formation from the
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Chapter 4 The tectonic and palaeoenvironmental significance of the Alto Paraguay Group
basal turbidites, to a lake/prodelta setting followed by progradation of a delta front into the Diamantino Lake (Bandeira et al., 2012)
6.2. Maximum depositional ages of the Alto Paraguay GroupPrecise detrital zircon U-Pb age data in sedimentary rocks are widely used to provide first order constrains on palaeotectonic and palaeogeographic reconstructions owing to their capacity to fingerprint the provenance of sediments (Collins et al., 2012; Plavsa et al., Submitted). Detrital zircons are, however, limited in the information they record. The high closure temperature of Pb in zircon and the lack of new widespread zircon growth below upper amphibolite-facies conditions mean that low-temperature processes are largely invisible to zircon studies. The robust nature of the mineral also means that recycling of individual zircon crystals is a real consideration; the analysed detrital zircon may have passed through a number of previous sedimentary rocks before being deposited in the sample of interest. The application of 40Ar/39Ar single muscovite grain cooling or crystallisation ages to provenance analysis largely overcomes these problems as firstly, muscovite is considerably less robust than zircon. Muscovites are unlikely to survive more than one sedimentary cycle or even a very long waterborne transport (e.g. pancontinental river systems) and therefore the information encoded in detrital muscovite ages can be generally considered to offer constraints on proximal source areas where “primary” muscovite bearing rocks (namely peraluminous granites and medium to high-grade metamorphic rocks of pelitic-psammitic composition) were present. This means that muscovite ages preferentially provide information on the nearest source areas, therefore complementing and building on U-Pb zircon age data (e.g. Gutierrez-Alonso et al., 2005; Murphy and Collins, 2008). Secondly, since the closure temperature for Ar in muscovite is quite low (350–450˚C), detrital muscovite ages contain information on greenschist-facies events and the exhumation history of the source region – information that isn’t revealed by U-Pb zircon studies. Such muscovite ages are likely to be closer in age to the deposition of the sediment in question than U-Pb zircon ages, and therefore are likely to provide a tighter constrain the age of deposition. A caveat to the use of detrital 40Ar-39Ar muscovite ages is that the low closure temperature means that this technique is restricted to rocks that have not been metamorphosed above anchizone conditions after their deposition (i.e. post-depositional temperatures <350˚C).
The 40Ar/39Ar analyses of white mica reported here complement recent detrital zircon studies (McGee et al., Submitted) by providing constraints on source regions and recognising the age of lower temperature (<450 °C) events in the northern Paraguay Belt. The maximum depositional ages here are based on the ages of the youngest concordant cluster of detrital muscovite grains for each respective formation. Using
Fig. 6. Age distribution plots for 40Ar/39Ar cooling ages from single grain muscovites from the Alto Paraguay Group. Black vertical bars indicate the grains used in maximum depositional age calculations.
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Chapter 4 The tectonic and palaeoenvironmental significance of the Alto Paraguay Group
a cluster of ages instead of the (single) youngest age provides the following advantages: (1) since this study deals with total fusion ages where it is impossible to test if the muscovite has been partially reset (which would result in a fickian diffusion profile if the grain were to be step-heated), this approach makes the minimum age calculation relatively insensitive to eventual 40Ar loss by the youngest grain(s); (2) as many grains are very small and thus analytically challenging to analyze, this approach prevents using analytical outliers as a geological minimum, (3) it provides an analytically more precise maximum depositional age compared to a single grain that could be plagued with uncertainties as large as 50 Ma due to the small size of the grains analyzed and (4) the reproducibility of ages observed for the youngest groups of grains gives support to the grains being derived from a single young and nearby source. A drawback is that the youngest possible limit might be missed, but this is largely compensated by a gain in accuracy and thus gives better confidence in the data and interpretation. Using this reasoning the Serra Azul Formation is interpreted to be deposited no earlier than 640 ± 15 Ma. The overlying Raizama Formation has a maximum depositional age of 924 ± 7 Ma. The uppermost unit of the Alto Paraguay Group, the Diamantino Formation, has the youngest maximum depositional age of the analyses presented here at 544 ± 7 Ma.
6.3. Sources of the Alto Paraguay GroupThe 40Ar/39Ar muscovite ages from the sedimentary units analysed here are displayed in Figure 6, spanning the early Cambrian to the Palaeoproterozoic. Neighbouring geological terranes with these same age populations are considered here as possible source regions.
Since the Paraguay Belt is considered to be a sequence of folded sedimentary rocks that formed on a passive margin on the Amazon Craton (Alvarenga and Trompette, 1992), this is the most obvious location to consider potential sources. This craton comprises two small Archaean cores—the Central Amazonian Province (>2600 Ma)—surrounded by predominantly accretionary Palaeoproterozoic belts; the Maroni-Itacaiunas Province (2250–2050 Ma); the Ventuari-Tapajós Province (1980–1810 Ma); the Rio Negro-Juruena Province (1780–1550 Ma); the Rondonian-San Ignácio Province (1550–1300 Ma) and the ca. 1250–950 Ma Sunsás Province (Cordani and Teixeira, 2007; Cordani et al., 2009; Tassinari et al., 2000). These source regions can account for all of the pre-Neoproterozoic and Tonian ages reported here. However, the formations analysed here in the Alto Paraguay Group also contains inheritance of Cryogenian-aged material— such ages are not reported from the Amazon Craton.
To the east of the Paraguay Belt a number of Neoproterozoic ages have been reported in the Goiás Massif and the Brasília Belt and could represent potential sources for the Alto Paraguay Group sedimentary rocks. From the Brasília Belt these ages include the foreland sequences of the Bambuí Group, the Vazante
Group and their correlatives (790 – 600 Ma) and the Macaúbas Group (950 – 650 Ma; Coelho et al., 2008 and references therein). A Cryogenian Pb/Pb age (740 ± 22 Ma) for sedimentary cover on the São Francisco Craton was reported by Babinski and Kaufman (2003). Ages from the Goiás Massif include a Rb/Sr age of 643 ± 19 Ma from granites and greenstones (Nilson et al., 1997; Pimentel and Fuck, 1994) and Sm/Nd age of 612 ± 66 Ma from mafic to ultramafic rocks (Nilson et al., 1997). A Nd provenance study in the northern Paraguay Belt by Dantas et al. (2009), did not include the Serra Azul Formation in the stratigraphic framework, but did come to the conclusion that material from the upper Alto Paraguay Group was sourced from the Goiás Massif or Brasília Belt to the east. A recent study by Bandeira et al. (2012) also drew the same conclusion based on analysis of palaeocurrent indicators in the upper Alto Paraguay Group. These regions are therefore considered to be the best candidates for sources of the mid- to late-Neoproterozoic ages in the Alto Paraguay Group sediments.
A significant number of the 40Ar/39Ar muscovite analyses are, however, much younger than the reported ages in the Goías Massif and the Brasília Belt. Late Cryogenian–Ediacaran intrusive plutons are found in the present-day core of the Paraguay Belt (Ferreira, 2009; McGee et al., 2012). Erosion of these plutons concomitant with the rising topography of the Paraguay Orogen was suggested as a source for the younger Ediacaran ages by Bandeira et al. (2012). Another possible source for these younger muscovite grains is that they represent grains formed during metamorphism within the belt. The lack of a strong metamorphic overprint or the presence of metamorphic minerals suggests that the presently exposed section of the Paraguay Belt did not reach high temperatures. However, if temperatures did rise above ca. 350˚C in the orogenic hinterland, it is conceivable that some of these grains record exhumation and cooling through the muscovite cooling temperature. If this is the case, a circa 544 ± 7 Ma age for exhumation corroborates well with the end of orogenesis at 518 Ma proposed by (McGee et al., 2012).
6.4. Sedimentary-tectonic model for the formation of the Alto Paraguay GroupThe interpretation of source regions for the Paraguay Belt has important implications for its evolution and tectonic models of Gondwana formation. The Paraguay Belt has for some time has been considered as ‘Brasiliano’ (ca. 940 – 630 Ma) in age (Cordani et al. 2009). However, mounting evidence indicates that it is considerably younger than other orogens involved in suturing Gondwana. To date, no post-Tonian ages have been reported from the Amazon Craton, leading to hypotheses that invoke an easterly source for the late Cryogenian to Ediacaran aged sediments reported here. If this hypothesis is correct and the younger material did come from the east, tectonic inversion of the passive margin, responsible for deposition of the
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Chapter 4 The tectonic and palaeoenvironmental significance of the Alto Paraguay Group
Fig. 7. Tectonic model for the evolution of the Paraguay Belt. (a) Serra Azul glaciation at ca. 582 Ma. (b) Initiation of compression resulting in flexural warping of the lithosphere and deposition of the Raizama Formation into the proto-foredeep basin; (c) Continued lithospheric flexure and deepening of the foredeep basin; (d) Termination of orogenesis and deposition of the Diamantino Formation into the Diamantino Lake.
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Chapter 4 The tectonic and palaeoenvironmental significance of the Alto Paraguay Group
Puga Formation, Cuiabá Group and Araras Group, to a compressional collisional event is implied by the data presented here. A tectonic model is presented in Figure 7 that fits the currently available geological and radioisotopic data set.
Figure 7a shows the deposition of the Serra Azul Formation diamictite in a passive margin setting on the edge of the Amazon Craton. This formation, at the base of the Alto Paraguay Group, contains inheritance of Cryogenian-aged material. Basin inversion by the time the Serra Azul Formation was deposited is possible, however, the absence of Cryogenian and Ediacaran ages in the overlying Raizama Formation suggests that it occurred at some later stage. If this is the case, given that a glacial influence is recognised for the Serra Azul Formation (Alvarenga et al., 2007; McGee et al., Under review), the Cryogenian detritus in the Serra Azul Formation samples may have been transported from the present-day east by floating ice.
Deposition of the Raizama Formation is interpreted to be tectonically controlled by the initiation of topography, the ‘proto-Paraguay Orogeny’, in the form of a peripheral bulge (Figure 7b). Foreland basin systems form by flexural warping of the lithosphere that generate a downwarp proximal to the orogen, the foreland basin, and a low amplitude, long-wavelength upwarp, the peripheral bulge (Catuneanu et al., 1997). As indicated in Figure 7b, we suggest that the proto-Paraguay Belt was created by such a peripheral bulge—signifying the incipient stages of basin inversion had begun as oceanic crust connected to the Amazon Craton began to be underthrust beneath the Paranapanema Block and the Goiás Massif. A minor influence from volcanic arcs is interpreted in the Raizama Formation based on U-Pb ages reported by (McGee et al., Submitted). These arcs are now buried under the Paraná Basin, to the south east of the Paraguay Belt (Figure 1), and their presence and morphology has been interpreted based on petroleum wells and geophysical techniques (Mantovani and Brito Neves, 2009). Based on currently available ages the Raizama Formation was deposited after middle Ediacaran times (~582 Ma). The Raizama Formation also does not contain the prominent ~544 Ma detritus seen in the overlying Diamantino Formation suggesting that it probably predates this time.
After deposition of the Raizama Formation, a major decrease in sand content and the predominance of siltstone indicates deepening of the foreland basin (Figure 7c). This most likely occurred in response to increased lithospheric flexure as the collision advanced on the Amazonian margin. At this time the interlayered sandstones and siltstones of the Sepotuba Formation were deposited into the foreland basin. The heterogeneous nature of the material deposited in this formation and the presence of rip-up clasts indicates that this was a high-energy environment, influenced by strong currents and storms.
The stacking of progradational parasequences indicates that the basin was progressively filled with coarser sediment of the Diamantino Formation
(Figure 7d). Bandeira et al. (2012) interpreted the Diamantino Formation to record the final exhumation and erosion of the orogen that was deposited into the foreland basin—which they interpreted to be a closed system by this stage—the ‘Diamantino Lake’. Another indicator that the Diamantino Formation is likely to be lacustrine is that the majority of correlative marine Cambrian sequences contain fossils (e.g. Aceñolaza et al., 2009), whilst none have been reported for the Diamantino Formation. The predominance of much younger muscovite ages in the Diamantino Formation most likely represents the increased input from the upper plate of the colliding blocks (the Paranapanema block and Goiás Massif; Figure 7d) and, as previously discussed, the cannibalisation of igneous plutons from within the belt and metamorphic ages as the rocks were exhumed and cooled through the muscovite closure temperature. These ages for final sedimentation and exhumation at circa 544 Ma are in agreement with the observed intrusion of post-orogenic granites at 518 Ma (McGee et al., 2012) and indicate that detachment of the down-going oceanic slab and subsequent removal of the slab-pull force, resulting in the cessation of compressional tectonics, occurred around this time (Figure d).
CONCLUSIONSThe sedimentological work presented here indicates that the Serra Azul Formation was deposited in a glacio-fluvial environment. The three youngest muscovite grains analysed yield a weighted mean age providing a robust maximum depositional age for the Serra Azul Formation at 640 ± 15 Ma. This age, when considered with other data, suggest that the Serra Azul Formation developed in a mid-Ediacaran glaciation consistent with that expressed in the Gaskiers Formation of Newfoundland, Canada. 40Ar/39Ar ages from the upper part of the Alto Paraguay Group are as young as 544 ± 7 Ma, consistent with mounting evidence that indicate a Cambrian age for orogenesis within the Paraguay Belt at the final amalgamation of Gondwana. The tectonic model presented here, based on our sedimentary and stratigraphic analysis and these new ages, shows the transition from a marine passive margin environment to a compressional setting where the Paraguay Orogen formed as a peripheral bulge in the lithosphere of the Amazonian Craton.
ACKNOWLEDGEMENTSThe authors would like to thank Marly Babinski for her assistance in São Paulo, for access to laboratories and facilities required to write this manuscript. Ben McGee would like to thank Vasco for his assistance in the laboratory. C. Mayer and A. Frew are acknowledged for their help during the 40Ar/39Ar analyses of muscovite. ASC thanks FAPESP and the Australian Research Council (FT120100340) for funding. This paper forms TRaX Record #xxx. REFERENCES
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Chapter 4 The tectonic and palaeoenvironmental significance of the Alto Paraguay Group
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Chapter 4 The tectonic and palaeoenvironmental significance of the Alto Paraguay GroupTa
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-03
105
2.53
03E
-06
125
3.02
36E
-04
32.
9740
E-0
20
1157
145
97.1
00.
610.
0244
0.05
132A
1973
9D9.
4702
E-0
680
1.93
18E
-03
275
2.04
12E
-05
191.
8210
E-0
32
2.46
44E
-01
014
8140
98.7
93.
630.
4056
2.22
782A
1974
0D1.
1193
E-0
565
1.12
53E
-03
531
4.30
02E
-06
714.
1017
E-0
42
2.70
51E
-02
179
612
388
.00
0.81
0.15
641.
6600
2A19
741D
2.64
93E
-08
3028
45.
9058
E-0
389
1.73
49E
-05
201.
0873
E-0
32
9.72
48E
-02
011
0549
99.5
02.
170.
0795
0.14
172A
1974
3D1.
2488
E-0
584
9.03
92E
-03
595.
5682
E-0
59
4.24
77E
-03
11.
9505
E-0
10
641
1997
.70
8.47
0.20
240.
2375
2A19
744D
5.83
03E
-06
134
6.26
85E
-04
855
1.32
82E
-06
273
4.00
16E
-04
43.
4463
E-0
20
1037
129
94.8
00.
800.
2748
4.70
11
BS
A 08
61
Chapter 4 The tectonic and palaeoenvironmental significance of the Alto Paraguay Group
Tabl
e 1.
(con
tinue
d)
Ana
lysi
s N
ame
36A
r%
1σ37
Ar
%1σ
38A
r%
1σ39
Ar
%1σ
40A
r%
1σA
ge (M
a)±
2σ40
Ar(
r)(%
)39
Ar(
k)(%
)K
/Ca
± 2σ
2A19
555D
1.40
93E
-06
312
2.59
77E
-03
129
4.21
25E
-05
163.
1035
E-0
31
2.23
14E
-01
093
919
99.7
13.
300.
5140
1.33
062A
1955
6D4.
4722
E-0
611
99.
6953
E-0
424
81.
2736
E-0
544
1.20
48E
-03
18.
3204
E-0
20
925
3110
1.70
1.28
0.53
402.
6460
2A19
557D
7.21
94E
-06
658.
4430
E-0
433
73.
6637
E-0
514
2.26
10E
-03
11.
5765
E-0
10
909
1898
.59
2.40
1.15
197.
7734
2A19
559D
4.93
40E
-06
985.
3895
E-0
445
29.
4169
E-0
58
7.46
51E
-03
15.
2335
E-0
10
921
1299
.71
7.93
5.95
6353
.824
22A
1956
0D6.
3775
E-0
654
4.95
99E
-05
6689
2.45
33E
-05
241.
3663
E-0
32
1.15
03E
-01
010
4932
98.3
41.
4511
.845
815
84.7
231
2A19
561D
7.69
65E
-06
816.
2964
E-0
438
05.
8248
E-0
57
4.65
06E
-03
14.
0955
E-0
10
1095
1499
.45
4.94
3.17
5724
.142
62A
1956
2D1.
7391
E-0
630
71.
4326
E-0
320
45.
6776
E-0
514
3.93
93E
-03
12.
7298
E-0
10
914
1299
.85
4.18
1.18
214.
8347
2A19
564D
5.62
07E
-07
715
3.39
73E
-03
763.
4650
E-0
514
1.81
83E
-03
11.
2775
E-0
10
923
2299
.91
1.93
0.23
050.
3519
2A19
565D
9.39
99E
-06
492.
0284
E-0
312
81.
2309
E-0
557
1.73
62E
-03
11.
2751
E-0
10
939
2197
.66
1.85
0.36
840.
9447
2A19
566D
1.03
49E
-05
431.
4718
E-0
328
61.
3751
E-0
532
1.29
65E
-03
11.
4213
E-0
10
1272
2797
.91
1.38
0.37
852.
1680
2A19
569D
2.33
18E
-06
304
2.18
38E
-03
163
1.54
86E
-05
441.
0532
E-0
31
1.33
41E
-01
014
2040
99.3
41.
120.
2077
0.67
772A
1957
0D8.
6296
E-0
764
92.
4875
E-0
315
71.
5092
E-0
571
2.86
70E
-03
13.
9848
E-0
10
1520
1599
.88
3.05
0.49
591.
5527
2A19
571D
7.06
41E
-07
839
1.74
27E
-03
227
1.90
23E
-05
392.
0781
E-0
31
2.13
19E
-01
012
3124
99.9
72.
210.
5124
2.33
092A
1957
2D2.
0279
E-0
628
52.
5881
E-0
313
73.
9044
E-0
525
3.24
75E
-03
03.
7343
E-0
10
1332
1399
.78
3.45
0.53
991.
4846
2A19
574D
6.52
12E
-06
742.
0873
E-0
319
61.
3861
E-0
554
2.26
49E
-03
02.
5416
E-0
10
1318
1410
0.70
2.41
0.46
691.
8316
2A19
575D
5.74
63E
-06
113
1.10
92E
-03
342
1.53
43E
-05
512.
0351
E-0
32
1.44
57E
-01
094
230
101.
252.
160.
7886
5.39
842A
1957
6D1.
6911
E-0
634
74.
2353
E-0
310
83.
7864
E-0
525
3.44
49E
-03
13.
8632
E-0
10
1308
1799
.78
3.66
0.35
010.
7581
2A19
579D
1.61
54E
-07
3285
7.85
13E
-04
470
3.15
37E
-05
211.
8193
E-0
31
1.28
83E
-01
093
124
100.
011.
930.
9961
9.36
432A
1958
0D1.
2287
E-0
646
07.
8572
E-0
442
63.
1960
E-0
529
2.44
63E
-03
12.
2350
E-0
10
1128
2799
.81
2.60
1.33
9111
.415
32A
1958
1D8.
8558
E-0
772
71.
3051
E-0
326
93.
9001
E-0
517
2.90
13E
-03
12.
6120
E-0
10
1116
2299
.86
3.08
0.95
625.
1470
2A19
582D
6.93
42E
-06
724.
7081
E-0
382
5.86
55E
-05
134.
7158
E-0
31
3.53
25E
-01
096
915
99.5
35.
000.
4304
0.70
952A
1958
4D4.
2432
E-0
615
61.
0214
E-0
334
31.
6644
E-0
47
1.31
88E
-02
18.
9294
E-0
10
899
1010
0.15
14.0
05.
5514
38.0
856
2A19
746D
5.75
61E
-06
841.
6905
E-0
325
62.
8895
E-0
517
2.77
75E
-03
12.
7995
E-0
10
1219
1510
0.56
2.95
0.70
683.
6141
2A19
747D
6.09
69E
-08
1256
13.
8434
E-0
372
2.73
93E
-05
121.
8059
E-0
31
2.10
65E
-01
013
5131
100.
141.
910.
2017
0.29
082A
1974
8D9.
5870
E-0
752
71.
2318
E-0
333
55.
3235
E-0
513
5.05
53E
-03
13.
5651
E-0
10
927
1599
.89
5.37
1.76
5111
.838
42A
1974
9D1.
6229
E-0
633
53.
7369
E-0
394
1.66
86E
-05
341.
8328
E-0
31
1.29
85E
-01
093
125
100.
131.
950.
2112
0.39
652A
1975
2D2.
5391
E-0
622
89.
4659
E-0
382
2.37
43E
-05
342.
9119
E-0
31
3.42
77E
-01
013
5516
99.9
93.
100.
1326
0.21
762A
1975
3D7.
2381
E-0
690
1.56
54E
-04
4552
3.18
01E
-05
242.
6361
E-0
31
2.99
69E
-01
013
1728
99.2
72.
807.
2415
659.
2694
2A19
754D
1.86
53E
-07
3800
5.46
02E
-03
135
2.83
85E
-05
233.
6613
E-0
30
4.93
67E
-01
014
8912
99.9
03.
890.
2886
0.77
972A
1975
5D5.
2625
E-0
611
78.
4628
E-0
391
2.57
85E
-05
322.
5514
E-0
31
1.94
09E
-01
097
325
98.8
22.
720.
1300
0.23
72
1A18
396/
97D
1.02
65E
-05
148
2.46
28E
-03
212.
7281
E-0
536
1.62
12E
-03
27.
2418
E-0
20
667
68-
-0.
2275
0.14
341A
1841
8/19
D2.
6072
E-0
555
7.79
34E
-04
743.
7576
E-0
533
2.88
36E
-03
12.
0632
E-0
10
1027
72-
-0.
9724
2.93
91
BR
Z 09
BD
M 0
9
62
Chapter 4 The tectonic and palaeoenvironmental significance of the Alto Paraguay GroupTa
ble
1. (c
ontin
ued)
Ana
lysi
s N
ame
36A
r%
1σ37
Ar
%1σ
38A
r%
1σ39
Ar
%1σ
40A
r%
1σA
ge (M
a)±
2σ40
Ar(
r)(%
)39
Ar(
k)(%
)K
/Ca
± 2σ
1A18
420D
8.15
20E
-06
947.
7481
E-0
540
31.
8458
E-0
545
2.01
35E
-03
11.
6337
E-0
10
1045
3110
1.48
100.
0011
.174
590
.059
31A
1847
7/79
D1.
3534
E-0
582
1.40
89E
-03
391.
8820
E-0
564
2.83
10E
-03
11.
2658
E-0
10
625
51-
-0.
7321
0.50
341A
1845
8D2.
4518
E-0
660
61.
3264
E-0
442
81.
9831
E-0
554
1.69
04E
-03
11.
4355
E-0
10
1074
5510
0.52
100.
005.
4797
46.8
613
1A18
460/
61D
4.08
47E
-06
584
1.96
14E
-04
437
9.32
49E
-07
2335
1.43
38E
-03
26.
3809
E-0
21
612
107
--
1.36
0012
.890
01A
1845
7D2.
4794
E-0
660
13.
6587
E-0
416
02.
2963
E-0
545
1.27
21E
-03
25.
8551
E-0
20
664
8610
1.32
100.
001.
4948
4.78
821A
1845
5/56
D1.
7667
E-0
512
22.
8479
E-0
428
91.
3454
E-0
510
56.
5130
E-0
43
5.36
45E
-02
111
0116
3-
-0.
1800
0.78
001A
1843
8/39
D7.
6303
E-0
618
51.
9246
E-0
436
13.
5329
E-0
624
92.
1228
E-0
31
8.48
53E
-02
058
338
--
0.16
000.
8000
1A18
436/
37D
5.62
86E
-07
2429
7.16
99E
-04
92-7
.570
8E-0
613
71.
6994
E-0
32
7.66
14E
-02
064
760
--
0.81
001.
5200
1A18
527/
28D
3.18
11E
-06
351
1.12
03E
-03
584.
8708
E-0
634
61.
1092
E-0
32
5.03
93E
-02
063
170
--
0.42
920.
4827
1A18
529/
30D
1.71
72E
-06
686
8.73
32E
-04
831.
9777
E-0
585
1.55
30E
-03
26.
7182
E-0
20
608
55-
-0.
7100
1.07
041A
1853
2/3D
1.82
79E
-05
781.
1535
E-0
470
73.
4593
E-0
554
2.28
66E
-03
21.
0446
E-0
10
632
40-
-0.
7000
5.60
002A
1950
7D3.
5572
E-0
615
41.
7213
E-0
316
82.
1178
E-0
523
1.29
90E
-03
25.
6111
E-0
20
630
3910
1.63
100.
000.
3248
1.09
152A
1950
8D1.
0401
E-0
575
5.37
00E
-03
751.
4434
E-0
540
1.00
34E
-03
24.
5683
E-0
20
605
6092
.21
100.
000.
0807
0.12
152A
1950
9D1.
8908
E-0
524
2.84
64E
-03
116
2.24
03E
-05
302.
0199
E-0
31
1.41
61E
-01
089
218
95.8
410
0.00
0.30
550.
7107
2A19
511D
1.32
52E
-07
3056
2.48
50E
-03
110
1.76
22E
-05
458.
6178
E-0
41
3.79
17E
-02
163
638
100.
6610
0.00
0.14
880.
3259
2A19
512D
4.25
55E
-06
218
8.42
28E
-03
312.
3550
E-0
532
1.40
17E
-03
17.
5520
E-0
20
729
4897
.38
100.
000.
0719
0.04
392A
1951
3D2.
9074
E-0
627
81.
2509
E-0
318
44.
4034
E-0
514
1.93
20E
-03
18.
5565
E-0
20
629
3498
.86
100.
000.
6645
2.44
062A
1951
5D2.
8972
E-0
614
25.
1148
E-0
366
2.92
86E
-05
161.
8325
E-0
31
8.19
67E
-02
063
918
99.4
710
0.00
0.15
370.
2033
2A19
516D
5.12
49E
-06
415.
8344
E-0
340
5.87
80E
-06
413.
1128
E-0
43
1.32
79E
-02
170
159
115.
2210
0.00
0.02
260.
0182
2A19
720D
4.18
67E
-06
191
2.39
90E
-03
352
1.51
87E
-05
361.
0652
E-0
31
4.47
80E
-02
059
759
97.6
611
.39
0.19
061.
3424
2A19
721D
2.63
92E
-06
276
8.62
38E
-04
986
2.33
39E
-05
352.
0426
E-0
31
9.35
84E
-02
064
931
99.0
821
.88
1.01
8820
.080
92A
1972
2D1.
4060
E-0
556
3.43
88E
-04
2636
1.17
50E
-05
521.
0810
E-0
31
4.88
94E
-02
059
959
91.3
511
.58
1.35
2171
.274
72A
1972
3D3.
6262
E-0
622
63.
8916
E-0
321
91.
8163
E-0
528
1.43
94E
-03
16.
4512
E-0
20
636
4698
.83
15.3
80.
1587
0.69
532A
1972
5D5.
1578
E-0
614
71.
0082
E-0
287
1.06
14E
-05
461.
1901
E-0
31
5.43
68E
-02
062
551
95.6
012
.82
0.05
1 10.
0889
2A19
726D
2.99
46E
-06
318
1.22
90E
-03
714
1.18
05E
-05
571.
5073
E-0
31
6.33
31E
-02
061
650
101.
5716
.13
0.52
717.
5318
2A19
727D
1.75
26E
-06
512
1.53
90E
-03
565
9.62
48E
-06
641.
0114
E-0
32
4.72
11E
-02
067
269
101.
3810
.82
0.28
233.
1877
2A19
677D
5.10
45E
-06
976.
7497
E-0
477
44.
8231
E-0
511
4.36
68E
-03
11.
8051
E-0
10
595
1699
.12
8.59
2.78
2243
.092
72A
1967
8D2.
1549
E-0
626
58.
4614
E-0
372
3.67
43E
-05
272.
8051
E-0
31
2.03
05E
-01
094
017
99.3
35.
530.
1429
0.20
682A
1967
9D4.
3849
E-0
796
22.
5035
E-0
321
43.
1426
E-0
517
2.73
68E
-03
19.
9504
E-0
20
539
1810
0.34
5.38
0.46
982.
0129
2A19
681D
3.54
28E
-07
1457
3.21
02E
-03
169
2.23
18E
-05
221.
3776
E-0
31
5.57
51E
-02
059
333
100.
672.
700.
1842
0.62
222A
1968
2D2.
1390
E-0
621
41.
9098
E-0
328
41.
0380
E-0
557
5.49
97E
-04
36.
1160
E-0
20
1289
7098
.69
1.08
0.12
410.
7041
2A19
683D
5.73
45E
-06
925.
2729
E-0
310
01.
8401
E-0
528
1.30
18E
-03
14.
9995
E-0
20
574
3310
2.54
2.57
0.10
650.
2122
2A19
686D
2.46
23E
-06
122
6.74
60E
-03
811.
4119
E-0
538
1.20
26E
-03
15.
4511
E-0
20
647
2310
0.31
2.37
0.07
700.
1250
BD
M 1
2
63
Chapter 4 The tectonic and palaeoenvironmental significance of the Alto Paraguay Group
Tabl
e 1.
(con
tinue
d)
Ana
lysi
s N
ame
36A
r%
1σ37
Ar
%1σ
38A
r%
1σ39
Ar
%1σ
40A
r%
1σA
ge (M
a)±
2σ40
Ar(
r)(%
)39
Ar(
k)(%
)K
/Ca
± 2σ
2A19
687D
2.03
17E
-06
361
3.29
69E
-03
197
4.89
12E
-05
113.
1165
E-0
31
1.16
42E
-01
054
922
99.7
26.
120.
4062
1.59
982A
1968
8D1.
1804
E-0
635
92.
2312
E-0
324
32.
6218
E-0
529
2.30
46E
-03
19.
9214
E-0
20
620
1799
.83
4.53
0.44
382.
1598
2A19
689D
5.54
87E
-06
831.
0185
E-0
356
33.
1660
E-0
520
2.28
34E
-03
18.
6950
E-0
20
549
2097
.99
4.49
0.96
4310
.865
32A
1969
1D8.
3641
E-0
749
37.
0643
E-0
384
2.58
34E
-05
231.
5079
E-0
31
5.51
06E
-02
053
124
98.4
72.
980.
0921
0.15
452A
1969
2D2.
0038
E-0
626
01.
1045
E-0
359
41.
8938
E-0
533
1.39
01E
-03
16.
6742
E-0
20
676
3099
.24
2.73
0.54
096.
4278
2A19
693D
4.29
08E
-08
8214
1.72
13E
-03
388
2.62
93E
-05
181.
7534
E-0
32
7.40
68E
-02
061
224
100.
183.
450.
4377
3.39
242A
1969
4D3.
5627
E-0
611
01.
2378
E-0
354
72.
2316
E-0
516
1.15
65E
-03
14.
2935
E-0
20
560
3210
2.72
2.27
0.40
144.
3879
2A19
696D
2.83
60E
-07
2009
5.01
30E
-03
120
2.18
79E
-05
231.
6515
E-0
32
6.22
85E
-02
054
933
99.1
83.
250.
1420
0.34
182A
1969
7D5.
5570
E-0
677
1.01
62E
-03
573
5.58
22E
-06
946.
5428
E-0
42
2.48
86E
-02
052
458
92.9
91.
290.
2772
3.17
482A
1969
8D4.
5284
E-0
611
43.
2457
E-0
417
275.
7442
E-0
512
4.06
42E
-03
11.
4718
E-0
10
539
1310
0.90
7.99
5.38
4818
5.98
352A
1969
9D1.
1435
E-0
638
69.
1827
E-0
459
63.
3085
E-0
520
1.83
90E
-03
19.
0201
E-0
20
695
2110
0.46
3.61
0.86
0810
.261
42A
1970
1D3.
3514
E-0
913
7429
7.65
38E
-04
836
2.02
33E
-05
242.
3088
E-0
31
3.96
54E
-01
017
4934
100.
024.
541.
2968
21.6
697
2A19
702D
4.89
10E
-06
923.
8461
E-0
315
49.
3168
E-0
649
6.29
95E
-04
22.
6764
E-0
20
650
6010
6.67
1.23
0.07
010.
2163
2A19
703D
7.79
49E
-06
492.
9005
E-0
420
493.
5431
E-0
616
76.
5122
E-0
43
2.92
43E
-02
168
655
108.
041.
280.
9651
39.5
409
2A19
704D
2.01
61E
-07
2021
6.96
15E
-04
849
7.93
96E
-06
547.
9657
E-0
41
2.96
62E
-02
054
843
100.
001.
570.
4923
8.35
722A
1970
6D6.
5561
E-0
749
13.
6087
E-0
416
041.
7538
E-0
523
1.13
40E
-03
15.
1410
E-0
20
650
2610
0.44
2.23
1.35
1043
.342
52A
1993
1D2.
5669
E-0
636
41.
3783
E-0
361
32.
3148
E-0
529
1.92
27E
-03
17.
2968
E-0
20
551
3998
.79
3.78
0.60
017.
3573
2A19
932D
5.95
58E
-06
142
1.53
62E
-03
507
9.04
01E
-06
729.
3056
E-0
41
3.78
80E
-02
056
572
94.9
61.
830.
2608
2.64
602A
1993
3D2.
7582
E-0
633
86.
2082
E-0
313
61.
1323
E-0
552
1.10
72E
-03
25.
0140
E-0
20
648
6510
0.60
2.19
0.07
700.
2090
2A19
934D
4.05
65E
-06
212
2.78
82E
-03
285
2.44
43E
-05
361.
8348
E-0
32
8.51
44E
-02
065
539
98.8
53.
600.
2827
1.61
182A
1993
6D3.
2488
E-0
726
971.
5828
E-0
349
91.
5979
E-0
539
1.28
87E
-03
16.
0945
E-0
20
674
5210
0.38
2.53
0.34
983.
4942
2A19
937D
3.49
17E
-06
270
6.08
39E
-04
1285
8.94
15E
-06
511.
2033
E-0
31
5.13
31E
-02
060
661
98.0
72.
370.
8502
21.8
525
2A19
938D
2.76
33E
-06
354
2.83
60E
-03
304
5.76
35E
-06
779.
6808
E-0
42
6.87
13E
-02
091
972
98.4
51.
910.
1471
0.89
34
Chapter 5: Age and Provenance of the Cryogenian to Cambrian passive margin to foreland basin sequence of the northern Paraguay Belt, Brazil.
This chapter is under review as:McGee, B., Collins, A.S. and Trindade, R.I.F., Under Review. Age and Provenance of the Cyrogenian to Cambrian passive margin to foreland basin sequence of the northern Paraguay Belt, Brazil. Bulletin of the Geological Society of America.
67
Chapter 5 Age and provenance of the northern Paraguay Belt
Age and Provenance of the Cryogenian to Cambrian passive margin to foreland basin sequence of the northern Paraguay Belt, Brazil
Ben McGee1, Alan S. Collins1 and Ricardo I.F. Trindade2
1Centre for Tectonics, Resources and eXploration (TRaX), School of Earth and Environmental Sciences, B09, Mawson Building, The University of Adelaide, SA 5005, Australia.2Departamento de Geofísica, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Rua do Matão, 1226, 05508-090, São Paulo, Brazil.
ABSTRACT
The Paraguay Belt in central South America developed in response to the collision between the Amazonian Craton, the Rio Apa Block, the São Francisco Craton and the Paranapanema Block. The alleged ‘Brasiliano’ age (~620 Ma) of orogenesis has recently been questioned by palaeomagnetic and radioisotopic ages that indicate the closing stages of orogenesis occurred well into the Cambrian. The timing of deposition and source areas for these sedimentary rocks overlying the Amazonian Craton are investigated here using integrated U-Pb and Hf isotope data of detrital zircons from within this sequence. 742 detrital zircon LA-ICPMS U-Pb ages were analysed from samples taken from the base to the top of this sedimentary succession. Maximum depositional ages from the uppermost part of this sequence of rocks, the Diamantino Formation, indicate that final sedimentation began no earlier than 527 Ma. Given that zircon inheritance in these rocks continues up until this age and that known Amazonian Craton ages are older than ~950 Ma we consider other potential sources for these sediments. This is achieved by integrating the U-Pb detrital zircon data with Hf isotopic data from these zircons that have εHf values ranging from -18 to 12. The εHf signature is consistent with a predominantly Amazonian source until the early-Neoproterozoic at which point the signal becomes significantly more evolved. These data, when combined with other evidence
discussed here, are consistent with an ocean to the east of the present-day Amazonian Craton that didn’t close until the Cambrian.
INTRODUCTION
Reconstructing the palaeogeography and the timing of formation of the Palaeozoic supercontinent Gondwana has received significant attention in the literature for many decades (e.g. Collins and Pisarevsky, 2005; Stern, 1994). A fundamental requirement of these reconstructions is that they fulfill available geological constraints, including correlations based on ages of events in neighbouring orogenic belts, palaeomagnetic constraints and relationships between sedimentary, geochemical and temporal provenance patterns. Early Gondwana reconstruction models of a collision between large fragments of east and west Gondwana at ~650 Ma (Stern, 1994) have evolved to incorporate current evidence that identify a network of suturing events between relatively small Neoproterozoic continents that amalgamated to form Gondwana during the Ediacaran and Cambrian (e.g. Collins and Pisarevsky, 2005; Meert, 2003; Pisarevsky et al., 2008). The Paraguay Belt in Brazil is part of this network of Gondwana-forming orogens that for some time has been considered as ‘Brasiliano’ (ca. 940 – 620 Ma) in age (Cordani et al. 2009). This interpretation is based upon ages from the western border of the São Francisco Craton and implies that amalgamation of western Gondwana occurred at around 620 Ma.
This hypothesis was brought
into question by the presentation of a palaeomagnetic pole from carbonates of the Araras Group, from the northern Paraguay Belt, that indicated Amazonia was at low latitudes at the beginning of the Ediacaran (Trindade et al., 2003). This finding suggested that Amazonia was separated from proto-Gondwana by a large ocean—the Clymene Ocean—up until the Cambrian (Trindade et al., 2006). In this model a major orogenic belt encompassing the Araguaia, Paraguay and Pampean belts represented the suture zone of this ocean and the final amalgamation of Gondwana. This proposition promoted interest in these regions and several studies incorporating palaeomagnetic, Sm-Nd, geochronological, sedimentary and stratigraphic methodologies have since followed.
In this study we present a large U-Pb data set to complement these previous works in order to better understand the provenance of these sediments. In addition to these temporal constraints we present accompanying Lu-Hf isotope data that provide information about the crustal evolution of the source region and allow for comparisons between sedimentary packages. We go on to discuss the implications of these finding on the tectonic and palaeogeographic reconstructions for Amazonia in the context of Gondwana amalgamation.
REGIONAL SETTING
The Paraguay Belt is located in central South America (Figure 1) and marks the boundary between the Amazon, São Francisco, Paranapanema, Rio Apa and Rio de la Plata cratons. It comprises
68
Chapter 5 Age and provenance of the northern Paraguay Belt
metamorphosed Neoproterozoic and Cambrian sedimentary strata that were deposited in a passive margin environment (Alvarenga and Trompette, 1992). These metasedimentary and sedimenatary rocks are divided into the older pelites, diamictites and siliciclastics of the Cuiabá Group in the core of the orogen (Barros et al., 1982), diamictites of the Puga Formation, carbonates of the Araras Group and siliciclastics of the upper Alto Paraguay Group. While the nature of the contact between the Cuiabá Group and Puga Formation not well understood do to non-exposure, recent interpretations describe the Puga diamictite as the proximal ‘shelf’ facies of the Cuiabá Group
(Alvarenga et al., 2009). The age of the youngest detrital zircon in the Puga Formation (706 ± 9 Ma; Babinski et al., In press). The δ13C (5.0‰) and the 87Sr/86Sr (0.7080) ratios from carbonates directly overlying the diamictites (Nogueira et al., 2003), suggest that these represent the ~635 Ma end-Cryogenian glaciation.
In the northern Paraguay Belt the stratigraphic framework of the Alto Paraguay Group was first described by Almeida (1964) who divided it into the ~1600 m sands, silts and shale of the Raizama Formation, ~900 m of shale, silts and sandstones of the Sepotuba Formation and ~600 m of Diamantino Formation rhythmites
and sandstones. More recently Alvarenga et al. (2007) described a new unit, the Serra Azul Formation, in between carbonates of the Araras Group and the siliclastics of the Alto Paraguay Group. The basal part of this formation is composed of a glaciogenic diamictite containing multiply striated sandstone clasts (Alvarenga et al., 2007) and striated, polished and bullet-shaped mudstone clasts (McGee et al., Under Review), which is overlain by a transgressive package of interlayered silts and fine sands. The siltstone and sandstone of the upper Alto Paraguay Group were shed off rising topography—the Paraguay orogen—in response to collision between the Amazonian
Figure 1 - Author: Ben McGee , Extension: .pdf
Figure 1. Geological map showing lithostratigraphic relationships within the northern Paraguay Belt. Modified from CPRM Cuiabá 1:1000000 map sheet (Barros et al., 1982). Stars indicate the location of samples for geochronological analysis; 1: BDM-01 and BRZ-02; 2: BRZ-02; 3: BSA-07, BRZ-15; 4: BPUG-02, BSA-20, BST-24.
A NOTE:
This figure/table/image has been removed to comply with copyright regulations. It is included in the print copy of the thesis held by the University of Adelaide Library.
69
Chapter 5 Age and provenance of the northern Paraguay Belt
Craton, the São Francisco Craton and the Paranapanema Block between ~540–520 Ma (Bandeira et al., 2011). The termination of orogenesis was marked by intrusion of post-orogenic granites into the base of these sediments at ~518 Ma (McGee et al., 2012).
ANALYTICAL METHODS
Zircon U-Pb LA-ICPMS analysis
The location of samples collected for geochronological analysis are shown in Figure 1. These samples were prepared using the methods described in McGee et al. (2012). U–Pb fractionation was corrected using the GEMOC GJ-1 zircon standard (TIMS normalisation data 207Pb/206Pb = 608.3 Ma, 206Pb/238U = 600.7 Ma and 207Pb/235U = 602.2 Ma, (Jackson et al., 2004)) and accuracy was checked using the recognised zircon standard ‘Plesovice’ with a 206Pb/238U = 337.13 ± 0.37 Ma (Slama et al., 2008). Data reduction was performed using GLITTER (Van Achterbergh et al., 2001). The average normalised ages for GJ-1 during the course of this study were 608.6 Ma ± 9.2 (2s) Ma (MSWD = 0.030), 601.4 ± 2.4 (2s) Ma (MSWD = 0.094) and 602.7 ± 2.3 (2s) Ma (MSWD = 0.058) for the 207Pb/206Pb, 206Pb/238U and 207Pb/235U ratios respectively (n = 362). The average normalised 206Pb/238U age for Plesovice is 337.9 ± 1.3 (2s) Ma (MSWD = 0.057; n = 139). Probability density plots were constructed using Isoplot version 3.0 (Ludwig, 2003).
Zircon Hf isotopic analysis
The same zircon mount discs prepared for U-Pb isotopic analysis were used for Hf. Hafnium analyses were conducted via Laser Ablation Multicollector Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICPMS) at the University of Adelaide and CSIRO’s joint facility at the Waite campus in South Australia. Ablation was achieved using a New Wave UP-193 Excimer laser (193 nm) using a spot size of 50 μm; frequency of 4 Hz; 4 ns pulse
length and an intensity of ∼8–10 J/cm2. Hafnium ablation pits targeted the same textural CL zone as the corresponding U-Pb ablation pit and were made in a helium atmosphere and subsequently mixed with argon upstream of the ablation cell. The attached Thermo-Scientific Neptune Multi Collector ICP-MS measured 171Yb, 173Yb, 175Lu, 176Hf, 177Hf, 178Hf, 179Hf and 180Hf on Faraday detectors with 1011 Ω amplifiers. 500 sweeps of this isotope array were made, each of 0.262 seconds length, for a total analysis time of 131 seconds, including a 30 second Helium gas background measurement. Hf Mass bias was corrected using an exponential fractionation law with a stable 179Hf/177Hf ratio of 0.7325. Yb and Lu isobaric interferences on 176Hf were corrected using the methods of (Woodhead et al., 2004). 176Yb interference on 176HF was corrected through direct measurement of Yb fractionation using measured 171Yb/173Yb with the Yb isotopic values of (Segal et al., 2003). The applicability of these values were verified by analysing JMC 475 Hf solutions doped with varying levels of Yb with interferences up to 176Yb/177Hf = ∼0.5. Lu isobaric interference on 176Hf was corrected using a 176Lu/175Lu ratio of 0.02655 (Vervoort et al., 2004) assuming the same mass bias behaviour of as Yb.
Set-up of the system prior to ablation sessions was conducted using analysis of JMC475 Hf solution and an AMES Hf solution. Confirmation of accuracy of the technique for zircon analysis was monitored using a combination of the Plesovice, Mudtank and QGNG standards. The average value for Plesovice for the analytical session was 0.282471 ± 0.000017 (2σ; n = 24), which statistically overlaps the published value of 0.282482 ± 0.000013 (2σ; Slama et al., 2008). TDM and TDM crustal were calculated using 176Lu decay constant after (Scherer et al., 2001). TDM crustal was calculated using the methods of (Griffin et al., 2000) with an average crustal composition of 176Lu/177Hf = 0.015.
RESULTS
Zircon U-Pb LA-ICPMS isotopic results
Eight samples were selected for geochronological analysis that gave the broadest temporal range, from the base of the Puga Formation to the top of the Alto Parauay Group (Figure 1). Sample BPUG-02 is a green/grey diamictite with a coarse matrix from the Puga Formation. Samples BSA-07 and BSA-20 are from the Serra Azul Formation and are a brown/maroon diamictite with a fine silty matrix and a pale green diamictite with a fine sandy matrix respectively. Samples BRZ-01, BRZ-02 & BRZ-15 are medium and coarse arenites with lenses of matrix supported pebble conglomerate from the Raizama Formation. Sample BST-24 is from the Sepotuba Formation and is a deep red/purple coarse-grained arenite. BDM-01 is from the top of the sequence—the Diamantino Formation—and is a mature, white coarse sandstone.
Geochronological data are presented in Figures 2 and 3 and analytical data are provided in supplemental Table 1. Ages are reported using the 206Pb/238U ratio, all errors are quoted at the 2 sigma (2σ) level and weighted averages are at 95 % confidence. Laser-ablation spots targeted oscillatory-zoned magmatic cores where possible (Figure 4).
Age Estimates
BDM-01 (Mature pale arenite)98 LA-ICPMS analyses of 96
zircon grains were collected from sample BDM-01 (Table 1), targeting moderately luminescent cores and rims, in some cases with oscillatory zoning (Figure 4a). BDM-01 is the only sample that shows Cambrian zircon inheritance (Figure 3), with the youngest grain at 527 Ma (Figure 2). The majority of other grains are Mesoproterozoic and another peak in the Palaeoproterozoic (Figure 3).
BST-24 (Deep purple coarse grained arenite)
70
Chapter 5 Age and provenance of the northern Paraguay Belt
99 LA-ICPMS analyses of an equal number of zircon grains were collected from sample BRZ-24 (Table 1), targeting moderately luminescent, oscillatory-zoned magmatic growth regions (Figure 4b). All analyses are highly concordant (Figure 2) and lie between 615 Ma and 1950 Ma (Figure 3).
BRZ-15 (Coarse grained arenite)81 LA-ICPMS analyses of an
equal number of zircon grains were collected from sample BRZ-15 (Table 1), targeting moderate- to highly-luminescent oscillatory-zoned magmatic regions (Figure 4c). The analyses are predominantly concordant (Figure 2) and lie between 950 Ma and 1800 Ma (Figure 3) with one large peak at 1550 Ma.
BRZ-01 (Medium grained arenite)82 LA-ICPMS analyses of
an equal number of zircon grains were collected from sample BRZ-01 (Table 1), targeting moderately luminescent, oscillatory-zoned magmatic growth regions (Figure 4d). The analyses are generally concordant (Figure 2) and mainly
spread between 900 Ma and 1560 Ma with two outliers, one at 635 Ma and the other at 1984 Ma (Figure 3).
BRZ-02 (Coarse grained arenite)86 LA-ICPMS analyses of
85 zircon grains were collected from sample BRZ-02 (Table 1), targeting moderately luminescent, oscillatory-zoned magmatic growth regions (Figure 4e). The majority of analyses are highly concordant (Figure 2) and lie between 900 Ma and 1850 Ma (Figure 3).
BSA-07 (Green/grey diamictite)105 LA-ICPMS analyses of 103
zircon grains were collected from sample BSA-07 (Table 1), targeting moderate- to highly-luminescent oscillatory-zoned magmatic growth zones (Figure 4f). The majority of grains are concordant with a small number of discordant grains with no obvious common-Pb or Pb-loss trend (Figure 2). The three youngest analyses are grouped around 650 Ma, the youngest at 646 Ma, with the majority of grains spread between 900 and 1700 Ma (Figure 3). Three prominent peaks occur at 1860 Ma, 1975 Ma and 2090 Ma respectively.
BSA-20 (Green/grey diamictite)98 LA-ICPMS analyses of
97 zircon grains were collected from sample BSA-20 (Table 1), targeting moderately luminescent, oscillatory-zoned magmatic growth regions (Figure 4g). The majority of samples lie along concordia (Figure 2) from 665 Ma to 2050 Ma (Figure 3).
BPUG-02 (Red/brown to purple Diamictite)
93 LA-ICPMS analyses of an equal number of zircon grains were collected from sample BPUG-02 (Table 1), targeting dark to moderately luminescent oscillatory-zoned magmatic growth regions (Figure 4h). The analyses are highly to moderately concordant, with a slight spread of data below concordia (Figure 2). Two main clusters of data are apparent; at 1050 Ma and spread between 1400 Ma and 1800 Ma (Figure 3).
Zircon Hf isotopic results
Hf istopic results are presented in an εHf vs. time plot in Figure 5 and the corresponding data are
200
BDM-01Areniten = 98
206Pb/238U
2200
1800
1400
1000
600
200
BST-24Areniten = 99
2200
1800
1400
1000
600
200
BRZ-15Areniten = 81
2200
1800
1400
1000
600
200
BRZ-01Areniten = 82
2200
1800
1400
1000
600
200
BRZ-02Areniten = 86
2200
1800
1400
1000
600
200
BSA-07Diamictiten = 105
2200
1800
1400
1000
600
200
BSA-20Diamictiten = 98
0.0
0.1
0.2
0.3
0.4
0 2 4 6 8207Pb/235U
U20
6 Pb/23
8
2200
1800
1400
1000
600
200
BPUG-02Diamictiten = 93
Cam
bria
nEd
iaca
ran
Cryo
geni
anTo
nian
Figure 2 - Colour for web only. Author: Ben McGee, Extension: .pdf
Figure 2. Concordia plots for U-Pb detrital zircon LA-ICPMS data from the northern Paraguay Belt.
71
Chapter 5 Age and provenance of the northern Paraguay Belt
BPUG-02Diamictite
n = 93
BSA-20Arenite
n = 99
BSA-07Diamictite
n = 105
0.000
0.001
0.002
0.003
Pro
bab
ility
Den
sity
0.000
0.001
0.002
0.003
0.000
0.001
0.002
0.003
0.000
0.001
0.002
0.003
0.004
0.000
0.001
0.002
0.003
0.004
0.000
0.001
0.002
0.003
0.000
0.001
0.002
0.003
0.004
0.005
0.000
0.001
0.002
0.003
0.004
BDM-01Arenite
n = 99
BRZ-02Arenite
n = 86
BRZ-15Arenite
n = 81
Age (Ma)
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
BRZ-01Arenite
n = 82
BST-24Arenite
n = 99
Figure 3 - Probability Density Plots. Author: Ben McGee, Extension: .pdfformations and of the total 255 zircons that were analysed, 240 analyses are plotted, limited to <10% age discordancy. By sample, 42 grains were analysed and 33 are plotted for BDM-01; 35 grains were analysed and 34 are plotted for BPUG-02; all grains analysed (32) are plotted for BRZ-01; all grains analysed (10) are plotted for BRZ-02; all grains analysed (35) are plotted for BRZ-15; all grains analysed (38) are plotted for BST-24; 23 grains were analysed and 22 are plotted for BSA-07 and 40 grains were analysed and 36 are plotted for BSA-20.
The zircons from sample BRZ-01 with ages between 1984 and 636 Ma have εHf values between -4 and +7. The zircons from sample BRZ-02 with ages between 1556 and 937 Ma have εHf values between -2 and +5. The zircons from sample BRZ-15 with ages between 1818 and 929 Ma have εHf values between -6 and +11. The zircons from sample BST-24 with ages between 1916 and 6115 Ma have εHf values between -8 and +6. The zircons from sample BSA-20 with ages between 1863 and 653 Ma have εHf values between -22 and +7. The zircons from sample BSA-07 with ages between 1542 and 651 Ma have εHf values between -8 and +6. The zircons from sample BDM-01 with ages between 1950 and 528 Ma have εHf values between -24 and +27. The zircons from sample BPUG-02 with ages between 1975 and 968 Ma have εHf values between -14 and +5.
Crustal model ages were calculated for each zircon assuming average continental crust with 176Lu/177Hf of 0.0015 as the zircon grain growth reservoir. Based on this crustal model, an age range of 1.4 Ga to 2.9 Ga is obtained for this package of sediments, represented by the envelope drawn on Figure 5. Overall the compilation of εHf(t) data for all formations are widely dispersed. The data begin with a more evolved signal in the late-Palaeoproterozoic, which gradually becomes more juvenile through most of the Mesoproterozoic after which point in time the signal
becomes much more evolved until 527 Ma.
DISCUSSION
U-Pb isotopic age constraints and maximum depositional ages
The U-Pb data reported here complement recent detrital muscovite 40Ar–39Ar analyses (McGee et al., submitted) by providing constraints on source regions and recognising the age of higher temperature events in the northern Paraguay Belt. The maximum depositional ages presented here are based on the ages of the youngest detrital zircon grain for each respective formation.
The U-Pb data presented here for the Puga Formation show only post-Cryogenian inheritance (>918 Ma) and do not improve the maximum depositional age of 706 Ma provided by Babinski et al. (In press). Analyses of the glaciogenic Serra Azul Formation give a maximum depositional age of 646 Ma. This age constraint means that the Serra Azul Formation is permissibly Marinoan (~635 Ma) or Gaskiers (~582 Ma) in age. Given that the Serra Azul Formation diamictite lies stratigraphically above a supposed Marinoan cap carbonate (Babinski et al., 2006; Nogueira et al., 2003) several authors have correlated the Serra Azul diamictite with the ~582 Ma Gaskiers glaciation (Alvarenga et al., 2007; McGee et al., Under Review). The maximum depositional ages of the Raizama and Sepotuba formations are constrained by the youngest analysed grains at 635 and 615 Ma respectively. The youngest analysed zircon from the Diamantino Formation is 527 Ma, which we interpret as the maximum depositional age for this formation. This age is some 15 million years younger than the 541 Ma age reported for the Diamantino Formation by (Bandeira et al., 2011) indicating that deposition in the foreland of the Paraguay orogen continued well into the Cambrian.
Figure 3. Relative probability plots for U-Pb detrital zircon analyses. Light grey shading represents all detrital grains analysed, dark grey represents detrital grains between 90 and 110% concordant. Black line represents the Cambrian/Ediacaran boundary.
in supplemental Table 2. Hf data was collected for each of the eight samples that were analysed for U-Pb isotopes in order to determine the provenance of the protoliths for the Alto Paraguay Group sediments. The analyses are plotted in their respective
72
Chapter 5 Age and provenance of the northern Paraguay Belt
U-Pb and Hafnium isotopic results and correlation with potential source regions
Integrated U-Pb and Hf isotope composition data of detrital zircons from the sedimentary rocks of the northern Paraguay Belt provides insight into the tectonomagmatic evolution of their source areas. The age spectra represented by the samples are characterised by polymodal zircon age spectra
(Figure 3). Suitable source regions would need to contain the same zircon populations to be considered viable. The series of ages can be considered as a diagnostic pattern for the source of the strata in the northern Paraguay Belt. Coupling this with the εHf(t) values, which provide the petrological signature of the melt in which the zircons crystallised it is possible to gain some insight about the source regions for these rocks.
The data presented in the εHf versus time plot in Figure 5 begin with a more evolved signal in the late-Palaeoproterozoic, which gradually becomes more juvenile through most of the Mesoproterozoic. This trend is consistent with the the global data set (Belousova et al., 2010) and also matches the signal for modern day εHf from detrital zircons from the Amazon River represented by the grey envelope (Figure 5). Since
Figure 4 - Zircon morphology. Author: Ben McGee, Extension: .pdf
BDM-01 100 μm
Spot 156527 ± 6 Ma90 % conc.
Spot 188547 ± 8 Ma112 % conc.
Spot 1431265 ± 37 Ma105 % conc.
Spot 188554 ± 10 Ma100 % conc.
Spot 581905 ± 19 Ma96 % conc.
BPUG-02 100 μm
Spot 1071764 ± 22 Ma98 % conc. Spot 49
1737 ± 20 Ma95 % conc.
Spot 621032 ± 27 Ma98 % conc.
Spot 821270 ± 29 Ma92 % conc.
BRZ-02 100 μm
Spot 2936 ± 11 Ma98 % conc.
Spot 18924 ± 11 Ma96 % conc.
Spot 171352 ± 24 Ma100 % conc.
Spot 141048 ± 25 Ma100 % conc.
BRZ-01 100 μm
Spot 19929 ± 12 Ma99 % conc.
Spot 24903 ± 11 Ma97 % conc.
Spot 1091391 ± 23 Ma101 % conc.
Spot 71635 ± 9 Ma93 % conc.
TA01
100 μm
Spot 4988 ± 11 Ma97 % conc.
Spot 171338 ± 24 Ma97 % conc.
Spot 93665 ± 9 Ma92 % conc.
Spot 35665 ± 9 Ma92 % conc.
BST-24100 μm
Spot 151555 ± 20 Ma100 % conc.
Spot 22615 ± 64 Ma99 % conc.
BSA-20
Spot 28934 ± 12 Ma99 % conc.
Spot 34737 ± 9 Ma105 % conc.
BRZ-15100 μm
Spot 81561 ± 28 Ma100 % conc.
Spot 381184 ± 32 Ma99 % conc.
Spot 1201308 ± 27 Ma96 % conc.
Spot 1391203 ± 26 Ma103 % conc.
Spot 60a651 ± 9 Ma93 % conc.
Spot 60b647 ± 9 Ma100 % conc.
Spot 641051 ± 37 Ma99 % conc.
Spot 107b1048 ± 26 Ma102 % conc.
Spot 107a1072 ± 42 Ma102 % conc.
Spot 1551072 ± 42 Ma
102 % conc.
(f )
(c)
BSA-07 100 μm
(b)
(g)
(d)
(e)
(a)
(h)
Figure 4. Cathodoluminescence images of representative zircon grains from sample (a) BDM-01; (b) BST-24; (c) BRZ-15; (d) BRZ-01; (e) BRZ-02; (f) BSA-07; (g) BSA-20 and (h) BPUG-02. Displayed spot ages <1000 Ma and >1000 Ma are 206Pb/238U and 207Pb/206Pb ages respectively. Small circles (30 μm) and large circles (50 μm) represent the location of U-Pb and Lu-Hf analyses respectively.
73
Chapter 5 Age and provenance of the northern Paraguay Belt
the Paraguay Belt is considered to be a sequence of folded sediments that formed on a passive margin on the south-eastern margin of the Amazonian Craton, this is a logical source area for these sediments. This craton comprises two small Archean cores—the Central Amazonian Province (>2600 Ma)—surrounded by predominantly accretionary Paleoproterozoic belts; the Maroni-Itacaiunas Province (2250–2050 Ma); the Ventuari-Tapajós Province (1980–1810 Ma); the Rio Negro-Juruena Province (1780–1550 Ma); the Rondonian-San Ignácio Province (1550–1300 Ma) and the ca. 1250–950 Ma Sunsás Province (Cordani and Teixeira, 2007; Cordani et al., 2009; Tassinari et al., 2000). The similarities in age and the εH signature with modern day Amazon River detrital zircons indicate that the Amazon Craton was a major contributor to the Paraguay Belt sediments. However, the vertical line in Figure 5 represents the minimum age of currently known sources on the Amazonian Craton (950 Ma). If this is taken as the minimum age limit for rocks on this craton, alternative regions must be considered as sources.
Another potential source region to consider are the blocks underneath the Paraná Basin. While
some authors have suggested the existence of several blocks under the Paraná Basin (e.g. Cordani et al., 2003; Milani, 1997), a recent review by Mantovani and Brito Neves (2009) suggested that a simpler interpretation—the existence of one body, the Paranapanema Block—was more favourable. Based on deep oil exploration wells that intersected basement, the Paranapanema Block is described by Mantovani and Brito Neves (2009) as “pre-Brasiliano in general”. This block is likely to have contributed sediment to the Paraguay Belt but due to it’s burial beneath the Paraná Basin it is difficult to assess to what degree.
Bandeira et al. (2011) used palaeocurrent indicators from the upper Diamantino Formation to show that the prevailing source regions are to the east of the present day Paraguay Belt. Potential source regions they identified include the 790–600 Ma Brasilia Belt and the Neoproterozoic Goiás Massif. In Figure 5 we have represented Hf data after Matteini et al. (2010) from the Goiás Massif as closed polygons. These polygons show that the Goiás contains highly juvenile material, but also more evolved material that could have been a potential source for the Paraguay Belt sediments. Bandeira
et al. (2011) interpreted the rest of the sediments to be cannibalised from the rising topography of the Paraguay Belt. The proven presence of zircons with a similar age from within the core of the Paraguay Belt (today to the southeast of the sample site), strongly suggests that the Diamantino Formation was sourced from elevated topography developed during Paraguay Belt orogenesis. This interpretation is supported by the Sm/Nd data of Dantas et al. (2009).
Tectonic model and the Paraguay Belt within South America and Gondwana
Owing to the scarcity of reliable Neoproterozoic palaeomagnetic poles, the location of the Amazonian Craton and its role in Gondwana amalgamation has been the subject of debate for some time (e.g. Cordani et al., 2009; Pisarevsky et al., 2008). The Paraguay Belt on the southern margin of the Amazonian Craton is at the centre of this debate. Currently there are two competing models for the tectonic evolution of the Paraguay Belt and surrounding orogens. The first model considers the ages of juvenile arcs (940–620 Ma) at the western border of the São Francisco
ɛ H
f
Age (Ma)
DM
CHUR
Raizama Formation Serra Azul Formation Diamatino Formation Puga Formation
0 500 1000 1500 2000 2500 3000 3500 -20
-15
-10
-5
0
5
10
15
20
Figure 5 - Epsilon Hf. Author: Ben McGee, Extension: .pdf
Known Amazon Craton Sources
Figure 5. εHf values plotted against…Grains with more than 10% discordancy have been omitted. The grey envelope represents the first to third quartile of modern day zircons collected from the Amazon River (Iizuka et al., 2010). White polygons represent εHf data from the Goiás Massif after Matteini et al. (2010).
74
Chapter 5 Age and provenance of the northern Paraguay Belt
(a) Incipient stages of basin inversion
Peripheral bulge(Proto-Paraguay Belt)
Raizama deposition
Proto-foredeepbasin
Brasiliano ArcAccretionary wedge
Amazon CratonAmazon Craton Paranapanema/Goias Massif
(b) Deepening of the foreland basin
ParaguayOrogen
ForedeepBasin
Amazon CratonAmazon Craton
Paranapanema/Goias Massif
SepotubaFormationDeposition
Brasiliano Arc
(c) Final stages of orogenesis and sediment deposition in Alto Paraguay Group
ParaguayOrogen
Diamantino deposition
Juvenilesediment
input
Amazon CratonAmazon Craton
Paranapanema/Goias Massif
Diamantino Lake
Detachment of oceanic crust
Figure 6 - Tectonic Model. Author: Ben McGee, Extension: .pdf
Figure 6. Tectonic model for the evolution of the Paraguay Belt. (a) Initiation of compression resulting in flexural warping of the litho-sphere and deposition of the Raizama Formation into the proto-foredeep basin; (b) Continued lithospheric flexure and deepening of the foredeep basin; (c) Termination of orogenesis and deposition of the Diamantino Formation into the Diamantino Lake.
Craton to represent the age of collision of the Amazonian Craton with proto-Gondwana, implying suturing at ~620 Ma (Cordani et al., 2009). In this scenario the Paraguay Belt sediments would presumably represent a rift basin that was subsequently inverted. However, little evidence for ca. 620 Ma orogenesis exists, with ages of metamorphism and intrusive plutons much younger in age.
The second model, proposed by Trindade et al. (2006), used a palaeomagnetic pole (Trindade
et al. 2003) that suggested that the Amazonian Craton was at low latitudes and not joined to Gondwana until Cambrian times. The hypothesis infers that the Amazonian Craton and other minor adjoining blocks were separated from proto-Gondwana by the Clymene Ocean and collided in the Cambrian forming a major orogenic belt, comprising the Araguaia, Paraguay and Pampean belts. Several other contributions have since provided evidence that corroborate such an evolution for
the Paraguay Belt based on a range of different evidence.
Sedimentation and provenance studies have helped to constrain the depositional environments and sources for the Paraguay Belt sediments. Geochemical provenance patterns of the northern Paraguay Belt were investigated by Dantas et al. (2009), where they studied the Nd isotopic signature of rocks in the sequence. They found that the lower part of the succession was dominated by Nd isotopic ratios that and TDM model ages that
75
Chapter 5 Age and provenance of the northern Paraguay Belt
suggest a continental source from the Amazonian Craton, whilst the upper siliciclastic succession shows lower Nd isotopic ratios that is consistent with a source from the Paraguay Belt itself, or another Neoproterozoic continental source. More recently, detrital zircon ages from the Diamantino Formation of 541 Ma (Bandeira et al., 2011) and 40Ar/39Ar muscovite ages from the upper part of the Alto Paraguay Group of 544 Ma (McGee et al. submitted) indicate that final sedimentation within the Paraguay Belt occurred up to the Cambrian. The U-Pb data presented here add to this database of maximum depositional ages for the sediments of the Paraguay Belt.
Several authors have also investigated the timing of deformation and metamorphism within the orogen. Regional metamorphism of the Cuiabá Group was estimated between 541 and 531 Ma based on 40Ar/39Ar cooling ages of biotite flakes (Geraldes et al., 2008). The incipient stages of deformation in the form of early thrusting was inferred to be associated with clay mineral transformations and chemical remagnetisation of carbonates in the Araras Group at ca. 528 Ma (Tohver et al., 2010). In this contribution Tohver et al. (2010) showed that oroclinal bending of the Paraguay Belt was caused by a 90° clockwise rotation of the east-limb some time after 528 Ma. Tohver et al. (2010) also pointed out that the age of the Paraguay Belt overlaps with that of the Pampean Belt further south suggesting that a coeval closure for the Clymene Ocean separating the Amazonian Craton from the São Francisco and Rio de la Plata cratons. Tohver et al. (2011) elaborated on the theory of a Cambrian formation for Gondwana with evidence from the Sierra Australis, including late Ediacaran to late Cambrian magmatism and showing a close overlap of geochronological data with Clymene collision belts to the north—the Paraguay and Araguaia belts.
A geophysical study that combined magnetotelluric and
gravimetric data proposed that a plate interaction zone exists at the western border of the Paraná Basin, proposing a collision between the Rio Apa Craton to the west and the Paranapanema Block to the east (Woldemichael, 2003). Woldemichael (2003) modeled this interaction as a subduction zone from 550–520 Ma of the Rio Apa oceanic crust under the Paranapanema with the development of an Andean type magmatic arc. A subsequent investigation of the geochemistry of the granitic bodies that outcrop at the western margin of the Paraná Basin showed that these rocks are potassic to high K, calc-alkaline, peraluminous to metaluminous, type-I granitoids that plot in the syn-collisional field of the tectonic classification diagrams (Godoy et al., 2007). Early work constraining the ages of these intrusives include a 503 Ma K/Ar age (Almeida, 1968) and 483 Ma Rb/Sr age (Almeida and Mantovani, 1975) for the post-orogenic São Vicente granite (Figure 1). These ages have been supported by more recent U-Pb zircon analyses of the same intrusive batholith of 521 Ma (Ferreira, 2009) and 518 Ma (McGee et al., 2012). Other granitic intrusions from the interior of the belt have similar ages including a U-Pb SHRIMP zircon age of 510 ± 12 Ma for the Araguainha Granite (Tohver et al., 2012) and the Lajinha Granite which yielded a U-Pb zircon age of 505.4 ± 4.1 Ma (Manzano, 2009).
The palaeomagnetic result of Trindade et al. (2003) that suggested the Amazon was not connected to proto-Gondwana until the Cambrian has recently been questioned, after McGee et al. (Submitted) reproduced similar geomagnetic reversals of an orientation very similar to those of Trindade et al (2003) much higher in the stratigraphy, from the Alto Paraguay Group. McGee et al. (Submitted) suggested that this result is indicative of a remagnetisation, potentially associated with Jurassic tholeittic basalts that intrude into the western part of the northern Paraguay Belt. If this is the case, the palaeomagnetic database no longer
provides information about the location of the Amazonian Craton for much of the Neoproterozoic, leaving the tectonic evolution of the belt open to debate. Despite this uncertainty in the palaeomagnetic database, the amount of other supporting evidence for a late (Cambrian) collision of Amazonia is difficult to ignore.
Based on this amalgam of evidence and our new U-Pb and Hf data we propose a tectonic model (Figure 6) that incorporates all of this information. The first sediments found on the Amazonian Craton are the glacial diamictites of the Puga Formation and the more distal turbidites of the Cuiaba Group. The thickness (4–6 km) and aerial extent (~700 km) of these units is suggestive of a large marine basin, which has previously been proposed by numerous authors (e.g. Alvarenga and Trompette, 1992; Alvarenga et al., 2009; Nogueira et al., 2007). The depositional model proposed for these units is in a passive margin environment from platformal to outer slope from west to east respectively (Alvarenga and Trompette, 1992). This period of deposition was followed by a period of glaciation responsible for depositing the Serra Azul Formation in a glaciomarine environment inferred to be related to the Gaskiers glaciation (Alvarenga et al., 2007; McGee et al., Under Review).
The conformable nature of the Raizama Formation with the upper Serra Azul Formation implies the gradual initiation of topography and that the deposition of the Raizama Formation was tectonically controlled by this rising topography. We propose that the incipient stages of deformation—the ‘proto-Paraguay Orogeny’—formed as a peripheral bulge (Figure 6a) in response to the flexural warping of the lithosphere. This lithospheric deformation and associated basin inversion begun as oceanic crust connected to the Amazonian Craton was thrust under the Paranapanema Block and the Goiás Massif. In such a system a downwarp is generated proximal to the orogen, the foreland
76
Chapter 5 Age and provenance of the northern Paraguay Belt
basin, and a low amplitude, long-wavelength upwarp, the peripheral bulge developes proximal to subduction (Catuneanu et al., 1997). A minor influence from volcanic arcs is interpreted in the Raizama Formation based on the U-Pb ages reported in this study. These arcs are probably now buried under the Paraná Basin, to the south east of the Paraguay Belt (Figure 1), and their presence and morphology has been interpreted based on petroleum wells and geophysical techniques (Mantovani and Brito Neves, 2009). Based on currently available ages the Raizama Formation was deposited after middle Ediacaran times (~582 Ma). The Raizama Formation also does not contain the prominent ~544 Ma detritus seen in the overlying Diamantino Formation suggesting that it probably predates this time.
After deposition of the Raizama Formation, a major decrease in sand content and the predominance of siltstone (McGee et al., Submitted) indicates deepening of the foreland basin (Figure 6b). This most likely occurred in response to increased lithospheric flexure as the collision advanced on the Amazonian margin. At this time the interlayered sandstones and siltstones of the Sepotuba Formation were deposited into the foreland basin.
The stacking of progradational parasequences indicates that the basin was progressively filled with coarser sediment of the Diamantino Formation (Figure 6c). Bandeira et al. (2011) interpreted the Diamantino Formation to record the final exhumation and erosion of the orogen that was deposited into the foreland basin—which they interpreted to be a closed system by this stage—the ‘Diamantino Lake’. Another indicator that the Diamantino Formation is likely to be lacustrine is that the majority of correlative marine Cambrian sequences contain fossils (Aceñolaza et al., 2009), whilst none have been reported for the Diamantino Formation. The predominance of much younger muscovite ages in the Diamantino Formation most likely represents
the increased input from the upper plate of the colliding blocks (the Paranapanema block and Goiás Massif; Figure 7d) and, as previously discussed, the cannibalisation of igneous plutons from within the belt and metamorphic ages as the rocks were exhumed and cooled through the muscovite closure temperature. These ages for final sedimentation and exhumation at circa 544 Ma are in agreement with the observed intrusion of post-orogenic granites at 518 Ma (McGee et al., 2012) and indicate that detachment of the down-going oceanic slab and subsequent removal of the slab-pull force, resulting in the cessation of compressional tectonics, occurred around this time (Figure d). All these data are consistent with an ocean to the east of the Amazonian Craton that didn’t close until the Cambrian.
CONCLUSIONS
The maximum depositional ages provided by the U-Pb zircon analyses from the uppermost part of this sequence of rocks, the Diamantino Formation, indicate final sedimentation in the Paraguay Belt began no earlier than 527 Ma. Based on the integrated U-Pb and Hf isotope data of detrital zircons presented here, potential sources for these sediments are consistent with a predominantly Amazonian source until the early-Neoproterozoic at which point the signal becomes significantly more evolved and influence from the Paranapanema, and Goiás Massif to the east are inferred. Based on the combination of magnetotelluric, gravimetric, geochemical, geochronological and sedimentological evidence discussed here we propose that the Paraguay Belt inititated as a peripheral bulge in response to subduction of Amazonian oceanic crust underneath the Paranapanema Block. Available evidence suggests that final sedimentation, deformation and metamorphism in the Paraguay Belt occurred between 540 and 510 Ma.
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Chapter 5 Age and provenance of the northern Paraguay Belt
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79
Chapter 5 Age and provenance of the northern Paraguay Belt
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80
Chapter 5 Age and provenance of the northern Paraguay BeltTa
ble
1. L
A-IC
PM
S Z
ircon
U-T
h-P
b A
ge D
ata
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 10.
320.
0721
0.00
130.
1559
0.00
211.
5481
0.02
970.
0479
0.00
110.
699
988
3793
412
950
1294
521
9593
4
Spo
t 20.
260.
0799
0.00
100.
2019
0.00
282.
2249
0.03
390.
0601
0.00
090.
910
1196
2511
8515
1189
1111
8118
9911
96
Spo
t 30.
330.
0751
0.00
130.
1768
0.00
241.
8300
0.03
350.
0574
0.00
120.
726
1071
3510
4913
1056
1211
2823
9810
71
Spo
t 40.
360.
0731
0.00
100.
1658
0.00
221.
6700
0.02
600.
0497
0.00
080.
833
1017
2898
912
997
1098
016
9798
9
Spo
t 51.
670.
0794
0.00
270.
1509
0.00
231.
6515
0.05
570.
0474
0.00
090.
460
1182
6690
613
990
2193
517
7790
6
Spo
t 61.
020.
1082
0.00
170.
3084
0.00
414.
6005
0.07
600.
0890
0.00
140.
811
1770
2817
3320
1749
1417
2325
9817
70
Spo
t 70.
730.
1095
0.00
130.
3141
0.00
404.
7419
0.06
430.
0896
0.00
120.
946
1791
2117
6120
1775
1117
3522
9817
91
Spo
t 80.
410.
0798
0.00
110.
2015
0.00
292.
2181
0.03
650.
0581
0.00
090.
866
1193
2711
8415
1187
1211
4218
9911
93
Spo
t 90.
360.
0797
0.00
100.
2018
0.00
282.
2170
0.03
410.
0579
0.00
090.
897
1190
2511
8515
1186
1111
3817
100
1190
Spo
t 10
1.33
0.10
820.
0015
0.30
890.
0041
4.60
540.
0702
0.08
720.
0012
0.86
317
6825
1735
2017
5013
1690
2298
1768
Spo
t 12
0.82
0.09
260.
0014
0.25
830.
0034
3.29
680.
0528
0.07
570.
0011
0.82
714
7928
1481
1814
8012
1475
2110
014
79
Spo
t 13
0.31
0.07
160.
0012
0.15
510.
0021
1.53
210.
0280
0.04
620.
0010
0.73
097
635
930
1294
311
914
1995
930
Spo
t 14
0.42
0.09
770.
0014
0.28
460.
0040
3.83
560.
0610
0.08
000.
0015
0.87
315
8126
1615
2016
0013
1556
2810
215
81
Spo
t 16
1.31
0.11
390.
0012
0.31
970.
0044
5.02
120.
0686
0.08
620.
0009
0.99
918
6319
1788
2118
2312
1671
1796
1863
Spo
t 17
0.28
0.08
600.
0011
0.22
200.
0029
2.63
310.
0383
0.06
430.
0011
0.89
213
3925
1293
1513
1011
1260
2197
1339
Spo
t 18
0.24
0.07
370.
0014
0.16
270.
0022
1.65
240.
0320
0.04
820.
0013
0.70
110
3237
972
1299
112
952
2594
1032
Spo
t 19
2.54
0.07
840.
0036
0.15
090.
0026
1.63
020.
0727
0.04
560.
0009
0.39
111
5787
906
1598
228
902
1878
906
Spo
t 20
0.51
0.08
670.
0013
0.22
820.
0030
2.72
690.
0434
0.06
660.
0012
0.83
413
5328
1325
1613
3612
1304
2298
1353
Spo
t 21
0.32
0.07
870.
0017
0.20
130.
0031
2.18
350.
0479
0.05
380.
0018
0.70
211
6341
1182
1711
7615
1059
3510
211
63
Spo
t 22
0.45
0.13
400.
0016
0.34
720.
0054
6.41
310.
1008
0.05
420.
0009
0.98
421
5120
1921
2620
3414
1067
1789
2151
Spo
t 23
3.44
0.07
390.
0018
0.15
560.
0023
1.58
520.
0404
0.04
320.
0006
0.58
010
3849
932
1396
416
855
1190
932
Spo
t 24
0.87
0.09
270.
0012
0.25
710.
0036
3.28
680.
0500
0.06
770.
0009
0.91
214
8224
1475
1814
7812
1324
1699
1482
Spo
t 25
0.37
0.07
120.
0015
0.15
860.
0022
1.55
780.
0330
0.05
110.
0012
0.65
496
441
949
1295
413
1008
2498
949
Spo
t 26
0.39
0.09
440.
0011
0.27
850.
0036
3.62
530.
0503
0.07
990.
0013
0.93
315
1622
1584
1815
5511
1554
2410
415
16
Spo
t 28
0.34
0.08
230.
0009
0.21
180.
0029
2.40
180.
0342
0.05
900.
0008
0.96
712
5222
1238
1612
4310
1158
1499
1252
Spo
t 29
1.66
0.07
190.
0020
0.15
720.
0023
1.55
830.
0442
0.04
820.
0009
0.52
198
356
941
1395
418
951
1696
941
Spo
t 30
0.28
0.07
010.
0010
0.16
060.
0021
1.55
240.
0247
0.04
840.
0009
0.83
093
229
960
1295
110
955
1810
396
0
Spo
t 31
0.31
0.08
620.
0011
0.23
280.
0032
2.76
750.
0412
0.07
400.
0014
0.91
313
4324
1349
1713
4711
1443
2610
013
43
Spo
t 32
0.21
0.07
300.
0011
0.16
490.
0022
1.65
940.
0282
0.05
670.
0013
0.78
810
1431
984
1299
311
1114
2597
984
Spo
t 33
0.60
0.08
440.
0027
0.21
460.
0034
2.49
860.
0782
0.06
290.
0019
0.50
013
0360
1253
1812
7223
1233
3696
1303
Spo
t 34
0.50
0.07
370.
0013
0.17
050.
0024
1.73
230.
0335
0.05
220.
0010
0.72
810
3336
1015
1310
2112
1029
1898
1033
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
Sam
ple
BS
A-2
0
81
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 35
0.30
0.07
590.
0011
0.17
620.
0024
1.84
240.
0305
0.05
420.
0011
0.80
710
9130
1046
1310
6111
1066
2196
1091
Spo
t 36
0.42
0.07
580.
0018
0.15
700.
0024
1.63
990.
0400
0.04
900.
0012
0.61
910
8946
940
1398
615
966
2486
940
Spo
t 37
0.73
0.06
500.
0014
0.11
800.
0017
1.05
810.
0234
0.03
730.
0008
0.64
877
544
719
1073
312
739
1593
719
Spo
t 38
1.18
0.10
770.
0015
0.31
930.
0043
4.74
100.
0739
0.09
110.
0015
0.86
217
6125
1786
2117
7513
1762
2810
117
61
Spo
t 39
0.39
0.08
800.
0017
0.19
260.
0028
2.33
620.
0468
0.05
030.
0014
0.71
213
8236
1136
1512
2314
991
2682
1382
Spo
t 40
0.50
0.07
520.
0015
0.17
080.
0024
1.77
080.
0365
0.05
030.
0011
0.67
710
7439
1017
1310
3513
992
2295
1074
Spo
t 41
0.57
0.08
700.
0011
0.23
530.
0032
2.82
000.
0416
0.07
030.
0009
0.92
813
5923
1362
1713
6111
1372
1810
013
59
Spo
t 42
0.32
0.08
030.
0014
0.20
580.
0029
2.27
880.
0428
0.06
020.
0016
0.75
412
0534
1206
1612
0613
1182
3010
012
05
Spo
t 44
0.67
0.12
470.
0014
0.32
080.
0046
5.51
870.
0811
0.09
230.
0031
0.97
420
2520
1794
2219
0413
1785
5889
2025
Spo
t 45
0.50
0.07
360.
0010
0.15
990.
0021
1.62
170.
0249
0.04
720.
0008
0.86
410
2927
956
1297
910
933
1693
956
Spo
t 46
0.48
0.08
690.
0013
0.21
110.
0028
2.52
970.
0417
0.05
910.
0012
0.80
713
5829
1235
1512
8112
1160
2391
1358
Spo
t 47
0.30
0.07
160.
0021
0.16
240.
0024
1.60
380.
0473
0.05
110.
0018
0.49
997
559
970
1397
218
1007
3599
970
Spo
t 49
0.26
0.07
400.
0013
0.15
950.
0022
1.62
640.
0303
0.04
600.
0012
0.73
810
4135
954
1298
112
908
2392
954
Spo
t 50
0.34
0.08
450.
0016
0.20
140.
0028
2.34
680.
0464
0.05
950.
0015
0.71
113
0536
1183
1512
2714
1169
2991
1305
Spo
t 53
0.48
0.09
770.
0012
0.27
240.
0039
3.66
740.
0565
0.07
960.
0011
0.93
715
8023
1553
2015
6412
1549
2198
1580
Spo
t 54
0.32
0.07
240.
0013
0.16
520.
0023
1.64
860.
0311
0.04
910.
0012
0.72
899
836
985
1398
912
969
2399
985
Spo
t 55
0.57
0.08
960.
0022
0.20
040.
0031
2.47
430.
0610
0.05
900.
0018
0.62
914
1745
1177
1712
6518
1159
3483
1417
Spo
t 56
0.29
0.07
620.
0011
0.17
640.
0025
1.85
310.
0313
0.05
380.
0010
0.82
111
0030
1048
1310
6511
1058
2095
1100
Spo
t 57
0.40
0.07
920.
0022
0.17
840.
0028
1.94
690.
0537
0.06
050.
0025
0.56
311
7754
1058
1510
9719
1186
4890
1177
Spo
t 58
0.40
0.12
470.
0014
0.35
620.
0049
6.12
510.
0859
0.10
400.
0026
0.97
320
2520
1964
2319
9412
2000
4797
2025
Spo
t 60
0.38
0.07
320.
0008
0.17
430.
0023
1.75
960.
0239
0.05
220.
0010
0.95
810
2022
1036
1210
319
1029
1910
210
20
Spo
t 64
0.55
0.08
400.
0016
0.23
100.
0032
2.67
330.
0523
0.06
900.
0017
0.71
812
9136
1340
1713
2114
1349
3110
412
91
Spo
t 66
0.32
0.07
730.
0021
0.15
640.
0025
1.66
690.
0465
0.05
280.
0025
0.58
21 1
2954
937
1499
618
1039
4783
937
Spo
t 68
0.29
0.08
360.
0019
0.21
580.
0031
2.48
770.
0579
0.06
850.
0024
0.62
612
8344
1260
1712
6917
1339
4598
1283
Spo
t 70
0.34
0.08
060.
0013
0.19
170.
0026
2.13
040.
0369
0.05
640.
0014
0.78
612
1231
1130
1411
5912
1109
2693
1212
Spo
t 72
0.51
0.07
450.
0015
0.17
150.
0024
1.76
140.
0360
0.05
090.
0012
0.68
510
5539
1020
1310
3113
1004
2497
1055
Spo
t 73
0.28
0.07
230.
0019
0.15
680.
0024
1.56
310.
0421
0.04
470.
0017
0.56
199
453
939
1395
617
884
3494
939
Spo
t 74
0.27
0.07
840.
0011
0.19
820.
0029
2.14
150.
0368
0.05
360.
0010
0.86
011
5729
1166
1611
6212
1056
2010
111
57
Spo
t 76
0.57
0.06
930.
0028
0.10
660.
0018
1.01
820.
0401
0.02
960.
0011
0.42
490
780
653
1071
320
590
2272
653
Spo
t 76r
10.
590.
0693
0.00
860.
1086
0.00
321.
0371
0.12
560.
0344
0.00
300.
246
907
236
665
1972
363
683
5873
665
Spo
t 76r
21.
170.
2114
0.00
950.
0842
0.00
222.
4548
0.09
900.
0351
0.00
180.
639
2916
7152
113
1259
2969
834
1852
1
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
82
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 77
0.63
0.11
050.
0018
0.32
260.
0047
4.91
600.
0866
0.08
630.
0028
0.82
218
0829
1802
2318
0515
1673
5110
018
08
Spo
t 78
0.26
0.08
000.
0010
0.20
340.
0027
2.24
190.
0328
0.05
550.
0013
0.90
311
9624
1193
1411
9410
1092
2510
011
96
Spo
t 79
0.32
0.08
310.
0020
0.20
270.
0032
2.32
380.
0576
0.05
670.
0028
0.63
712
7246
1190
1712
2018
1115
5494
1272
Spo
t 84
0.27
0.07
960.
0012
0.20
110.
0027
2.20
740.
0360
0.05
800.
0015
0.83
011
8728
1181
1511
8311
1140
2999
1187
Spo
t 85
0.33
0.08
180.
0013
0.19
930.
0027
2.24
680.
0388
0.05
790.
0015
0.79
412
4131
1171
1511
9612
1137
2994
1241
Spo
t 88
0.24
0.08
300.
0011
0.21
690.
0031
2.48
110.
0389
0.05
750.
0027
0.90
912
6925
1265
1612
6711
1130
5110
012
69
Spo
t 89
0.54
0.08
310.
0017
0.20
530.
0030
2.35
190.
0509
0.06
010.
0016
0.66
412
7140
1204
1612
2815
1179
3195
1271
Spo
t 90
0.27
0.07
040.
0012
0.15
980.
0022
1.55
070.
0291
0.04
520.
0013
0.73
893
935
956
1295
112
893
2510
295
6
Spo
t 91
0.30
0.08
750.
0010
0.21
390.
0028
2.57
930.
0367
0.06
510.
0015
0.93
313
7123
1250
1512
9510
1275
2891
1371
Spo
t 93
0.41
0.06
350.
0017
0.10
870.
0016
0.95
120.
0263
0.03
190.
0010
0.53
272
457
665
967
914
635
2092
665
Spo
t 95
0.27
0.08
760.
0011
0.24
720.
0033
2.98
430.
0426
0.06
970.
0016
0.93
213
7423
1424
1714
0411
1361
3110
413
74
Spo
t 101
0.31
0.07
850.
0040
0.16
080.
0031
1.74
090.
0877
0.05
200.
0035
0.38
811
6099
961
1710
2432
1024
6783
961
Spo
t 103
0.37
0.08
040.
0012
0.23
880.
0034
2.64
680.
0453
0.06
830.
0023
0.82
512
0730
1381
1813
1413
1335
4311
412
07
Spo
t 107
0.10
0.07
130.
0010
0.15
830.
0023
1.55
590.
0260
0.04
570.
0022
0.85
396
629
947
1395
310
904
4398
947
Spo
t 108
0.35
0.09
910.
0016
0.29
050.
0042
3.96
810.
0721
0.08
820.
0033
0.80
316
0730
1644
2116
2815
1708
6210
216
07
Spo
t 110
0.44
0.09
800.
0014
0.28
250.
0039
3.81
650.
0598
0.08
060.
0022
0.87
315
8725
1604
1915
9613
1567
4110
115
87
Spo
t 111
0.71
0.11
000.
0014
0.32
520.
0047
4.92
990.
0776
0.08
770.
0049
0.92
017
9923
1815
2318
0713
1699
9110
117
99
Spo
t 112
0.23
0.06
980.
0009
0.15
940.
0021
1.53
260.
0224
0.04
730.
0013
0.91
492
125
953
1294
49
934
2410
395
3
Spo
t 114
0.39
0.09
480.
0011
0.26
260.
0035
3.43
060.
0489
0.07
290.
0019
0.93
815
2422
1503
1815
1111
1422
3699
1524
Spo
t 117
0.29
0.07
160.
0010
0.15
690.
0021
1.54
860.
0254
0.04
630.
0013
0.82
997
529
939
1295
010
915
2696
939
Spo
t 118
0.24
0.17
520.
0018
0.10
730.
0014
2.59
140.
0338
0.13
200.
0033
0.99
926
0817
657
812
9810
2506
5825
657
Spo
t 120
0.24
0.07
120.
0019
0.15
390.
0023
1.51
080.
0414
0.04
680.
0021
0.54
396
354
923
1393
517
925
4096
923
Spo
t 121
0.29
0.08
430.
0012
0.21
380.
0030
2.48
610.
0407
0.06
090.
0020
0.84
813
0028
1249
1612
6812
1195
3896
1300
Spo
t 125
0.30
0.07
940.
0021
0.19
270.
0030
2.10
950.
0575
0.06
190.
0027
0.56
911
8352
1136
1611
5219
1214
5196
1183
Spo
t 127
0.26
0.10
170.
0019
0.28
120.
0044
3.93
900.
0790
0.06
780.
0064
0.77
316
5534
1598
2216
2216
1326
121
9716
55
Spo
t 130
0.82
0.11
110.
0014
0.32
570.
0046
4.98
960.
0751
0.08
110.
0040
0.93
718
1822
1818
2218
1813
1577
7510
018
18
Spo
t 131
0.29
0.07
100.
0014
0.15
890.
0022
1.55
530.
0313
0.04
270.
0015
0.70
095
838
950
1295
312
845
2999
950
Spo
t 132
0.38
0.07
100.
0024
0.16
680.
0028
1.63
310.
0557
0.04
980.
0026
0.48
995
868
995
1598
321
981
5010
499
5
Spo
t 139
0.32
0.07
450.
0011
0.18
140.
0025
1.86
160.
0311
0.05
350.
0017
0.81
510
5430
1074
1310
6811
1054
3210
210
54
Spo
t 141
1.83
0.07
880.
0024
0.16
500.
0026
1.79
350.
0541
0.04
760.
0014
0.51
611
6859
985
1410
4320
940
2784
985
Spo
t 145
0.35
0.09
680.
0013
0.27
200.
0037
3.63
000.
0544
0.07
540.
0022
0.89
815
6424
1551
1915
5612
1469
4099
1564
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
83
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 147
0.32
0.09
670.
0012
0.29
010.
0039
3.86
600.
0562
0.08
100.
0023
0.91
815
6123
1642
1916
0712
1574
4310
515
61
Spo
t 148
0.29
0.07
630.
0019
0.17
400.
0026
1.83
020.
0454
0.05
110.
0022
0.61
211
0348
1034
1410
5616
1007
4394
1103
Spo
t 149
0.32
0.08
450.
0011
0.23
800.
0032
2.77
350.
0410
0.06
590.
0019
0.90
413
0424
1376
1713
4811
1289
3510
613
04
Spo
t 151
0.53
0.08
180.
0021
0.21
220.
0034
2.39
030.
0634
0.05
840.
0032
0.60
412
4050
1240
1812
4019
1148
6110
012
40
Spo
t 154
0.39
0.07
080.
0012
0.15
800.
0022
1.54
210.
0285
0.04
400.
0014
0.74
695
135
946
1294
711
871
2699
946
Spo
t 20.
350.
1160
0.00
120.
3112
0.00
414.
9768
0.06
570.
0902
0.00
110.
986
1896
1917
4720
1815
1117
4621
9218
96
Spo
t 30.
330.
0984
0.00
170.
2693
0.00
433.
6537
0.07
180.
0905
0.00
250.
803
1594
3215
3722
1561
1617
5146
9615
94
Spo
t 70.
630.
0917
0.00
140.
2443
0.00
343.
0888
0.05
250.
0701
0.00
110.
821
1462
2914
0918
1430
1313
6921
9614
62
Spo
t 80.
130.
0763
0.00
110.
1703
0.00
231.
7914
0.02
930.
0578
0.00
150.
832
1103
2910
1413
1042
1111
3628
9211
03
Spo
t 12
0.76
0.09
940.
0026
0.25
940.
0049
3.55
530.
0958
0.08
250.
0024
0.70
116
1347
1487
2515
4021
1603
4692
1613
Spo
t 13
0.54
0.07
920.
0019
0.17
050.
0030
1.86
200.
0480
0.05
520.
0016
0.67
511
7848
1015
1610
6817
1087
3186
1178
Spo
t 14
0.33
0.07
470.
0011
0.16
430.
0023
1.69
110.
0289
0.04
830.
0009
0.81
710
6030
981
1310
0511
952
1793
981
Spo
t 15
0.61
0.10
890.
0014
0.30
590.
0042
4.59
190.
0699
0.08
440.
0012
0.90
717
8123
1720
2117
4813
1637
2397
1781
Spo
t 19
0.12
0.10
630.
0015
0.24
450.
0037
3.58
320.
0613
0.16
990.
0040
0.88
817
3725
1410
1915
4614
3172
6981
1737
Spo
t 20
0.28
0.08
200.
0016
0.17
770.
0028
2.00
770.
0425
0.06
980.
0019
0.73
612
4637
1054
1511
1814
1364
3585
1246
Spo
t 22
0.35
0.10
280.
0014
0.27
200.
0038
3.85
650.
0601
0.07
830.
0014
0.88
716
7625
1551
1916
0513
1523
2693
1676
Spo
t 23
0.37
0.09
720.
0011
0.27
420.
0039
3.67
280.
0541
0.08
470.
0014
0.95
315
7121
1562
1915
6612
1644
2599
1571
Spo
t 24
0.22
0.12
490.
0016
0.19
940.
0030
3.43
340.
0560
0.12
110.
0023
0.93
420
2722
1172
1615
1213
2310
4158
2027
Spo
t 25
0.70
0.09
690.
0018
0.23
850.
0036
3.18
270.
0637
0.07
630.
0016
0.76
015
6434
1379
1914
5315
1486
2988
1564
Spo
t 26
0.34
0.07
360.
0009
0.17
1 10.
0023
1.73
600.
0250
0.04
890.
0007
0.92
310
3124
1018
1310
229
965
1399
1031
Spo
t 27
0.15
0.08
130.
0015
0.16
960.
0027
1.89
960.
0394
0.07
730.
0024
0.76
712
2836
1010
1510
8114
1506
4582
1228
Spo
t 28
0.38
0.09
660.
0012
0.26
370.
0035
3.51
440.
0504
0.07
510.
0012
0.92
915
6022
1509
1815
3011
1464
2297
1560
Spo
t 31
0.45
0.09
680.
0014
0.25
330.
0035
3.38
230.
0550
0.07
590.
0014
0.84
015
6427
1455
1815
0013
1479
2793
1564
Spo
t 32
0.67
0.07
310.
0010
0.16
310.
0022
1.64
380.
0250
0.04
820.
0006
0.87
910
1726
974
1298
710
952
1296
974
Spo
t 33
0.45
0.11
000.
0015
0.31
490.
0046
4.77
450.
0778
0.08
580.
0017
0.90
417
9924
1765
2317
8014
1664
3198
1799
Spo
t 34
0.34
0.10
010.
0012
0.27
370.
0038
3.77
800.
0553
0.07
120.
0012
0.95
616
2721
1559
1915
8812
1391
2296
1627
Spo
t 35
1.22
0.07
350.
0015
0.16
190.
0023
1.64
000.
0354
0.05
060.
0009
0.65
310
2642
967
1398
614
998
1794
1026
Spo
t 37
0.37
0.07
490.
0008
0.17
400.
0023
1.79
570.
0242
0.05
020.
0006
0.99
010
6521
1034
1310
449
990
1197
1065
Spo
t 40
0.56
0.09
030.
0016
0.24
980.
0035
3.11
070.
0591
0.06
740.
0013
0.74
014
3334
1437
1814
3515
1319
2510
014
33
Spo
t 41
0.30
0.09
660.
0012
0.27
060.
0036
3.60
300.
0516
0.07
970.
0014
0.91
615
5923
1544
1815
5011
1550
2699
1559
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
Sam
ple
BP
UG
-02
84
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 42
0.47
0.07
550.
0014
0.16
930.
0023
1.76
330.
0340
0.05
050.
0011
0.71
710
8236
1008
1310
3212
995
2093
1082
Spo
t 44
0.60
0.09
350.
0013
0.22
780.
0031
2.93
570.
0469
0.06
900.
0012
0.84
014
9827
1323
1613
9112
1349
2288
1498
Spo
t 45
0.65
0.07
580.
0009
0.16
980.
0022
1.77
510.
0254
0.05
120.
0007
0.91
210
9024
1011
1210
369
1009
1493
1090
Spo
t 46
0.66
0.10
480.
0014
0.26
930.
0037
3.89
000.
0611
0.07
580.
0013
0.87
817
1125
1537
1916
1213
1478
2390
1711
Spo
t 47
0.34
0.08
960.
0013
0.23
390.
0032
2.88
880.
0462
0.06
570.
0013
0.85
514
1727
1355
1713
7912
1287
2496
1417
Spo
t 48
0.38
0.09
120.
0012
0.23
440.
0033
2.94
680.
0470
0.06
570.
0011
0.89
314
5025
1358
1713
9412
1286
2094
1450
Spo
t 49
0.53
0.10
640.
0012
0.29
340.
0037
4.30
290.
0569
0.08
050.
0016
0.94
917
3821
1659
1816
9411
1566
3095
1738
Spo
t 50
0.36
0.09
980.
0015
0.24
920.
0035
3.42
740.
0561
0.07
540.
0023
0.84
816
2027
1434
1815
1113
1470
4489
1620
Spo
t 51
0.55
0.08
930.
0013
0.24
190.
0033
2.98
110.
0498
0.07
010.
0013
0.82
114
1128
1397
1714
0313
1369
2499
1411
Spo
t 52
0.30
0.10
060.
0015
0.18
180.
0025
2.52
240.
0421
0.09
010.
0017
0.81
516
3628
1077
1312
7912
1744
3266
1636
Spo
t 53
0.09
0.07
130.
0012
0.16
570.
0021
1.62
820.
0278
0.05
450.
0020
0.74
796
533
988
1298
111
1072
3910
298
8
Spo
t 54
0.23
0.09
690.
0012
0.27
280.
0036
3.64
460.
0526
0.08
300.
0015
0.91
915
6522
1555
1815
5912
1612
2899
1565
Spo
t 55
0.52
0.07
510.
0013
0.16
830.
0023
1.74
250.
0317
0.05
060.
0010
0.75
710
7033
1003
1310
2412
997
1994
1070
Spo
t 56
0.44
0.09
690.
0011
0.26
370.
0033
3.52
420.
0469
0.07
890.
0011
0.93
115
6621
1509
1715
3311
1535
2196
1566
Spo
t 57
0.66
0.09
770.
0016
0.26
970.
0036
3.63
160.
0634
0.08
230.
0015
0.75
415
8031
1539
1815
5714
1599
2997
1580
Spo
t 59
0.29
0.07
390.
0012
0.16
980.
0022
1.72
960.
0298
0.05
080.
0012
0.75
610
3832
1011
1210
2011
1001
2297
1038
Spo
t 62
0.51
0.07
370.
0010
0.16
930.
0024
1.71
940.
0278
0.04
950.
0007
0.85
910
3228
1008
1310
1610
977
1498
1032
Spo
t 63
0.06
0.09
610.
0011
0.26
980.
0035
3.57
430.
0484
0.08
230.
0017
0.95
315
4921
1540
1815
4411
1599
3299
1549
Spo
t 64
0.66
0.10
100.
0016
0.27
160.
0037
3.78
250.
0648
0.08
200.
0016
0.80
216
4329
1549
1915
8914
1593
2994
1643
Spo
t 65
0.22
0.09
370.
001 1
0.22
010.
0027
2.84
200.
0378
0.06
270.
0011
0.90
915
0122
1282
1413
6710
1229
2185
1501
Spo
t 66
0.43
0.09
690.
0021
0.24
330.
0035
3.25
040.
0701
0.07
450.
0021
0.66
915
6639
1404
1814
6917
1452
4090
1566
Spo
t 67
0.36
0.09
660.
0015
0.27
250.
0038
3.62
740.
0610
0.07
920.
0021
0.81
915
5928
1553
1915
5613
1541
3910
015
59
Spo
t 68
0.32
0.08
180.
0021
0.17
120.
0027
1.93
130.
0501
0.06
400.
0025
0.60
112
4150
1019
1510
9217
1255
4882
1241
Spo
t 69
0.26
0.07
620.
0014
0.16
540.
0023
1.73
830.
0338
0.05
600.
0013
0.72
411
0136
987
1310
2313
1100
2490
987
Spo
t 70
0.42
0.09
610.
0012
0.24
790.
0030
3.28
240.
0443
0.07
180.
0012
0.90
615
4922
1428
1614
7711
1401
2292
1549
Spo
t 71
1.17
0.07
660.
0023
0.14
800.
0022
1.56
300.
0464
0.04
210.
0011
0.51
011
1159
890
1395
618
833
2180
890
Spo
t 72
0.45
0.09
750.
0026
0.24
620.
0041
3.31
010.
0873
0.08
260.
0034
0.62
715
7848
1419
2114
8321
1604
6390
1578
Spo
t 73
0.86
0.09
360.
0045
0.16
630.
0029
2.14
490.
1013
0.05
580.
0019
0.37
315
0088
991
1611
6333
1097
3766
991
Spo
t 74
0.36
0.07
860.
0013
0.16
140.
0021
1.74
840.
0312
0.04
800.
0012
0.74
111
6133
965
1210
2712
949
2283
965
Spo
t 75
0.43
0.09
520.
0021
0.22
910.
0032
3.00
610.
0661
0.06
610.
0020
0.62
515
3241
1330
1714
0917
1294
3787
1532
Spo
t 77
0.64
0.10
320.
0013
0.28
500.
0041
4.05
390.
0633
0.07
530.
0011
0.91
616
8223
1617
2016
4513
1468
2096
1682
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
85
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 78
0.42
0.08
140.
0012
0.17
430.
0024
1.95
650.
0328
0.05
680.
0009
0.82
412
3229
1036
1311
0111
1117
1884
1232
Spo
t 80
0.32
0.07
450.
0020
0.15
970.
0024
1.64
110.
0443
0.05
020.
0019
0.55
010
5654
955
1398
617
990
3690
955
Spo
t 81
0.40
0.07
600.
0017
0.15
310.
0020
1.60
300.
0355
0.04
660.
0012
0.59
910
9443
918
1197
114
921
2484
918
Spo
t 82
0.43
0.08
310.
0013
0.19
920.
0026
2.28
100.
0373
0.05
830.
0012
0.78
312
7130
1171
1412
0612
1146
2492
1171
Spo
t 83
0.37
0.07
190.
0019
0.16
200.
0023
1.60
650.
0424
0.04
570.
0016
0.53
198
453
968
1397
317
904
3198
968
Spo
t 84
0.61
0.09
750.
0016
0.23
540.
0031
3.16
500.
0561
0.07
500.
0016
0.75
215
7731
1363
1614
4914
1462
2986
1577
Spo
t 86
0.36
0.07
780.
0020
0.16
440.
0023
1.76
400.
0454
0.05
340.
0018
0.55
311
4250
981
1310
3217
1051
3486
981
Spo
t 87
0.16
0.09
170.
0011
0.24
080.
0030
3.04
390.
0426
0.06
770.
0016
0.90
314
6123
1391
1614
1911
1324
2995
1461
Spo
t 89
0.09
0.09
500.
0012
0.24
700.
0031
3.23
580.
0457
0.10
720.
0027
0.89
515
2923
1423
1614
6611
2057
4993
1529
Spo
t 90
0.22
0.12
080.
0013
0.31
250.
0040
5.20
670.
0696
0.06
550.
0014
0.95
819
6920
1753
2018
5411
1283
2689
1969
Spo
t 93
0.40
0.10
350.
0014
0.27
650.
0037
3.94
640.
0610
0.08
160.
0018
0.85
416
8826
1574
1816
2313
1586
3393
1688
Spo
t 95
0.40
0.09
450.
0012
0.26
610.
0034
3.46
630.
0505
0.07
780.
0016
0.87
315
1825
1521
1715
2011
1514
2910
015
18
Spo
t 96
0.61
0.09
600.
0013
0.25
690.
0037
3.40
120.
0546
0.06
070.
0025
0.90
415
4925
1474
1915
0513
1191
4795
1549
Spo
t 98
0.30
0.11
860.
0015
0.24
350.
0033
3.98
160.
0578
0.09
570.
0021
0.92
219
3622
1405
1716
3012
1848
3973
1936
Spo
t 99
0.41
0.08
070.
0010
0.17
780.
0022
1.97
800.
0274
0.04
260.
0008
0.91
112
1524
1055
1211
089
843
1587
1215
Spo
t 100
0.77
0.09
560.
0012
0.26
540.
0034
3.49
660.
0501
0.07
740.
0015
0.88
615
4024
1518
1715
2711
1506
2899
1540
Spo
t 101
0.30
0.09
420.
0011
0.26
560.
0033
3.44
740.
0467
0.07
430.
0015
0.92
515
1122
1518
1715
1511
1449
2810
015
11
Spo
t 102
0.36
0.07
590.
0026
0.17
490.
0032
1.83
210.
0618
0.05
790.
0059
0.54
210
9268
1039
1810
5722
1138
112
9510
92
Spo
t 103
0.44
0.08
660.
0011
0.23
330.
0029
2.78
390.
0391
0.06
690.
0014
0.89
713
5124
1352
1513
5110
1308
2610
013
51
Spo
t 104
0.33
0.09
590.
001 1
0.26
770.
0034
3.53
920.
0478
0.08
040.
0015
0.93
515
4622
1529
1715
3611
1562
2999
1546
Spo
t 106
0.42
0.10
640.
0014
0.29
280.
0039
4.29
530.
0637
0.08
890.
0022
0.89
917
3923
1656
1916
9312
1721
4195
1739
Spo
t 107
0.50
0.10
790.
0014
0.30
610.
0040
4.55
380.
0652
0.08
640.
0021
0.90
317
6523
1721
2017
4112
1674
3998
1765
Spo
t 112
0.42
0.07
460.
0011
0.16
870.
0021
1.73
400.
0277
0.04
910.
0012
0.79
110
5730
1005
1210
2110
970
2495
1057
Spo
t 113
0.36
0.07
580.
0019
0.16
940.
0024
1.77
010.
0443
0.05
190.
0020
0.57
310
9049
1009
1310
3516
1022
3893
1090
Spo
t 114
0.39
0.08
440.
0018
0.19
400.
0027
2.25
710.
0486
0.06
090.
0019
0.64
613
0241
1143
1511
9915
1195
3688
1302
Spo
t 116
0.20
0.10
240.
0011
0.28
310.
0035
3.99
460.
0515
0.09
060.
0021
0.94
516
6821
1607
1716
3310
1754
4096
1668
Spo
t 119
0.34
0.09
200.
0013
0.24
880.
0033
3.15
480.
0489
0.07
400.
0020
0.84
314
6727
1432
1714
4612
1442
3798
1467
Spo
t 120
0.24
0.09
580.
0011
0.27
180.
0034
3.59
040.
0480
0.07
330.
0016
0.94
715
4521
1550
1715
4711
1431
3010
015
45
Spo
t 121
0.66
0.07
640.
0010
0.17
020.
0023
1.79
320.
0280
0.05
020.
0013
0.86
611
0727
1013
1310
4310
990
2592
1107
Spo
t 122
0.81
0.12
120.
0014
0.34
840.
0044
5.82
280.
0765
0.09
710.
0021
0.95
219
7520
1927
2119
5011
1874
3998
1975
Spo
t 123
0.41
0.07
860.
0014
0.17
090.
0025
1.85
040.
0346
0.04
960.
0019
0.76
711
6234
1017
1310
6412
979
3788
1162
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
86
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 124
0.96
0.10
340.
0012
0.24
850.
0032
3.54
110.
0471
0.07
110.
0014
0.95
316
8620
1431
1615
3611
1389
2785
1686
Spo
t 125
0.10
0.09
560.
0011
0.25
080.
0034
3.30
440.
0473
0.08
450.
0031
0.94
815
4021
1443
1814
8211
1639
5894
1540
Spo
t 127
0.43
0.09
300.
0013
0.27
050.
0034
3.46
680.
0515
0.07
690.
0022
0.85
414
8725
1543
1715
2012
1498
4110
414
87
Spo
t 128
0.42
0.07
310.
0011
0.16
850.
0022
1.69
650.
0272
0.05
230.
0013
0.80
710
1529
1004
1210
0710
1030
2499
1015
Spo
t 129
0.48
0.09
750.
0012
0.27
210.
0035
3.65
620.
0512
0.07
990.
0018
0.90
815
7623
1551
1815
6211
1554
3498
1576
Spo
t 130
1.59
0.08
780.
0014
0.22
770.
0030
2.75
670.
0468
0.06
680.
0015
0.77
913
7830
1323
1613
4413
1306
2896
1378
Spo
t 20.
230.
0826
0.00
140.
2070
0.00
302.
3571
0.04
270.
0671
0.00
150.
7994
2271
912
6032
1213
1612
3013
1313
2896
1260
Spo
t 30.
710.
1099
0.00
140.
3214
0.00
444.
8705
0.07
180.
0812
0.00
110.
9355
7563
917
9823
1797
2217
9712
1578
2110
017
98
Spo
t 50.
250.
1071
0.00
130.
2985
0.00
424.
4052
0.06
580.
0706
0.00
120.
9469
9692
417
5122
1684
2117
1312
1379
2296
1751
Spo
t 71.
260.
0911
0.00
200.
2519
0.00
393.
1630
0.07
120.
0737
0.00
120.
6841
4752
514
4842
1448
2014
4817
1437
2310
014
48
Spo
t 90.
470.
0798
0.00
100.
1902
0.00
272.
0921
0.03
210.
0538
0.00
070.
9295
9580
411
9225
1122
1511
4611
1059
1394
1192
Spo
t 12
0.11
0.09
070.
0012
0.24
160.
0033
3.02
150.
0472
0.07
530.
0018
0.88
4453
573
1441
2613
9517
1413
1214
6833
9714
41
Spo
t 17
0.29
0.09
560.
0010
0.27
820.
0036
3.66
430.
0484
0.07
820.
0009
0.97
4591
376
1539
2015
8218
1564
1115
2117
103
1539
Spo
t 20
0.37
0.08
690.
0011
0.23
000.
0030
2.75
620.
0396
0.06
640.
0009
0.90
4021
296
1359
2413
3416
1344
1112
9917
9813
59
Spo
t 21
0.27
0.08
990.
0011
0.24
830.
0032
3.07
550.
0427
0.07
450.
0010
0.93
7031
715
1423
2214
3017
1427
1114
5219
100
1423
Spo
t 22
0.13
0.09
640.
0012
0.24
780.
0033
3.29
230.
0477
0.08
430.
0016
0.92
1986
826
1555
2314
2717
1479
1116
3629
9215
55
Spo
t 23
1.52
0.09
050.
0011
0.24
800.
0033
3.09
410.
0450
0.06
320.
0008
0.92
0367
5914
3624
1428
1714
3111
1239
1599
1436
Spo
t 24
0.32
0.09
430.
0012
0.25
970.
0038
3.37
580.
0530
0.04
840.
0012
0.93
6804
377
1515
2414
8820
1499
1295
522
9815
15
Spo
t 26
0.28
0.08
130.
0011
0.15
930.
0023
1.78
610.
0286
0.03
940.
0007
0.91
0422
346
1230
2695
313
1040
1078
114
7795
3
Spo
t 29
0.43
0.09
630.
0014
0.26
910.
0037
3.57
230.
0576
0.07
250.
0013
0.85
4794
751
1553
2715
3619
1543
1314
1424
9915
53
Spo
t 31
0.65
0.10
220.
0018
0.27
460.
0041
3.86
700.
0727
0.07
510.
0016
0.79
4575
125
1664
3215
6421
1607
1514
6331
9416
64
Spo
t 32
0.77
0.08
950.
001 1
0.24
230.
0032
2.98
890.
0426
0.06
490.
0007
0.93
5442
305
1414
2313
9917
1405
1112
7214
9914
14
Spo
t 33
0.49
0.09
820.
0014
0.27
050.
0037
3.66
040.
0583
0.07
440.
0012
0.86
7882
956
1590
2615
4319
1563
1314
5022
9715
90
Spo
t 34
0.58
0.09
450.
0011
0.25
690.
0034
3.34
670.
0455
0.06
980.
0008
0.96
2095
681
1518
2114
7417
1492
1113
6314
9715
18
Spo
t 35
0.39
0.08
760.
0012
0.22
410.
0030
2.70
640.
0422
0.06
180.
0010
0.84
7547
284
1373
2713
0416
1330
1212
1218
9513
73
Spo
t 36
0.11
0.13
340.
0014
0.27
540.
0039
5.06
350.
0715
0.09
230.
0018
0.98
6402
358
2143
1815
6820
1830
1217
8432
7321
43
Spo
t 37
0.30
0.08
430.
0013
0.19
960.
0028
2.31
840.
0399
0.06
270.
0012
0.80
1720
498
1299
3111
7315
1218
1212
3023
9012
99
Spo
t 39
0.30
0.08
570.
0013
0.22
620.
0031
2.67
330.
0447
0.05
940.
0011
0.82
7172
364
1332
2913
1516
1321
1211
6622
9913
32
Spo
t 40
0.32
0.11
180.
0014
0.31
410.
0042
4.84
200.
0711
0.08
280.
0013
0.91
4664
727
1829
2317
6121
1792
1216
0824
9618
29
Spo
t 43
0.58
0.06
690.
0013
0.08
580.
0012
0.79
130.
0164
0.02
370.
0005
0.69
8815
125
835
4153
17
592
947
410
6453
1
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
Sam
ple
BD
M-0
1
87
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 44
0.66
0.09
430.
0013
0.26
360.
0036
3.42
770.
0532
0.06
750.
0010
0.88
3333
507
1515
2515
0818
1511
1213
2118
100
1515
Spo
t 45
0.85
0.37
220.
0037
0.09
460.
0012
4.85
260.
0614
0.08
160.
0010
0.97
2895
238
0115
583
717
9411
1585
1815
583
Spo
t 49
0.85
0.11
330.
0018
0.32
170.
0045
5.02
220.
0857
0.08
500.
0013
0.82
7042
857
1852
2817
9822
1823
1416
4924
9718
52
Spo
t 50
0.34
0.08
690.
0013
0.22
340.
0033
2.67
930.
0467
0.05
620.
0013
0.85
7342
323
1359
2913
0018
1323
1311
0524
9613
59
Spo
t 51
0.56
0.13
120.
0017
0.33
250.
0048
6.01
470.
0919
0.09
530.
0015
0.94
2417
109
2114
2218
5123
1978
1318
4128
8821
14
Spo
t 53
0.67
0.08
030.
0011
0.19
640.
0027
2.17
490.
0335
0.05
260.
0010
0.88
0434
149
1204
2611
5614
1173
1110
3719
9612
04
Spo
t 54
0.44
0.06
160.
0009
0.10
490.
0014
0.89
110.
0145
0.02
880.
0005
0.82
4746
836
661
3164
38
647
857
310
9764
3
Spo
t 55
0.60
0.06
150.
0029
0.08
630.
0016
0.73
090.
0332
0.02
530.
0014
0.41
8058
717
656
9853
310
557
2050
527
8153
3
Spo
t 56
0.34
0.23
940.
0024
0.10
380.
0014
3.42
610.
0440
0.12
510.
0013
0.98
1085
796
3116
1663
78
1510
1023
8324
2063
7
Spo
t 57
0.60
0.11
200.
0017
0.30
740.
0043
4.74
430.
0793
0.07
940.
0014
0.83
8482
3218
3128
1728
2117
7514
1545
2794
1831
Spo
t 58
0.47
0.11
660.
0013
0.32
920.
0044
5.29
280.
0709
0.08
650.
0010
0.98
6689
427
1905
1918
3521
1868
1116
7719
9619
05
Spo
t 59
0.52
0.10
830.
0012
0.30
890.
0040
4.61
150.
0599
0.07
880.
0010
0.98
5429
739
1771
2017
3519
1751
1115
3419
9817
71
Spo
t 62
0.51
0.10
860.
0014
0.30
580.
0040
4.57
680.
0655
0.07
930.
0012
0.91
8419
317
1775
2317
2020
1745
1215
4323
9717
75
Spo
t 65
0.40
0.06
610.
0015
0.08
490.
0012
0.77
320.
0168
0.02
760.
0016
0.62
2240
052
810
4552
57
582
1054
931
6552
5
Spo
t 65b
0.29
0.09
790.
0016
0.07
710.
0012
1.03
890.
0189
0.03
090.
0010
0.86
2313
8115
8430
479
772
39
615
2030
479
Spo
t 69
0.44
0.11
270.
0014
0.31
040.
0046
4.81
410.
0757
0.08
450.
0021
0.94
4841
111
1843
2317
4323
1787
1316
3939
9518
43
Spo
t 70
0.38
0.10
050.
0013
0.26
710.
0041
3.69
270.
0605
0.06
720.
0022
0.93
1615
609
1633
2415
2621
1570
1313
1542
9316
33
Spo
t 71
0.40
0.06
350.
0013
0.08
730.
0013
0.76
380.
0163
0.02
910.
0008
0.68
8633
325
725
4254
08
576
958
015
7454
0
Spo
t 76
0.11
0.20
520.
0022
0.10
430.
0013
2.94
960.
0377
0.26
800.
0042
0.98
2779
9628
6818
640
813
9510
4799
6722
640
Spo
t 77
0.38
0.08
150.
001 1
0.20
760.
0028
2.33
110.
0357
0.06
120.
0010
0.88
3712
353
1233
2612
1615
1222
1112
0119
9912
33
Spo
t 78
0.33
0.08
170.
0011
0.20
840.
0028
2.34
670.
0364
0.06
110.
0011
0.86
2922
167
1238
2712
2015
1227
1111
9920
9912
38
Spo
t 81
0.41
0.10
970.
0014
0.32
680.
0044
4.94
030.
0716
0.09
320.
0015
0.91
8728
123
1794
2318
2321
1809
1218
0028
102
1794
Spo
t 83
0.47
0.10
930.
0013
0.32
310.
0043
4.86
770.
0690
0.09
300.
0014
0.93
4851
4717
8822
1805
2117
9712
1797
2610
117
88
Spo
t 85
0.31
0.09
650.
0011
0.27
480.
0036
3.65
410.
0493
0.07
750.
0011
0.96
3031
078
1557
2115
6518
1561
1115
0921
101
1557
Spo
t 86
0.21
0.07
570.
0010
0.17
650.
0024
1.84
000.
0275
0.05
370.
0011
0.91
6616
738
1086
2510
4813
1060
1010
5720
9610
86
Spo
t 89
0.82
0.09
830.
0014
0.27
630.
0038
3.74
460.
0612
0.08
050.
0013
0.85
0841
627
1593
2715
7319
1581
1315
6525
9915
93
Spo
t 91
0.31
0.08
260.
0010
0.19
900.
0027
2.26
840.
0322
0.05
880.
0008
0.94
2340
674
1261
2311
7014
1203
1011
5415
9312
61
Spo
t 94
0.80
0.06
130.
0009
0.10
290.
0014
0.86
920.
0140
0.03
000.
0004
0.83
1207
785
649
3063
18
635
859
88
9763
1
Spo
t 98
0.37
0.26
130.
0027
0.08
870.
0013
3.19
610.
0453
0.11
460.
0013
0.98
2183
993
3255
1654
88
1456
1121
9223
1754
8
Spo
t 104
0.66
0.05
980.
0014
0.09
140.
0014
0.75
320.
0182
0.02
430.
0008
0.64
3245
776
597
5056
48
570
1148
616
9456
4
Spo
t 105
0.45
0.11
210.
0013
0.18
900.
0026
2.92
100.
0413
0.06
080.
0008
0.97
6371
418
1833
2011
1614
1387
1111
9415
6118
33
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
88
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Anal
ysis
Th/U
207 Pb
/206 Pb
± 1σ
206 Pb
/238 U
± 1σ
207 Pb
/235 U
± 1σ
208 Pb
/232 Th
± 1σ
Rho
b20
7 Pb/20
6 Pb±
1σ20
6 Pb/23
8 U±
1σ20
7 Pb/23
5 U±
1σ20
8 Pb/23
2 Th±
1σC
onc.
c
Spot
114
0.64
0.09
140.
0011
0.08
800.
0011
1.10
890.
0155
0.03
800.
0005
0.91
3113
559
1455
2354
47
758
775
59
3754
4
Spot
115
0.11
0.32
370.
0032
0.08
160.
0011
3.64
310.
0479
0.45
210.
0050
0.97
5100
651
3587
1550
67
1559
1075
3969
1450
6
Spot
117
0.41
0.09
870.
0011
0.24
070.
0034
3.27
550.
0477
0.07
710.
0010
0.97
0884
075
1599
2113
9118
1475
1115
0119
8715
99
Spot
118
0.08
0.32
090.
0032
0.08
470.
0012
3.74
880.
0528
0.50
440.
0057
0.97
0626
875
3574
1552
47
1582
1182
5577
1552
4
Spot
121
1.07
0.06
240.
0008
0.10
620.
0015
0.91
310.
0139
0.02
980.
0004
0.90
5823
059
688
2665
19
659
759
47
9565
1
Spot
124
0.09
0.24
230.
0025
0.06
590.
0009
2.19
910.
0292
0.26
820.
0030
0.99
2595
855
3135
1641
15
1181
948
0348
1341
1
Spot
130
0.19
0.09
490.
0011
0.18
090.
0026
2.36
620.
0345
0.08
240.
0011
0.96
9292
446
1526
2110
7214
1233
1016
0021
7015
26
Spot
131
0.42
0.11
180.
0012
0.32
440.
0044
5.00
040.
0681
0.08
850.
0011
0.98
4224
145
1829
1918
1121
1819
1217
1420
9918
29
Spot
133
0.72
0.09
890.
0014
0.21
770.
0031
2.96
680.
0500
0.06
970.
0009
0.83
4289
126
1603
2712
7016
1399
1313
6316
7916
03
Spot
137
0.13
0.35
150.
0035
0.05
970.
0008
2.89
360.
0382
0.26
440.
0028
0.98
5230
784
3713
1537
45
1380
1047
4245
1037
4
Spot
140
0.30
0.24
580.
0025
0.08
990.
0012
3.04
580.
0402
0.11
720.
0013
0.98
8454
631
3158
1655
57
1419
1022
3923
1855
5
Spot
141
0.57
0.08
640.
0017
0.21
040.
0032
2.50
530.
0523
0.05
510.
0011
0.73
8332
656
1347
3712
3117
1274
1510
8422
9113
47
Spot
142
1.36
0.11
470.
0014
0.33
690.
0046
5.32
750.
0763
0.08
430.
0010
0.95
1131
9918
7521
1872
2218
7312
1636
1810
018
75
Spot
143
0.41
0.08
280.
0016
0.22
940.
0033
2.61
930.
0541
0.06
250.
0014
0.70
2676
1512
6538
1331
1713
0615
1225
2710
512
65
Spot
150
0.08
0.13
570.
0015
0.11
320.
0015
2.11
780.
0287
0.16
250.
0018
0.98
9453
391
2173
1969
19
1155
930
4332
3269
1
Spot
151
0.35
0.09
930.
0011
0.25
940.
0034
3.55
100.
0473
0.06
840.
0008
0.98
6151
0916
1120
1487
1715
3911
1338
1492
1611
Spot
154
0.62
0.11
890.
0029
0.11
160.
0017
1.82
830.
0423
0.03
180.
0009
0.65
4231
327
1940
4268
210
1056
1563
317
3568
2
Spot
156
0.53
0.05
950.
0013
0.08
530.
0012
0.69
940.
0153
0.02
240.
0004
0.62
8328
497
585
4552
87
538
944
99
9052
8
Spot
159
0.30
0.08
410.
0012
0.21
180.
0028
2.45
430.
0388
0.05
760.
0011
0.83
0971
283
1294
2812
3915
1259
1111
3220
9612
94
Spot
161
0.49
0.07
310.
0010
0.16
020.
0022
1.61
520.
0253
0.04
150.
0006
0.87
2427
668
1018
2795
812
976
1082
111
9495
8
Spot
163
0.20
0.19
600.
0020
0.09
730.
0012
2.62
790.
0333
0.15
680.
0016
0.99
6806
314
2793
1759
87
1309
929
4528
2159
8
Spot
164
0.46
0.11
150.
0017
0.30
000.
0043
4.61
220.
0779
0.07
750.
0014
0.85
6625
263
1824
2716
9222
1752
1415
0826
9318
24
Spot
165
0.48
0.11
750.
0013
0.32
800.
0042
5.31
200.
0697
0.08
400.
0009
0.97
8218
773
1918
1918
2920
1871
1116
3117
9519
18
Spot
166
0.48
0.10
090.
0011
0.27
060.
0035
3.76
280.
0488
0.06
890.
0007
0.98
6446
269
1640
1915
4418
1585
1013
4613
9416
40
Spot
170
0.39
0.13
450.
0017
0.15
840.
0023
2.93
750.
0450
0.05
650.
0009
0.94
7032
457
2158
2294
813
1392
1211
1118
4494
8
Spot
172
0.50
0.09
670.
0011
0.25
740.
0033
3.43
030.
0456
0.07
010.
0008
0.96
5530
488
1561
2114
7717
1511
1013
6915
9515
61
Spot
173
0.21
0.07
860.
0009
0.20
040.
0025
2.17
180.
0285
0.05
690.
0007
0.96
3068
471
1163
2211
7814
1172
911
1814
101
1163
Spot
174
0.57
0.14
480.
0019
0.19
060.
0027
3.80
260.
0581
0.09
230.
0016
0.93
3419
124
2285
2211
2515
1593
1217
8429
4922
85
Spot
175
0.48
0.07
550.
0008
0.14
130.
0018
1.47
080.
0193
0.03
860.
0004
0.96
1776
416
1082
2285
210
918
876
69
7985
2
Spot
176
0.27
0.08
790.
0012
0.22
970.
0028
2.78
210.
0394
0.06
310.
0012
0.86
3416
509
1379
2513
3315
1351
1112
3623
9713
79
Spot
177
0.40
0.08
570.
0009
0.22
040.
0028
2.60
410.
0342
0.05
640.
0006
0.97
7062
784
1332
2112
8415
1302
1011
0812
9613
32
Isot
opic
Rat
iosa
Age
Estim
ates
a (Ma)
Eff.
Aged
89
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 180
0.37
0.09
020.
0015
0.25
080.
0034
3.11
750.
0538
0.07
370.
0016
0.79
5288
6314
2930
1443
1814
3713
1437
3010
114
29
Spo
t 182
0.20
0.42
750.
0043
0.05
670.
0007
3.33
860.
0417
0.23
870.
0027
0.98
2746
906
4009
1535
54
1490
1043
2744
935
5
Spo
t 183
0.19
0.07
300.
0010
0.17
390.
0023
1.75
060.
0273
0.05
110.
0010
0.82
9383
904
1015
2910
3412
1027
1010
0720
102
1015
Spo
t 184
0.23
0.07
400.
0009
0.17
080.
0023
1.74
250.
0252
0.04
310.
0006
0.93
2178
603
1042
2410
1713
1024
985
312
9810
42
Spo
t 185
0.21
0.11
960.
0012
0.36
250.
0047
5.97
430.
0769
0.09
050.
0011
0.99
8954
953
1950
1819
9422
1972
1117
5021
102
1950
Spo
t 187
0.53
0.06
300.
0015
0.09
890.
0014
0.85
910.
0208
0.02
810.
0006
0.57
5154
986
708
5060
88
630
1155
912
8660
8
Spo
t 188
0.80
0.05
690.
0023
0.08
870.
0015
0.69
610.
0280
0.02
520.
0007
0.41
1690
1248
988
548
953
617
502
1411
254
8
Spo
t 188
b1.
100.
0587
0.00
390.
0897
0.00
180.
7258
0.04
700.
0276
0.00
090.
3046
9632
655
413
855
410
554
2855
118
100
554
Spo
t 189
0.52
0.08
760.
0012
0.24
940.
0037
3.01
270.
0497
0.05
190.
0011
0.88
9107
519
1374
2714
3619
1411
1310
2221
104
1374
Spo
t 194
0.27
0.09
350.
0010
0.26
830.
0036
3.45
870.
0469
0.06
870.
0010
0.98
4987
613
1498
2015
3218
1518
1113
4318
102
1498
Spo
t 195
0.56
0.11
030.
0013
0.32
270.
0042
4.90
800.
0670
0.08
480.
0011
0.95
3791
948
1805
2118
0320
1804
1216
4520
100
1805
Spo
t 198
0.38
0.07
470.
0011
0.17
500.
0023
1.80
170.
0287
0.04
880.
0008
0.81
7529
974
1060
2910
4012
1046
1096
315
9810
60
Spo
t 10.
430.
0822
0.00
160.
2130
0.00
292.
4128
0.04
740.
0639
0.00
150.
6936
1249
3712
4515
1246
1412
5328
100
1249
Spo
t 30.
300.
0746
0.00
210.
1657
0.00
251.
7032
0.04
650.
0548
0.00
200.
5571
1057
5598
814
1010
1710
7938
9398
8
Spo
t 4b
0.69
0.09
300.
0016
0.26
110.
0035
3.34
760.
0598
0.08
120.
0015
0.75
7414
8832
1496
1814
9214
1577
2810
114
88
Spo
t 50.
310.
0709
0.00
180.
1556
0.00
231.
5187
0.03
780.
0505
0.00
160.
5994
954
5093
213
938
1599
531
9893
2
Spo
t 90.
370.
2559
0.00
420.
2105
0.00
317.
4260
0.12
180.
2712
0.00
510.
8889
3222
2612
3116
2164
1548
5181
3832
22
Spo
t 10
0.68
0.18
750.
0032
0.22
280.
0032
5.75
760.
0980
0.12
740.
0025
0.84
4127
2128
1296
1719
4015
2424
4548
2721
Spo
t 11
0.26
0.13
860.
0021
0.18
630.
0025
3.56
000.
0579
0.14
610.
0028
0.83
2522
1026
1101
1415
4113
2756
5050
2210
Spo
t 12
0.44
0.21
950.
0056
0.23
130.
0041
6.99
870.
1688
0.20
260.
0058
0.73
1329
7740
1341
212 1
1121
3728
9745
2977
Spo
t 13
0.51
0.09
910.
0028
0.20
460.
0032
2.79
440.
0767
0.07
760.
0024
0.56
8216
0751
1200
1713
5421
1511
4575
1607
Spo
t 15
0.48
0.07
870.
0013
0.20
660.
0030
2.24
080.
0420
0.06
270.
0011
0.78
6111
6433
1211
1611
9413
1230
2110
411
64
Spo
t 16
0.45
0.10
280.
0017
0.23
670.
0032
3.35
560.
0574
0.08
600.
0018
0.78
3516
7630
1370
1714
9413
1668
3482
1676
Spo
t 17
0.25
0.10
140.
0012
0.25
590.
0032
3.57
480.
0491
0.08
870.
0017
0.91
1316
4922
1469
1615
4411
1717
3189
1649
Spo
t 18
0.30
0.08
730.
0016
0.19
980.
0027
2.40
400.
0447
0.06
750.
0018
0.71
9613
6734
1174
1412
4413
1321
3486
1367
Spo
t 20
0.34
0.07
790.
0016
0.21
220.
0029
2.27
810.
0480
0.06
950.
0019
0.65
1211
4341
1241
1512
0615
1358
3710
911
43
Spo
t 21
0.56
0.13
780.
0021
0.18
320.
0026
3.47
950.
0575
0.10
210.
0024
0.86
5722
0026
1085
1415
2313
1965
4449
2200
Spo
t 23
0.41
0.08
430.
0014
0.22
800.
0031
2.65
070.
0466
0.06
940.
0015
0.76
0313
0032
1324
1613
1513
1356
2910
213
00
Spo
t 24
0.52
0.07
380.
0029
0.15
630.
0027
1.59
070.
0616
0.04
580.
0020
0.45
0910
3678
936
1596
724
904
3890
1036
Spo
t 26
0.25
0.07
660.
0014
0.18
260.
0025
1.92
710.
0367
0.05
730.
0016
0.70
3711
0936
1081
1310
9113
1127
3197
1109
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
Sam
ple
BS
A-0
7
90
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 26b
0.23
0.08
080.
0025
0.18
270.
0028
2.03
440.
0613
0.06
430.
0032
0.50
7212
1758
1082
1511
2721
1260
6089
1217
Spo
t 27
0.54
0.07
220.
0014
0.17
450.
0023
1.73
590.
0342
0.05
710.
0014
0.66
8499
139
1037
1310
2213
1123
2610
599
1
Spo
t 28
0.74
0.09
180.
0012
0.25
670.
0033
3.24
980.
0461
0.07
380.
0015
0.89
7814
6424
1473
1714
6911
1439
2810
114
64
Spo
t 30
0.24
0.07
420.
0011
0.16
940.
0022
1.73
240.
0277
0.05
230.
0013
0.81
2610
4629
1009
1210
2110
1030
2696
1046
Spo
t 31
0.33
0.09
060.
0016
0.25
560.
0036
3.19
240.
0596
0.08
070.
0024
0.74
7814
3933
1467
1814
5514
1568
4510
214
39
Spo
t 34
0.32
0.07
130.
0017
0.14
950.
0021
1.47
010.
0345
0.04
970.
0016
0.59
5296
646
898
1291
814
980
3093
966
Spo
t 36
0.24
0.07
940.
0013
0.19
560.
0025
2.14
040.
0362
0.06
230.
0022
0.75
3311
8132
1152
1311
6212
1221
4297
1181
Spo
t 37
0.41
0.08
670.
0021
0.22
380.
0032
2.67
340.
0633
0.06
980.
0026
0.60
5913
5345
1302
1713
2118
1364
4996
1353
Spo
t 39
0.26
0.07
860.
0010
0.20
020.
0026
2.16
960.
0308
0.06
240.
0014
0.89
6911
6325
1176
1411
7110
1223
2710
111
63
Spo
t 40
0.49
0.08
860.
0016
0.22
960.
0031
2.80
500.
0531
0.07
020.
0019
0.72
2613
9634
1332
1613
5714
1371
3695
1396
Spo
t 41
0.23
0.08
540.
0012
0.22
550.
0029
2.65
360.
0399
0.06
970.
0018
0.86
1613
2426
1311
1513
1611
1361
3599
1324
Spo
t 44
0.47
0.07
790.
0012
0.17
110.
0023
1.83
790.
0310
0.04
500.
0011
0.78
7711
4431
1018
1310
5911
889
2289
1144
Spo
t 45
0.33
0.07
190.
0021
0.15
280.
0023
1.51
470.
0447
0.05
390.
0021
0.50
1898
459
917
1393
618
1062
4093
984
Spo
t 46
0.43
0.08
240.
0014
0.20
570.
0027
2.33
600.
0413
0.06
460.
0018
0.75
0912
5532
1206
1512
2313
1265
3396
1255
Spo
t 47
0.31
0.08
060.
0012
0.21
160.
0027
2.34
990.
0380
0.06
460.
0018
0.80
1612
1129
1237
1512
2812
1266
3410
212
11
Spo
t 48
0.38
0.07
270.
0010
0.16
810.
0021
1.68
550.
0249
0.05
130.
0012
0.85
7310
0627
1002
1210
039
1012
2410
010
06
Spo
t 49
0.36
0.07
540.
0014
0.17
800.
0024
1.84
980.
0351
0.05
850.
0018
0.71
6210
7836
1056
1310
6313
1149
3498
1078
Spo
t 50
0.65
0.08
350.
0022
0.20
280.
0030
2.33
510.
0626
0.06
870.
0022
0.55
5812
8152
1190
1612
2319
1344
4193
1281
Spo
t 51
0.50
0.07
240.
0022
0.15
170.
0023
1.51
490.
0451
0.05
060.
0018
0.50
0099
859
911
1393
618
997
3491
911
Spo
t 52
0.40
0.09
030.
0037
0.20
400.
0040
2.54
150.
1024
0.07
090.
0042
0.48
4114
3277
1 197
2112
8429
1384
8084
1432
Spo
t 53
0.21
0.08
150.
0009
0.21
480.
0031
2.41
440.
0367
0.06
180.
0009
0.96
1312
3423
1254
1712
4711
1211
1710
212
34
Spo
t 54
0.63
0.09
710.
0016
0.26
770.
0046
3.57
990.
0699
0.05
790.
0012
0.88
7515
6830
1529
2415
4516
1137
2397
1568
Spo
t 55
0.40
0.07
810.
0011
0.20
960.
0027
2.25
760.
0335
0.06
710.
0017
0.85
4811
5026
1227
1411
9910
1313
3210
711
50
Spo
t 56
0.98
0.07
320.
0017
0.17
860.
0025
1.80
300.
0424
0.05
730.
0015
0.59
5310
2046
1059
1410
4715
1127
2910
410
20
Spo
t 58
0.62
0.07
770.
0015
0.17
370.
0024
1.86
020.
0377
0.05
830.
0016
0.67
2811
3939
1032
1310
6713
1146
3191
1139
Spo
t 59
0.29
0.08
890.
0010
0.24
270.
0036
2.97
280.
0457
0.07
410.
0010
0.95
9314
0122
1401
1914
0112
1444
2010
014
01
Spo
t 60
0.54
0.06
270.
0021
0.10
630.
0016
0.91
880.
0306
0.03
720.
0014
0.44
8769
870
651
966
216
738
2793
651
Spo
t 60b
0.47
0.06
120.
0022
0.10
560.
0016
0.89
090.
0314
0.03
490.
0012
0.42
4164
675
647
964
717
693
2410
064
7
Spo
t 60b
0.46
0.07
930.
0014
0.19
210.
0026
2.09
920.
0381
0.05
840.
0016
0.73
1711
7934
1133
1411
4912
1146
3196
1179
Spo
t 60b
0.29
0.07
980.
0013
0.17
720.
0027
1.94
830.
0363
0.05
600.
0011
0.82
0011
9132
1052
1510
9813
1100
2288
1191
Spo
t 64
0.50
0.07
440.
0014
0.17
440.
0023
1.78
790.
0342
0.05
270.
0014
0.69
1510
5137
1037
1310
4112
1038
2799
1051
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
91
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 67
0.57
0.09
140.
0011
0.24
470.
0036
3.08
140.
0476
0.06
900.
0009
0.95
5614
5422
1411
1914
2812
1349
1797
1454
Spo
t 70
0.46
0.08
590.
0014
0.22
160.
0037
2.62
340.
0515
0.05
680.
0011
0.85
9213
3631
1290
2013
0714
1117
2197
1336
Spo
t 73
0.50
0.09
600.
0011
0.26
720.
0041
3.53
590.
0553
0.07
880.
0010
0.97
5715
4721
1527
2115
3512
1534
2099
1547
Spo
t 74
0.30
0.08
690.
0013
0.22
620.
0029
2.71
000.
0429
0.06
890.
0020
0.80
4313
5928
1314
1513
3112
1347
3897
1359
Spo
t 75
0.42
0.08
210.
0020
0.19
940.
0029
2.25
690.
0552
0.05
780.
0022
0.58
6412
4947
1172
1511
9917
1136
4294
1249
Spo
t 76
0.32
0.07
900.
0025
0.19
640.
0031
2.13
860.
0663
0.06
480.
0028
0.50
0911
7260
1156
1611
6121
1269
5499
1172
Spo
t 77
0.43
0.09
180.
0015
0.24
220.
0032
3.06
600.
0520
0.07
060.
0019
0.77
9714
6430
1398
1714
2413
1379
3596
1464
Spo
t 78
0.63
0.09
590.
0013
0.26
600.
0035
3.51
570.
0535
0.07
340.
0020
0.87
2015
4525
1520
1815
3112
1432
3798
1545
Spo
t 79
0.47
0.08
150.
0013
0.19
880.
0028
2.23
400.
0380
0.05
210.
0026
0.82
5812
3530
1169
1511
9212
1027
5195
1235
Spo
t 80
0.47
0.07
780.
0022
0.15
120.
0022
1.62
260.
0464
0.05
050.
0017
0.51
7911
4256
908
1397
918
995
3379
908
Spo
t 81
0.47
0.09
320.
0013
0.24
430.
0036
3.14
100.
0508
0.07
400.
0011
0.90
0614
9325
1409
1814
4312
1443
2194
1493
Spo
t 84
0.36
0.07
310.
0021
0.14
880.
0026
1.49
950.
0434
0.04
920.
0016
0.59
2710
1657
894
1493
018
970
3188
1016
Spo
t 86
0.34
0.08
160.
0010
0.21
490.
0032
2.41
840.
0383
0.06
560.
0009
0.93
2312
3724
1255
1712
4811
1285
1810
112
37
Spo
t 88
0.38
0.07
330.
0012
0.15
500.
0024
1.56
740.
0291
0.04
920.
0009
0.84
0010
2331
929
1495
712
971
1791
929
Spo
t 89
0.23
0.09
520.
0012
0.20
450.
0032
2.68
270.
0449
0.08
110.
0014
0.93
4615
3124
1199
1713
2412
1577
2578
1531
Spo
t 91
0.26
0.07
490.
0013
0.17
310.
0027
1.78
700.
0345
0.05
810.
0013
0.80
1310
6534
1029
1510
4113
1141
2497
1065
Spo
t 94
0.53
0.09
600.
0012
0.26
050.
0039
3.44
730.
0553
0.07
850.
0011
0.93
8815
4723
1493
2015
1513
1527
2096
1547
Spo
t 95
0.55
0.11
140.
0028
0.15
980.
0024
2.45
510.
0610
0.06
320.
0020
0.60
7218
2345
956
1312
5918
1238
3852
956
Spo
t 98
0.56
0.06
240.
0007
0.10
810.
0016
0.92
980.
0143
0.03
490.
0004
0.96
4468
724
662
966
88
694
896
662
Spo
t 101
0.31
0.07
960.
0009
0.19
050.
0028
2.08
940.
0321
0.06
120.
0008
0.97
021 1
8622
1124
1511
4511
1200
1595
1186
Spo
t 103
0.54
0.11
130.
0013
0.27
030.
0034
4.14
870.
0547
0.08
120.
0019
0.94
2418
2121
1542
1716
6411
1577
3685
1821
Spo
t 104
1.18
0.10
310.
0016
0.25
000.
0036
3.54
970.
0615
0.06
970.
0044
0.82
6216
8029
1438
1815
3814
1361
8386
1680
Spo
t 105
0.47
0.07
810.
0011
0.18
130.
0028
1.95
310.
0333
0.05
590.
0008
0.89
2111
5027
1074
1511
0011
1099
1693
1150
Spo
t 106
0.41
0.07
270.
0023
0.16
610.
0026
1.66
500.
0515
0.05
190.
0023
0.50
0310
0662
991
1499
520
1023
4498
991
Spo
t 107
0.89
0.07
520.
0016
0.18
410.
0025
1.90
680.
0409
0.05
660.
0017
0.63
8010
7242
1089
1410
8414
1113
3310
210
72
Spo
t 107
b0.
540.
0742
0.00
100.
1803
0.00
231.
8450
0.02
670.
0552
0.00
160.
8629
1048
2610
6812
1062
1010
8531
102
1048
Spo
t 108
0.32
0.07
150.
0016
0.16
660.
0023
1.64
200.
0374
0.05
050.
0018
0.60
8197
145
993
1398
714
996
3510
299
3
Spo
t 109
0.44
0.07
900.
0022
0.17
400.
0026
1.89
590.
0534
0.05
560.
0023
0.52
6111
7355
1034
1410
8019
1093
4588
1173
Spo
t 110
0.32
0.08
810.
0021
0.23
730.
0034
2.88
260.
0675
0.07
100.
0030
0.61
4113
8544
1373
1813
7718
1386
5799
1385
Spo
t 111
0.57
0.07
870.
0013
0.14
920.
0023
1.61
850.
0306
0.04
820.
0008
0.82
1511
6432
896
1397
712
951
1577
896
Spo
t 112
0.34
0.08
040.
0019
0.20
720.
0030
2.29
690.
0557
0.06
680.
0028
0.58
6712
0747
1214
1612
1117
1306
5310
112
07
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
92
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 113
0.57
0.08
280.
0015
0.19
670.
0033
2.24
640.
0458
0.05
760.
0011
0.81
5912
6634
1157
1811
9614
1131
2091
1266
Spo
t 114
0.51
0.07
620.
0014
0.17
450.
0023
1.83
190.
0353
0.05
420.
0017
0.69
6410
9937
1037
1310
5713
1067
3294
1099
Spo
t 115
0.27
0.07
230.
0013
0.14
970.
0024
1.49
150.
0300
0.05
000.
0011
0.77
9999
436
899
1392
712
986
2190
899
Spo
t 117
0.37
0.07
320.
0018
0.14
650.
0025
1.47
720.
0381
0.04
650.
0013
0.65
1710
1849
881
1492
116
919
2587
881
Spo
t 120
0.39
0.07
830.
0017
0.19
470.
0027
2.10
260.
0465
0.05
780.
0020
0.62
7111
5542
1147
1511
5015
1136
3899
1155
Spo
t 121
0.37
0.07
620.
0009
0.16
910.
0025
1.77
640.
0276
0.05
210.
0007
0.96
4711
0023
1007
1410
3710
1026
1392
1100
Spo
t 123
0.54
0.10
090.
0014
0.27
020.
0036
3.75
950.
0588
0.07
810.
0026
0.85
0016
4126
1542
1815
8413
1519
5094
1641
Spo
t 126
0.50
0.08
700.
0013
0.22
320.
0029
2.67
860.
0438
0.06
620.
0019
0.79
9513
6129
1299
1513
2312
1296
3695
1361
Spo
t 127
0.25
0.08
130.
0013
0.20
480.
0030
2.29
560.
0404
0.06
290.
0014
0.83
7812
2830
1201
1612
1112
1232
2698
1228
Spo
t 129
0.35
0.08
120.
0036
0.17
080.
0034
1.91
270.
0839
0.05
750.
0030
0.45
5312
2685
1017
1910
8629
1129
5783
1226
Spo
t 130
0.31
0.07
190.
0015
0.16
100.
0025
1.59
500.
0360
0.04
970.
0013
0.69
3798
243
962
1496
814
981
2598
962
Spo
t 134
0.34
0.09
490.
0018
0.22
690.
0035
2.96
730.
0614
0.06
770.
0018
0.75
1315
2536
1318
1913
9916
1324
3386
1525
Spo
t 137
0.33
0.08
230.
0020
0.18
210.
0030
2.06
710.
0520
0.05
510.
0018
0.64
3812
5347
1078
1611
3817
1085
3486
1253
Spo
t 138
0.28
0.07
880.
0017
0.18
380.
0029
1.99
660.
0457
0.05
530.
0017
0.68
1911
6643
1088
1611
1415
1088
3293
1166
Spo
t 139
0.62
0.08
700.
0017
0.21
060.
0032
2.52
650.
0518
0.06
090.
0012
0.75
1113
6136
1232
1712
8015
1196
2391
1361
Spo
t 147
0.57
0.08
280.
0015
0.18
970.
0029
2.16
500.
0433
0.05
750.
0011
0.76
9012
6435
1120
1611
7014
1131
2089
1264
Spo
t 149
0.27
0.07
970.
0012
0.18
390.
0027
2.01
960.
0340
0.05
710.
001 1
0.85
5611
8928
1088
1411
2211
1123
2092
1189
Spo
t 150
0.28
0.07
990.
0010
0.19
710.
0029
2.17
000.
0337
0.05
730.
0008
0.94
2311
9324
1160
1611
7211
1126
1697
1193
Spo
t 151
0.58
0.09
330.
0014
0.25
270.
0038
3.25
070.
0564
0.07
250.
0011
0.86
4914
9428
1453
1914
6913
1415
2297
1494
Spo
t 152
0.20
0.07
050.
0010
0.15
220.
0022
1.47
990.
0243
0.04
540.
0008
0.89
5494
327
913
1392
210
897
1697
913
Spo
t 155
1.04
0.12
950.
0015
0.37
720.
0055
6.73
240.
1003
0.09
980.
0011
0.98
4220
9120
2063
2620
7713
1923
2199
2091
Spo
t 161
0.27
0.07
420.
0010
0.16
530.
0024
1.69
050.
0276
0.04
800.
0008
0.89
3210
4627
986
1310
0510
948
1694
986
Spo
t 162
0.29
0.07
000.
0010
0.15
070.
0022
1.45
470.
0245
0.04
340.
0007
0.88
4592
928
905
1391
210
860
1497
905
Spo
t 164
2.43
0.12
100.
0015
0.34
560.
0051
5.76
540.
0891
0.09
150.
0010
0.95
6519
7121
1913
2519
4113
1770
1997
1971
Spo
t 167
0.61
0.11
420.
0013
0.33
670.
0050
5.30
150.
0795
0.08
780.
0011
0.98
1018
6720
1871
2418
6913
1701
2010
018
67
Spo
t 20.
380.
0783
0.00
140.
1952
0.00
302.
1067
0.04
100.
0562
0.00
110.
7930
1153
3411
5016
1151
1311
0622
100
1153
Spo
t 60.
300.
0796
0.00
100.
2020
0.00
282.
2170
0.03
340.
0578
0.00
080.
9313
1188
2411
8615
1186
1111
3616
100
1188
Spo
t 10
0.28
0.08
950.
0010
0.23
050.
0034
2.84
350.
0435
0.06
770.
0010
0.95
6114
1422
1337
1813
6711
1324
1895
1414
Spo
t 12
0.31
0.08
250.
0010
0.19
930.
0029
2.26
750.
0355
0.05
880.
0009
0.93
8912
5823
1172
1612
0211
1155
1693
1258
Spo
t 14
0.26
0.09
450.
0010
0.25
560.
0038
3.33
090.
0491
0.06
920.
0009
0.99
7215
1819
1468
1914
8812
1352
1697
1518
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
Sam
ple
BR
Z-01
93
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 15
0.31
0.08
370.
0010
0.20
510.
0030
2.36
670.
0367
0.06
150.
0009
0.94
9412
8523
1203
1612
3311
1206
1694
1285
Spo
t 16
0.11
0.07
660.
0009
0.18
020.
0025
1.90
290.
0272
0.06
510.
0010
0.96
1911
1122
1068
1410
8210
1275
1996
1111
Spo
t 17
0.61
0.13
280.
0015
0.15
480.
0022
2.83
430.
0411
0.06
230.
0009
0.96
2121
3619
928
1213
6511
1221
1743
928
Spo
t 18
0.52
0.11
630.
0017
0.16
520.
0023
2.64
970.
0434
0.05
960.
0016
0.85
8319
0126
986
1313
1512
1171
3152
986
Spo
t 19
0.24
0.07
040.
0014
0.15
520.
0023
1.50
570.
0325
0.04
900.
0014
0.69
3894
041
930
1393
313
967
2799
930
Spo
t 20
0.42
0.08
520.
0011
0.21
640.
0035
2.54
110.
0434
0.05
370.
0009
0.93
6713
1925
1263
1812
8412
1058
1896
1319
Spo
t 21
0.32
0.08
330.
0010
0.21
090.
0031
2.42
180.
0380
0.05
830.
0009
0.94
6012
7623
1234
1712
4911
1145
1797
1276
Spo
t 22
0.26
0.07
710.
0011
0.15
580.
0024
1.65
670.
0287
0.05
190.
0012
0.88
1511
2528
933
1399
211
1022
2383
933
Spo
t 23
0.25
0.07
640.
0010
0.17
610.
0026
1.85
360.
0310
0.05
050.
0009
0.89
5811
0427
1046
1410
6511
996
1795
1104
Spo
t 24
0.30
0.06
990.
0011
0.15
040.
0021
1.45
050.
0255
0.04
360.
0009
0.80
6892
732
903
1291
011
862
1697
903
Spo
t 25
0.56
0.09
630.
0012
0.27
250.
0039
3.61
520.
0545
0.07
290.
0010
0.94
2615
5322
1553
2015
5312
1423
1810
015
53
Spo
t 28
0.35
0.07
740.
0019
0.17
040.
0028
1.81
710.
0463
0.05
260.
0016
0.64
2511
3148
1014
1510
5217
1036
3190
1131
Spo
t 29
0.25
0.07
640.
0012
0.17
470.
0027
1.84
140.
0338
0.05
090.
0011
0.83
5311
0731
1038
1510
6012
1003
2194
1107
Spo
t 31
0.23
0.08
090.
0009
0.20
050.
0029
2.23
510.
0326
0.05
770.
0008
0.97
7212
1821
1178
1511
9210
1134
1597
1218
Spo
t 33
0.31
0.08
160.
0010
0.19
760.
0029
2.22
370.
0355
0.05
820.
0010
0.91
5312
3625
1163
1611
8911
1143
1894
1236
Spo
t 34
0.44
0.09
790.
0011
0.26
320.
0039
3.54
990.
0543
0.07
400.
0010
0.96
9015
8421
1506
2015
3812
1444
1995
1584
Spo
t 37
0.39
0.09
260.
0010
0.18
200.
0026
2.32
270.
0333
0.05
540.
0007
0.97
7814
7921
1078
1412
1910
1089
1373
1479
Spo
t 38
0.32
0.07
200.
0013
0.15
730.
0023
1.56
070.
0301
0.04
810.
0010
0.77
1698
535
942
1395
512
949
2096
942
Spo
t 39
0.21
0.07
180.
0008
0.15
240.
0021
1.50
860.
0216
0.04
480.
0006
0.97
3598
022
915
1293
49
886
1193
915
Spo
t 41
0.26
0.08
1 10.
0010
0.19
420.
0028
2.17
220.
0333
0.05
750.
0008
0.94
6612
2423
1144
1511
7211
1131
1693
1224
Spo
t 42
0.40
0.08
530.
0010
0.22
440.
0031
2.63
810.
0391
0.06
830.
0010
0.92
9913
2223
1305
1613
1111
1335
1899
1322
Spo
t 43
0.37
0.07
180.
0018
0.15
040.
0025
1.48
830.
0389
0.05
140.
0014
0.62
8998
050
903
1492
616
1013
2792
903
Spo
t 44
0.40
0.08
320.
0011
0.20
720.
0029
2.37
710.
0363
0.06
370.
0009
0.90
4712
7425
1214
1512
3611
1249
1895
1274
Spo
t 47
0.49
0.07
690.
0015
0.17
370.
0027
1.84
070.
0394
0.05
280.
0012
0.72
7211
1839
1032
1510
6014
1040
2292
1118
Spo
t 50
0.37
0.07
900.
0009
0.20
150.
0028
2.19
350.
0323
0.06
040.
0008
0.93
7711
7123
1184
1511
7910
1186
1610
111
71
Spo
t 52
0.15
0.07
060.
0010
0.15
910.
0022
1.54
860.
0246
0.05
010.
0011
0.85
8994
628
952
1295
010
989
2010
195
2
Spo
t 57
0.30
0.08
610.
0010
0.22
670.
0032
2.68
970.
0397
0.06
710.
0009
0.96
1913
4021
1317
1713
2611
1312
1798
1340
Spo
t 58
0.16
0.09
760.
0015
0.20
630.
0035
2.77
450.
0519
0.09
830.
0025
0.89
4915
7828
1209
1813
4914
1895
4577
1578
Spo
t 59
0.25
0.08
170.
0010
0.18
340.
0029
2.06
620.
0341
0.05
660.
0010
0.95
8612
3923
1086
1611
3811
1114
1988
1239
Spo
t 61
0.45
0.08
800.
0015
0.22
770.
0033
2.76
170.
0509
0.07
150.
0014
0.79
0813
8232
1322
1713
4514
1396
2696
1382
Spo
t 62
0.30
0.07
060.
0011
0.15
440.
0022
1.50
270.
0270
0.04
810.
0009
0.80
6394
632
926
1393
211
949
1898
926
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
94
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 63
0.28
0.07
650.
0010
0.17
020.
0024
1.79
570.
0289
0.05
500.
0009
0.87
7111
0927
1013
1310
4410
1083
1891
1109
Spo
t 64
0.40
0.08
130.
0013
0.20
410.
0030
2.28
800.
0415
0.06
210.
0012
0.80
5712
2931
1197
1612
0913
1217
2297
1229
Spo
t 65
0.25
0.08
190.
0010
0.21
780.
0032
2.45
870.
0397
0.06
480.
0011
0.92
2612
4324
1270
1712
6012
1270
2110
212
43
Spo
t 67
0.24
0.11
280.
0012
0.26
880.
0039
4.18
100.
0611
0.07
790.
0010
0.98
3218
4519
1535
2016
7012
1517
1983
1845
Spo
t 69
0.35
0.09
440.
0015
0.26
070.
0039
3.39
380.
0603
0.07
540.
0015
0.84
1415
1729
1493
2015
0314
1469
2898
1517
Spo
t 70
0.35
0.08
050.
0010
0.19
840.
0029
2.20
200.
0353
0.05
450.
0008
0.90
6212
1025
1167
1611
8211
1073
1696
1210
Spo
t 71
0.45
0.06
230.
0020
0.10
370.
0017
0.89
060.
0284
0.03
200.
0011
0.51
3868
667
636
1064
715
636
2193
636
Spo
t 72
0.58
0.07
370.
0012
0.17
340.
0025
1.76
130.
0325
0.04
820.
0008
0.79
0210
3333
1031
1410
3112
951
1610
010
33
Spo
t 73
0.38
0.08
010.
0010
0.19
990.
0028
2.20
610.
0336
0.05
490.
0008
0.91
5811
9824
1175
1511
8311
1080
1598
1198
Spo
t 74
0.17
0.07
790.
0009
0.17
710.
0026
1.90
260.
0294
0.05
380.
0008
0.96
1811
4423
1051
1410
8210
1059
1692
1144
Spo
t 75
0.59
0.08
400.
0010
0.22
160.
0032
2.56
540.
0388
0.05
610.
0007
0.94
6112
9223
1290
1712
9111
1104
1310
012
92
Spo
t 76
0.29
0.12
190.
0013
0.36
170.
0051
6.07
870.
0872
0.09
840.
0012
0.99
0219
8419
1990
2419
8713
1898
2210
019
84
Spo
t 77
0.34
0.07
980.
0009
0.20
220.
0029
2.22
590.
0336
0.05
390.
0007
0.94
5611
9323
1187
1511
8911
1061
1410
011
93
Spo
t 80
0.26
0.07
070.
0011
0.15
490.
0023
1.51
020.
0275
0.04
500.
0009
0.80
7995
032
928
1393
511
890
1898
928
Spo
t 83
3.76
0.07
400.
0023
0.15
610.
0029
1.59
120.
0500
0.03
880.
0006
0.58
5210
4061
935
1696
720
769
1290
935
Spo
t 85
0.28
0.08
430.
0019
0.19
720.
0034
2.29
080.
0563
0.05
500.
0017
0.70
7912
9944
1160
1812
1017
1081
3289
1299
Spo
t 86
0.36
0.08
170.
0015
0.20
700.
0032
2.33
150.
0468
0.06
240.
0014
0.75
8812
3835
1213
1712
2214
1224
2698
1238
Spo
t 90
0.31
0.07
030.
0017
0.16
840.
0026
1.63
170.
0396
0.05
070.
0016
0.64
1993
748
1003
1498
315
999
3010
793
7
Spo
t 91
0.39
0.08
120.
0010
0.18
130.
0028
2.03
010.
0337
0.05
260.
0009
0.92
3412
2725
1074
1511
2611
1036
1788
1227
Spo
t 92
0.18
0.08
180.
0010
0.21
740.
0031
2.45
100.
0379
0.06
470.
0012
0.90
7712
4025
1268
1612
5811
1266
2310
212
40
Spo
t 95
0.29
0.07
140.
0010
0.15
780.
0023
1.55
380.
0261
0.04
600.
0008
0.86
2697
029
945
1395
210
910
1597
945
Spo
t 97
0.36
0.08
160.
0009
0.20
960.
0030
2.35
680.
0352
0.05
660.
0007
0.96
7712
3522
1227
1612
3011
111 2
1499
1235
Spo
t 99
0.27
0.08
030.
0009
0.20
200.
0029
2.23
720.
0338
0.05
470.
0008
0.94
9612
0523
1186
1611
9311
1075
1598
1205
Spo
t 106
0.25
0.07
290.
0009
0.17
790.
0026
1.78
870.
0287
0.04
970.
0008
0.92
1010
1225
1055
1410
4110
980
1610
410
12
Spo
t 107
0.46
0.08
000.
0014
0.21
640.
0033
2.38
570.
0458
0.06
740.
0014
0.78
7611
9633
1263
1712
3814
1318
2710
611
96
Spo
t 109
0.51
0.08
840.
0011
0.24
320.
0035
2.96
400.
0459
0.07
470.
0011
0.91
9413
9124
1403
1813
9812
1455
2010
113
91
Spo
t 110
0.33
0.09
400.
0015
0.20
310.
0032
2.63
240.
0500
0.07
950.
0016
0.83
3915
0830
1192
1713
1014
1546
3079
1508
Spo
t 113
0.79
0.08
710.
0015
0.24
920.
0040
2.99
300.
0593
0.06
640.
0012
0.81
6013
6332
1435
2114
0615
1299
2210
513
63
Spo
t 115
0.24
0.07
370.
0015
0.16
480.
0024
1.67
410.
0347
0.04
910.
0015
0.70
5810
3339
983
1399
913
970
2895
983
Spo
t 117
0.20
0.07
450.
0010
0.17
910.
0026
1.84
030.
0298
0.05
380.
0010
0.89
1010
5626
1062
1410
6011
1059
1910
110
56
Spo
t 118
0.37
0.08
200.
0010
0.20
570.
0029
2.32
710.
0364
0.06
140.
0010
0.91
1512
4624
1206
1612
2111
1205
1897
1246
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
95
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 119
0.40
0.07
440.
0014
0.17
420.
0029
1.78
760.
0384
0.04
290.
0010
0.76
9610
5338
1035
1610
4114
849
1998
1053
Spo
t 121
0.72
0.08
160.
0010
0.20
380.
0029
2.29
390.
0367
0.06
130.
0009
0.90
2012
3625
1196
1612
1011
1202
1697
1236
Spo
t 124
0.23
0.07
870.
0014
0.19
610.
0029
2.12
840.
0418
0.05
750.
0016
0.75
2611
6535
1154
1611
5814
1131
3099
1165
Spo
t 126
0.15
0.08
090.
0010
0.16
190.
0023
1.80
530.
0279
0.05
790.
0010
0.93
1512
1823
967
1310
4710
1139
1879
967
Spo
t 128
0.64
0.08
000.
0012
0.19
430.
0027
2.14
530.
0358
0.05
810.
0010
0.84
3011
9828
1145
1511
6412
1141
1996
1198
Spo
t 129
0.68
0.07
770.
0019
0.16
530.
0026
1.77
320.
0452
0.04
710.
0012
0.62
1811
4049
986
1410
3617
931
2387
986
Spo
t 131
0.36
0.07
150.
0012
0.15
130.
0022
1.49
110.
0282
0.04
630.
0010
0.77
2697
134
908
1292
711
915
1994
908
Spo
t 132
0.17
0.07
210.
0009
0.15
490.
0022
1.53
980.
0239
0.04
720.
0008
0.91
3398
825
929
1294
610
932
1694
929
Spo
t 133
0.33
0.12
460.
0013
0.10
570.
0015
1.81
650.
0265
0.05
710.
0007
0.98
0520
2419
648
910
5110
1123
1432
648
Spo
t 134
0.18
0.08
090.
0010
0.20
490.
0031
2.28
470.
0380
0.06
250.
0012
0.92
1112
1825
1202
1712
0812
1225
2399
1218
Spo
t 137
0.18
0.08
340.
0010
0.21
860.
0031
2.51
290.
0375
0.06
640.
0010
0.95
0712
7822
1275
1612
7611
1299
2010
012
78
Spo
t 140
0.21
0.08
370.
0010
0.19
620.
0028
2.26
400.
0345
0.04
970.
0009
0.92
9412
8623
1155
1512
0111
980
1790
1286
Spo
t 141
0.32
0.08
250.
0010
0.21
140.
0033
2.40
500.
0394
0.05
470.
0009
0.94
4512
5823
1236
1712
4412
1077
1798
1258
Spo
t 143
0.68
0.09
110.
0018
0.22
240.
0037
2.79
460.
0609
0.06
880.
0016
0.76
5714
4937
1295
2013
5416
1346
2989
1449
Spo
t 144
0.44
0.07
660.
0013
0.17
050.
0026
1.80
060.
0343
0.04
880.
0009
0.79
4011
1133
1015
1410
4612
962
1891
1111
Spo
t 10.
520.
0931
0.00
100.
2626
0.00
343.
3726
0.04
530.
0702
0.00
080.
9641
1490
2115
0317
1498
1113
7115
101
1490
Spo
t 20.
290.
0709
0.00
100.
1564
0.00
211.
5294
0.02
510.
0420
0.00
070.
8353
954
3093
712
942
1083
114
9893
7
Spo
t 41.
130.
1038
0.00
150.
2687
0.00
403.
8427
0.06
610.
0708
0.00
100.
8669
1692
2715
3420
1602
1413
8218
9116
92
Spo
t 50.
390.
0964
0.00
110.
2726
0.00
363.
6264
0.04
930.
0720
0.00
090.
9607
1556
2115
5418
1555
1114
0516
100
1556
Spo
t 60.
350.
0873
0.00
100.
2358
0.00
312.
8392
0.03
850.
0623
0.00
070.
9601
1367
2213
6516
1366
1012
2214
100
1367
Spo
t 70.
510.
0816
0.00
100.
2102
0.00
272.
3653
0.03
340.
0569
0.00
070.
9241
1235
2412
3015
1232
1011
1 813
100
1235
Spo
t 80.
730.
0951
0.00
100.
2656
0.00
333.
4824
0.04
450.
0315
0.00
040.
9755
1529
2015
1817
1523
1062
77
9915
29
Spo
t 90.
310.
0752
0.00
170.
1730
0.00
261.
7940
0.04
160.
0515
0.00
140.
6561
1074
4510
2914
1043
1510
1527
9610
74
Spo
t 10
0.73
0.09
290.
0011
0.25
960.
0034
3.32
730.
0460
0.06
750.
0007
0.94
7914
8622
1488
1714
8811
1321
1410
014
86
Spo
t 12
0.41
0.07
950.
0008
0.19
670.
0026
2.15
640.
0289
0.05
550.
0006
0.99
0811
8621
1158
1411
679
1091
1298
1186
Spo
t 14
0.30
0.07
430.
0010
0.17
610.
0023
1.80
340.
0266
0.04
760.
0007
0.88
9510
4926
1046
1310
4710
941
1310
010
49
Spo
t 15
0.26
0.09
570.
0010
0.26
370.
0035
3.47
830.
0470
0.07
300.
0009
0.98
3315
4220
1509
1815
2211
1424
1798
1542
Spo
t 16
0.31
0.08
750.
0009
0.23
250.
0031
2.80
490.
0373
0.06
220.
0007
0.99
6613
7220
1347
1613
5710
1219
1398
1372
Spo
t 17
0.38
0.08
670.
0011
0.23
220.
0030
2.77
520.
0402
0.06
740.
0010
0.90
0613
5324
1346
1613
4911
1319
1810
013
53
Spo
t 18
0.26
0.07
130.
0009
0.15
420.
0021
1.51
550.
0231
0.04
570.
0007
0.88
4696
626
924
1293
79
902
1496
924
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
Sam
ple
BR
Z-02
96
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 19
0.52
0.07
860.
0008
0.20
640.
0026
2.23
720.
0287
0.03
850.
0004
0.99
2211
6221
1210
1411
939
764
810
411
62
Spo
t 20
0.59
0.08
820.
0009
0.15
810.
0020
1.92
280.
0245
0.02
420.
0003
0.98
2413
8720
946
1110
899
484
668
946
Spo
t 22
0.32
0.08
010.
0011
0.19
600.
0027
2.16
290.
0333
0.05
730.
0009
0.88
3011
9926
1154
1411
6911
1126
1796
1199
Spo
t 23
0.33
0.09
560.
0010
0.27
170.
0036
3.58
350.
0476
0.07
100.
0008
0.98
6515
4120
1550
1815
4611
1386
1510
115
41
Spo
t 24
0.46
0.08
570.
0016
0.21
870.
0031
2.58
410.
0523
0.06
310.
0013
0.70
5113
3236
1275
1712
9615
1237
2496
1332
Spo
t 26
0.40
0.07
840.
0014
0.18
760.
0025
2.02
750.
0362
0.05
680.
0011
0.73
5411
5734
1108
1311
2512
1117
2296
1157
Spo
t 28
0.45
0.07
180.
0008
0.16
860.
0022
1.66
840.
0231
0.04
760.
0006
0.93
0798
024
1004
1299
79
940
1110
298
0
Spo
t 28b
0.67
0.09
830.
0016
0.27
520.
0037
3.72
780.
0646
0.07
200.
0013
0.77
7815
9231
1567
1915
7714
1404
2498
1592
Spo
t 30
1.00
0.09
670.
0011
0.20
350.
0026
2.71
250.
0353
0.01
930.
0002
0.96
7615
6121
1194
1413
3210
387
577
1561
Spo
t 32
0.17
0.07
860.
0009
0.20
290.
0026
2.19
980.
0298
0.05
890.
0009
0.93
4011
6323
1191
1411
819
1157
1810
211
63
Spo
t 33
0.45
0.09
240.
0011
0.24
860.
0031
3.16
540.
0434
0.07
240.
0010
0.91
5814
7523
1431
1614
4911
1413
1997
1475
Spo
t 35
0.24
0.07
280.
0014
0.17
070.
0023
1.71
200.
0345
0.05
130.
0015
0.67
3610
0739
1016
1310
1313
1012
2810
110
07
Spo
t 36
0.40
0.07
260.
0011
0.16
590.
0021
1.65
950.
0265
0.04
490.
0008
0.80
5510
0230
990
1299
310
888
1599
990
Spo
t 37
0.30
0.07
960.
0010
0.19
900.
0025
2.18
240.
0299
0.05
600.
0008
0.92
0411
8624
1170
1311
7510
1102
1699
1186
Spo
t 38
1.61
0.11
390.
0013
0.33
470.
0044
5.25
400.
0704
0.08
720.
0010
0.97
0318
6220
1861
2118
6111
1690
1810
018
62
Spo
t 39
0.40
0.09
830.
0012
0.28
660.
0036
3.88
410.
0526
0.08
340.
0012
0.93
8715
9222
1625
1816
1011
1620
2210
215
92
Spo
t 39r
0.17
0.09
840.
0013
0.28
310.
0036
3.83
970.
0556
0.07
750.
0018
0.88
8315
9424
1607
1816
0112
1509
3310
115
94
Spo
t 42
0.39
0.08
430.
0011
0.22
680.
0029
2.63
680.
0387
0.07
100.
0011
0.87
0613
0026
1318
1513
1111
1386
2110
113
00
Spo
t 45
0.50
0.09
420.
0011
0.26
610.
0033
3.45
370.
0451
0.08
110.
0010
0.95
5715
1121
1521
1715
1710
1575
1910
115
11
Spo
t 47
0.40
0.07
260.
0012
0.17
220.
0023
1.72
180.
0295
0.05
440.
0010
0.76
6010
0233
1024
1210
1711
1070
1910
210
02
Spo
t 49
0.30
0.07
050.
0009
0.15
430.
0020
1.49
930.
0219
0.04
900.
0008
0.87
4894
326
925
1193
09
966
1598
925
Spo
t 51
0.73
0.09
500.
0016
0.24
480.
0037
3.20
330.
0586
0.04
530.
0016
0.82
8915
2731
141 1
1914
5814
896
3092
1527
Spo
t 52
0.31
0.06
990.
0016
0.15
170.
0022
1.46
150.
0342
0.04
750.
0013
0.60
8992
546
910
1291
514
938
2698
910
Spo
t 55
0.28
0.07
820.
0010
0.19
240.
0025
2.07
270.
0306
0.05
830.
0009
0.89
0311
5125
1134
1411
4010
1145
1899
1151
Spo
t 56
0.39
0.08
740.
0010
0.23
810.
0031
2.86
770.
0382
0.07
060.
0009
0.96
3913
6921
1377
1613
7410
1378
1710
113
69
Spo
t 57
0.30
0.06
980.
0013
0.15
740.
0021
1.51
470.
0283
0.04
920.
0011
0.72
0192
336
942
1293
611
970
2110
294
2
Spo
t 60
0.23
0.07
740.
0009
0.19
620.
0025
2.09
410.
0274
0.05
120.
0007
0.96
3911
3222
1155
1311
479
1010
1410
211
32
Spo
t 61
0.32
0.09
990.
0012
0.28
760.
0038
3.96
210.
0563
0.08
580.
0013
0.92
0716
2323
1630
1916
2712
1663
2510
016
23
Spo
t 65
0.29
0.07
010.
0013
0.14
980.
0020
1.44
750.
0272
0.05
070.
0012
0.71
0193
137
900
1190
911
999
2297
900
Spo
t 69
0.37
0.09
630.
0013
0.24
690.
0035
3.27
480.
0526
0.06
020.
0013
0.89
3715
5425
1422
1814
7512
1182
2592
1554
Spo
t 70
0.28
0.08
050.
0011
0.19
690.
0027
2.18
410.
0349
0.03
970.
0008
0.87
1712
0827
1159
1511
7611
786
1696
1208
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
97
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 74
0.32
0.08
490.
0010
0.22
320.
0028
2.61
350.
0344
0.06
700.
0009
0.95
2013
1422
1299
1513
0410
1311
1899
1314
Spo
t 75
0.25
0.09
640.
0027
0.24
970.
0040
3.32
000.
0933
0.07
580.
0039
0.57
0315
5652
1437
2114
8622
1477
7392
1556
Spo
t 76
0.34
0.07
900.
0010
0.19
630.
0026
2.13
820.
0304
0.05
670.
0008
0.91
7611
7324
1155
1411
6110
1115
1699
1173
Spo
t 79
0.25
0.08
020.
0011
0.19
720.
0026
2.18
080.
0321
0.06
000.
0011
0.88
1312
0226
1160
1411
7510
1178
2097
1202
Spo
t 80
0.24
0.07
120.
0015
0.15
110.
0021
1.48
330.
0324
0.04
880.
0015
0.64
1596
343
907
1292
413
963
2894
907
Spo
t 81
0.38
0.09
070.
0012
0.24
250.
0032
3.03
090.
0461
0.06
910.
0012
0.87
1014
3925
1400
1714
1512
1351
2297
1439
Spo
t 82
0.70
0.09
370.
0012
0.25
390.
0034
3.27
840.
0484
0.07
300.
0010
0.89
4215
0124
1458
1714
7611
1423
1997
1501
Spo
t 85
0.28
0.08
050.
0010
0.19
420.
0026
2.15
470.
0312
0.05
750.
0009
0.91
3912
0924
1144
1411
6710
1131
1795
1209
Spo
t 86
0.38
0.07
250.
0012
0.15
380.
0021
1.53
590.
0269
0.04
790.
0009
0.77
5399
932
922
1294
511
946
1792
922
Spo
t 87
0.59
0.09
230.
0012
0.24
500.
0033
3.11
740.
0461
0.07
430.
0011
0.89
9814
7324
1413
1714
3711
1449
2096
1473
Spo
t 89
0.27
0.07
220.
0011
0.15
020.
0020
1.49
460.
0248
0.04
830.
0009
0.81
3599
130
902
1192
810
953
1791
902
Spo
t 93
0.29
0.09
430.
0011
0.24
830.
0033
3.22
940.
0444
0.07
440.
0011
0.95
7515
1521
1430
1714
6411
1451
2094
1515
Spo
t 94
0.22
0.08
580.
0010
0.22
580.
0030
2.67
140.
0376
0.06
250.
0010
0.95
7513
3422
1313
1613
2110
1225
1898
1334
Spo
t 95
1.29
0.09
950.
0015
0.24
550.
0033
3.36
690.
0553
0.03
130.
0007
0.80
8916
1429
1415
1714
9713
623
1388
1614
Spo
t 97
0.46
0.09
090.
0012
0.23
010.
0031
2.88
290.
0443
0.06
970.
0011
0.87
4814
4425
1335
1613
7812
1362
2092
1444
Spo
t 101
0.33
0.09
800.
0011
0.26
680.
0036
3.60
570.
0503
0.07
570.
0011
0.97
2215
8721
1525
1815
5111
1474
2096
1587
Spo
t 104
0.68
0.08
520.
0013
0.20
640.
0028
2.42
460.
0400
0.06
480.
0010
0.81
8613
2029
1210
1512
5012
1270
1992
1320
Spo
t 106
0.38
0.07
870.
0009
0.19
650.
0026
2.13
360.
0299
0.06
060.
0008
0.93
3111
6523
1157
1411
6010
1189
1699
1165
Spo
t 107
0.65
0.10
100.
0012
0.28
220.
0037
3.92
720.
0541
0.07
710.
0010
0.94
7616
4221
1602
1916
1911
1501
2098
1642
Spo
t 109
0.33
0.08
710.
0009
0.23
020.
0030
2.76
230.
0365
0.06
920.
0009
0.98
0213
6220
1335
1613
4510
1353
1798
1362
Spo
t 110
0.18
0.09
630.
0010
0.26
560.
0035
3.52
730.
0465
0.08
060.
0011
0.99
3515
5420
1518
1815
3310
1566
2198
1554
Spo
t 111
0.54
0.10
820.
0012
0.30
660.
0039
4.57
090.
0606
0.08
490.
0014
0.95
2717
6921
1724
1917
4411
1646
2697
1769
Spo
t 114
0.27
0.07
890.
0009
0.19
010.
0025
2.06
710.
0283
0.05
470.
0008
0.95
9011
6922
1122
1411
389
1076
1496
1169
Spo
t 115
0.46
0.08
640.
0010
0.22
270.
0029
2.65
270.
0359
0.06
290.
0008
0.97
1313
4821
1296
1513
1510
1232
1596
1348
Spo
t 116
0.20
0.07
490.
0009
0.16
890.
0023
1.74
410.
0247
0.04
980.
0008
0.95
4110
6623
1006
1310
259
982
1594
1066
Spo
t 118
0.47
0.08
040.
0017
0.19
460.
0031
2.15
560.
0489
0.05
320.
0017
0.69
6212
0742
1146
1711
6716
1047
3395
1207
Spo
t 119
0.34
0.08
750.
0010
0.22
500.
0030
2.71
480.
0376
0.06
460.
0009
0.95
4213
7222
1308
1613
3310
1266
1795
1372
Spo
t 120
0.34
0.08
780.
0011
0.22
390.
0030
2.70
900.
0391
0.06
390.
0010
0.92
6113
7823
1302
1613
3111
1252
1895
1378
Spo
t 121
0.51
0.10
440.
0012
0.28
940.
0038
4.16
420.
0574
0.08
030.
0011
0.95
5717
0421
1638
1916
6711
1561
2196
1704
Spo
t 122
0.42
0.08
730.
0010
0.22
180.
0029
2.66
740.
0375
0.06
210.
0008
0.94
4013
6622
1291
1613
2010
1218
1695
1366
Spo
t 123
0.16
0.09
790.
0011
0.26
790.
0035
3.61
420.
0486
0.07
880.
0012
0.98
0215
8420
1530
1815
5311
1533
2297
1584
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
98
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 125
0.54
0.07
700.
0009
0.17
610.
0023
1.86
790.
0262
0.04
940.
0006
0.94
4911
2023
1045
1310
709
974
1293
1120
Spo
t 127
0.26
0.07
210.
0011
0.15
680.
0022
1.55
770.
0268
0.04
660.
0009
0.80
1698
831
939
1295
411
920
1795
939
Spo
t 129
0.62
0.08
190.
0009
0.20
110.
0027
2.27
010.
0314
0.05
290.
0006
0.97
2912
4321
1181
1512
0310
1041
1195
1243
Spo
t 130
0.39
0.07
530.
0013
0.16
800.
0024
1.74
510.
0337
0.05
040.
0010
0.72
7210
7735
1001
1310
2512
994
1993
1077
Spo
t 134
0.67
0.11
140.
0013
0.30
710.
0042
4.71
720.
0690
0.08
200.
0010
0.93
9218
2321
1726
2117
7012
1593
1995
1823
Spo
t 136
0.22
0.07
250.
0009
0.15
320.
0021
1.53
170.
0233
0.04
470.
0007
0.89
2410
0026
919
1294
39
884
1492
919
Spo
t 137
0.57
0.09
900.
0012
0.26
550.
0037
3.62
440.
0528
0.07
010.
0009
0.94
3216
0622
1518
1915
5512
1369
1695
1606
Spo
t 138
0.27
0.07
520.
0009
0.16
820.
0023
1.74
360.
0265
0.04
530.
0007
0.90
6510
7425
1002
1310
2510
896
1393
1074
Spo
t 139
0.41
0.07
780.
0014
0.17
340.
0025
1.86
060.
0368
0.04
760.
0010
0.72
0611
4236
1031
1410
6713
940
1990
1142
Spo
t 10.
380.
1028
0.00
120.
2698
0.00
353.
8217
0.05
280.
0803
0.00
110.
9356
1675
2115
4018
1597
1115
6120
9216
75
Spo
t 30.
290.
0954
0.00
100.
2754
0.00
403.
6245
0.05
360.
0793
0.00
120.
9895
1537
2015
6820
1555
1215
4323
102
1537
Spo
t 40.
420.
0974
0.00
120.
2852
0.00
373.
8273
0.05
520.
0781
0.00
120.
8896
1574
2316
1718
1599
1215
2022
103
1574
Spo
t 50.
410.
0806
0.00
160.
1978
0.00
272.
1975
0.04
560.
0580
0.00
140.
6649
1211
3911
6315
1180
1411
3926
9612
11
Spo
t 60.
390.
0965
0.00
120.
2801
0.00
363.
7278
0.05
350.
0832
0.00
130.
8927
1558
2315
9218
1577
1216
1524
102
1558
Spo
t 70.
390.
0936
0.00
110.
2478
0.00
333.
1972
0.04
690.
0702
0.00
110.
9200
1501
2314
2717
1457
1113
7020
9515
01
Spo
t 80.
700.
0967
0.00
140.
2736
0.00
363.
6454
0.05
930.
0782
0.00
120.
8137
1561
2815
5918
1560
1315
2323
100
1561
Spo
t 90.
460.
0956
0.00
130.
2719
0.00
363.
5848
0.05
510.
0754
0.00
120.
8588
1541
2515
5118
1546
1214
7023
101
1541
Spo
t 10
0.48
0.10
200.
0013
0.28
360.
0037
3.98
930.
0582
0.08
260.
0013
0.88
2416
6224
1609
1816
3212
1605
2497
1662
Spo
t 14
0.50
0.10
850.
0012
0.29
060.
0042
4.34
800.
0638
0.08
340.
0013
0.98
1117
7520
1644
2117
0312
1619
2493
1775
Spo
t 16
0.46
0.07
960.
0014
0.19
690.
0027
2.16
040.
0403
0.05
960.
0012
0.73
491 1
8634
1159
1511
6813
1170
2398
1186
Spo
t 18
0.37
0.07
250.
0013
0.15
760.
0022
1.57
460.
0304
0.04
800.
0011
0.70
9999
937
943
1296
012
947
2094
943
Spo
t 19
0.30
0.08
980.
0012
0.16
780.
0022
2.07
850.
0303
0.05
610.
0009
0.88
4514
2224
1000
1211
4210
1102
1870
1000
Spo
t 21
0.19
0.09
900.
0016
0.27
260.
0036
3.72
150.
0627
0.07
760.
0022
0.79
3216
0629
1554
1815
7613
1510
4197
1606
Spo
t 22
0.20
0.07
660.
0015
0.20
250.
0029
2.13
820.
0441
0.05
880.
0019
0.68
9811
1139
1189
1511
6114
1156
3610
711
11
Spo
t 23
0.37
0.07
540.
0008
0.19
050.
0027
1.97
970.
0286
0.05
840.
0008
0.97
6910
7922
1124
1511
0910
1148
1510
410
79
Spo
t 24
0.66
0.08
780.
0013
0.23
050.
0030
2.78
840.
0461
0.06
560.
0011
0.79
7613
7729
1337
1613
5212
1284
2197
1377
Spo
t 25
0.31
0.11
350.
0012
0.21
360.
0031
3.34
220.
0488
0.07
170.
0011
0.98
4418
5619
1248
1614
9111
1400
2067
1856
Spo
t 26
0.45
0.09
490.
0018
0.28
010.
0043
3.66
400.
0728
0.06
970.
0034
0.77
9515
2734
1592
2215
6416
1361
6510
415
27
Spo
t 27
0.50
0.08
710.
0013
0.24
220.
0038
2.90
950.
0522
0.07
430.
0015
0.86
5513
6328
1398
2013
8414
1449
2810
313
63
Spo
t 28
0.27
0.09
720.
0010
0.27
680.
0039
3.70
920.
0519
0.07
210.
0010
0.99
7015
7119
1575
2015
7311
1407
1910
015
71
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
Sam
ple
BR
Z-15
99
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 29
0.71
0.09
880.
0011
0.28
210.
0041
3.84
500.
0569
0.08
650.
0012
0.96
9816
0221
1602
2016
0212
1676
2310
016
02
Spo
t 30
0.43
0.08
500.
0013
0.22
660.
0030
2.65
400.
0428
0.06
450.
0012
0.81
6413
1528
1316
1613
1612
1263
2310
013
15
Spo
t 31
0.38
0.10
500.
0013
0.25
120.
0041
3.63
350.
0609
0.08
170.
0037
0.97
1917
1422
1444
2115
5713
1588
6984
1714
Spo
t 34
0.40
0.10
580.
0012
0.30
390.
0046
4.43
230.
0702
0.07
680.
0016
0.96
0017
2821
1710
2317
1813
1495
2999
1728
Spo
t 37
0.36
0.09
320.
0014
0.26
180.
0035
3.36
250.
0552
0.07
640.
0016
0.80
7814
9228
1499
1814
9613
1488
3010
114
92
Spo
t 38
0.30
0.07
950.
0013
0.19
870.
0027
2.17
700.
0384
0.05
910.
0014
0.75
5611
8432
1169
1411
7412
1161
2699
1184
Spo
t 39
0.58
0.11
110.
0013
0.29
730.
0047
4.55
630.
0739
0.08
540.
0023
0.96
4118
1821
1678
2317
4114
1657
4392
1818
Spo
t 40
0.66
0.09
160.
0014
0.24
910.
0033
3.14
360.
0520
0.07
200.
0013
0.79
9214
5829
1434
1714
4313
1406
2498
1458
Spo
t 41
0.27
0.07
860.
0009
0.20
340.
0029
2.20
460.
0327
0.06
490.
0010
0.96
4411
6222
1194
1611
8310
1272
1910
311
62
Spo
t 43
0.46
0.09
910.
0012
0.25
060.
0040
3.42
460.
0571
0.06
350.
0020
0.94
8416
0823
1442
2015
1013
1244
3790
1608
Spo
t 47
0.18
0.07
770.
0010
0.20
070.
0026
2.14
950.
0321
0.05
680.
0012
0.86
1711
4026
1179
1411
6510
1117
2310
311
40
Spo
t 48
0.43
0.10
830.
0013
0.29
420.
0037
4.39
280.
0600
0.07
650.
0013
0.92
0617
7122
1663
1817
1111
1489
2494
1771
Spo
t 53
0.86
0.09
840.
0019
0.25
550.
0038
3.46
430.
0697
0.07
050.
0018
0.74
3015
9435
1467
2015
1916
1378
3392
1594
Spo
t 55
0.27
0.09
730.
0011
0.27
190.
0036
3.64
550.
0509
0.07
580.
0013
0.93
7815
7321
1550
1815
6011
1477
2599
1573
Spo
t 60
0.49
0.09
390.
0015
0.24
560.
0033
3.17
800.
0537
0.06
710.
0013
0.80
0215
0629
1416
1714
5213
1313
2594
1506
Spo
t 63
0.36
0.07
640.
0016
0.17
370.
0027
1.82
890.
0407
0.05
200.
0013
0.68
5011
0542
1032
1510
5615
1025
2493
1105
Spo
t 65
0.40
0.09
540.
0011
0.27
080.
0036
3.55
950.
0497
0.07
510.
0009
0.96
2415
3521
1545
1815
4111
1463
1710
115
35
Spo
t 66
0.62
0.08
780.
0012
0.24
280.
0033
2.93
790.
0457
0.06
840.
0009
0.88
1413
7725
1401
1713
9212
1337
1710
213
77
Spo
t 67
0.28
0.07
350.
0011
0.17
210.
0024
1.74
440.
0296
0.05
060.
0009
0.81
9910
2830
1024
1310
2511
999
1810
010
28
Spo
t 68
0.32
0.09
790.
0011
0.27
190.
0036
3.67
050.
0500
0.07
940.
0009
0.98
2715
8520
1550
1815
6511
1544
1798
1585
Spo
t 69
0.11
0.08
900.
0010
0.16
190.
0022
1.98
500.
0286
0.09
050.
0013
0.96
0914
0321
967
1211
1010
1750
2369
967
Spo
t 77
0.41
0.10
720.
0011
0.30
270.
0041
4.47
260.
0609
0.08
190.
0009
0.98
4717
5219
1705
2017
2611
1591
1897
1752
Spo
t 79
0.31
0.09
230.
0011
0.25
350.
0035
3.22
340.
0471
0.07
710.
0011
0.94
9714
7222
1456
1814
6311
1502
2099
1472
Spo
t 81
0.33
0.07
950.
0011
0.20
260.
0029
2.22
040.
0352
0.05
740.
0009
0.89
0811
8526
1189
1511
8811
1128
1710
011
85
Spo
t 82
0.87
0.09
730.
0017
0.26
230.
0039
3.51
750.
0670
0.07
570.
0013
0.78
1315
7333
1501
2015
3115
1475
2495
1573
Spo
t 86
0.21
0.09
380.
0011
0.26
270.
0036
3.39
670.
0493
0.07
770.
0012
0.95
5415
0422
1503
1915
0411
1512
2210
015
04
Spo
t 92
0.35
0.09
760.
0010
0.24
150.
0033
3.25
010.
0445
0.06
530.
0008
0.99
7415
7919
1394
1714
6911
1278
1488
1579
Spo
t 95
0.39
0.08
600.
0011
0.22
930.
0031
2.71
750.
0402
0.06
820.
0010
0.92
5413
3823
1331
1613
3311
1334
1899
1338
Spo
t 96
0.24
0.07
980.
0013
0.19
500.
0028
2.14
580.
0386
0.05
660.
0013
0.79
4611
9332
1148
1511
6412
1113
2596
1193
Spo
t 100
0.42
0.09
990.
0011
0.28
420.
0039
3.91
430.
0556
0.07
770.
0010
0.95
9616
2221
1612
1916
1711
1513
1999
1622
Spo
t 101
0.71
0.09
560.
0010
0.25
230.
0034
3.32
520.
0457
0.07
450.
0009
0.98
1815
4020
1450
1814
8711
1452
1694
1540
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
100
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 104
0.41
0.09
150.
0011
0.24
920.
0034
3.14
380.
0453
0.07
110.
0009
0.94
9114
5722
1435
1814
4411
1388
1898
1457
Spo
t 108
0.17
0.07
060.
0007
0.15
510.
0021
1.50
880.
0207
0.04
690.
0006
0.98
0894
521
929
1293
48
927
1198
929
Spo
t 109
0.41
0.07
860.
0016
0.17
720.
0027
1.91
980.
0416
0.05
380.
0013
0.71
3611
6240
1052
1510
8814
1058
2491
1162
Spo
t 112
0.23
0.09
720.
0010
0.26
460.
0036
3.54
550.
0486
0.07
750.
0010
0.98
6915
7119
1513
1815
3711
1509
1896
1571
Spo
t 117
0.50
0.10
370.
0011
0.25
190.
0034
3.60
080.
0492
0.06
520.
0008
0.98
9916
9119
1448
1815
5011
1277
1586
1691
Spo
t 118
0.69
0.23
450.
0025
0.60
890.
0087
19.6
862
0.28
160.
1173
0.00
160.
9966
3083
1730
6635
3076
1422
4329
9930
83
Spo
t 119
0.54
0.10
450.
0011
0.29
930.
0041
4.31
410.
0595
0.06
890.
0008
0.98
7817
0619
1688
2016
9611
1348
1599
1706
Spo
t 120
0.52
0.08
470.
0012
0.21
530.
0030
2.51
350.
0407
0.06
320.
0010
0.86
8913
0827
1257
1612
7612
1239
1896
1308
Spo
t 121
0.44
0.09
700.
0011
0.27
040.
0038
3.61
530.
0526
0.06
290.
0009
0.95
6515
6721
1543
1915
5312
1234
1698
1567
Spo
t 127
0.63
0.08
730.
0010
0.23
700.
0033
2.85
120.
0411
0.06
800.
0008
0.95
3513
6622
1371
1713
6911
1329
1610
013
66
Spo
t 128
0.33
0.09
520.
0011
0.26
560.
0037
3.48
680.
0514
0.06
490.
0010
0.94
7815
3222
1519
1915
2412
1272
1899
1532
Spo
t 129
0.29
0.10
030.
0012
0.27
350.
0043
3.77
640.
0617
0.06
270.
0026
0.96
2716
2923
1558
2215
8813
1230
5096
1629
Spo
t 130
0.35
0.09
800.
0011
0.28
730.
0040
3.88
050.
0552
0.08
010.
0011
0.96
6215
8621
1628
2016
1011
1557
2010
315
86
Spo
t 131
0.56
0.08
180.
0013
0.20
260.
0031
2.28
370.
0421
0.05
550.
0010
0.81
6312
4032
1189
1612
0713
1092
1896
1240
Spo
t 133
0.39
0.07
960.
0010
0.19
970.
0028
2.19
210.
0340
0.05
780.
0008
0.90
3211
8725
1174
1511
7911
1135
1699
1187
Spo
t 135
0.33
0.07
400.
0015
0.15
730.
0023
1.60
520.
0346
0.04
660.
0012
0.69
1110
4241
942
1397
213
921
2390
942
Spo
t 139
0.55
0.08
030.
0011
0.21
250.
0030
2.35
160.
0368
0.05
990.
0008
0.89
2812
0326
1242
1612
2811
1176
1610
312
03
Spo
t 140
0.52
0.08
740.
0012
0.22
260.
0032
2.68
130.
0430
0.06
740.
0010
0.88
8313
6926
1296
1713
2312
1318
1995
1369
Spo
t 142
0.40
0.09
630.
0012
0.27
110.
0039
3.59
760.
0549
0.07
810.
0012
0.93
1315
5323
1546
2015
4912
1520
2210
015
53
Spo
t 147
0.64
0.09
580.
0012
0.26
950.
0038
3.55
870.
0542
0.07
430.
0010
0.92
4315
4423
1538
1915
4012
1448
1910
015
44
Spo
t 152
0.24
0.1 1
630.
0012
0.20
150.
0029
3.23
040.
0464
0.08
530.
0011
0.98
8719
0019
1184
1514
6511
1654
2162
1900
Spo
t 154
0.45
0.10
510.
0013
0.29
640.
0042
4.29
280.
0657
0.08
050.
0013
0.91
8917
1523
1674
2116
9213
1565
2498
1715
Spo
t 155
0.28
0.08
590.
0009
0.14
140.
0019
1.67
460.
0230
0.04
040.
0005
0.99
9013
3620
853
1199
99
801
1064
853
Spo
t 158
0.35
0.09
490.
0011
0.26
740.
0038
3.49
760.
0525
0.07
590.
0011
0.93
8415
2522
1528
1915
2712
1478
2110
015
25
Spo
t 162
0.28
0.09
470.
0011
0.26
570.
0037
3.46
980.
0502
0.07
660.
0011
0.96
8615
2321
1519
1915
2011
1491
2010
015
23
Spo
t 164
0.49
0.09
810.
0013
0.25
020.
0036
3.38
380.
0532
0.07
240.
0011
0.90
8315
8924
1439
1815
0112
1413
2191
1589
Spo
t 166
0.73
0.09
720.
0015
0.27
140.
0042
3.63
870.
0664
0.07
780.
0014
0.83
9615
7229
1548
2115
5815
1514
2598
1572
Spo
t 167
0.64
0.08
820.
0011
0.15
270.
0022
1.85
650.
0282
0.04
810.
0007
0.93
5413
8723
916
1210
6610
949
1266
916
Spo
t 168
0.53
0.09
520.
0010
0.27
580.
0039
3.62
050.
0520
0.08
220.
0011
0.97
7315
3320
1570
2015
5411
1596
2010
215
33
Spo
t 20.
300.
0732
0.00
090.
1725
0.00
241.
7413
0.02
580.
0499
0.00
070.
9325
1020
2410
2613
1024
1098
414
101
1020
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
Sam
ple
BR
Z-24
101
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 30.
530.
0963
0.00
120.
2714
0.00
383.
6036
0.05
470.
0757
0.00
100.
9307
1554
2315
4819
1550
1214
7520
100
1554
Spo
t 40.
390.
0729
0.00
100.
1745
0.00
241.
7524
0.02
740.
0515
0.00
080.
8894
1010
2610
3713
1028
1010
1515
103
1010
Spo
t 50.
500.
0903
0.00
120.
2473
0.00
353.
0775
0.04
820.
0678
0.00
100.
8898
1431
2514
2518
1427
1213
2619
100
1431
Spo
t 60.
310.
0829
0.00
100.
2171
0.00
302.
4823
0.03
630.
0619
0.00
090.
9426
1268
2312
6716
1267
1112
1416
100
1268
Spo
t 70.
540.
0795
0.00
090.
2034
0.00
292.
2291
0.03
320.
0546
0.00
070.
9486
1185
2311
9415
1190
1010
7413
101
1185
Spo
t 90.
220.
0709
0.00
140.
1530
0.00
221.
4955
0.03
170.
0464
0.00
140.
6855
954
4191
812
929
1391
727
9691
8
Spo
t 10
0.28
0.08
680.
0010
0.23
100.
0032
2.76
210.
0401
0.06
710.
0009
0.95
5613
5522
1340
1713
4511
1313
1899
1355
Spo
t 11
0.28
0.07
340.
0009
0.17
500.
0024
1.77
080.
0260
0.04
960.
0007
0.94
0010
2524
1039
1310
3510
979
1310
110
25
Spo
t 12
0.26
0.09
610.
0010
0.27
450.
0038
3.63
560.
0503
0.07
080.
0008
0.98
9515
4919
1563
1915
5711
1383
1510
115
49
Spo
t 14
0.28
0.09
660.
0011
0.27
520.
0039
3.66
530.
0529
0.07
200.
0009
0.98
7515
6021
1567
2015
6412
1405
1710
015
60
Spo
t 15
0.35
0.09
640.
0010
0.27
430.
0038
3.64
330.
0507
0.07
550.
0009
0.98
7215
5520
1562
1915
5911
1471
1710
015
55
Spo
t 18
0.16
0.07
890.
0009
0.20
910.
0029
2.27
450.
0339
0.06
080.
0011
0.93
9811
7023
1224
1612
0411
1192
2010
511
70
Spo
t 20
0.37
0.07
310.
0013
0.17
090.
0025
1.72
220.
0324
0.05
020.
0010
0.76
7610
1734
1017
1410
1712
989
1910
010
17
Spo
t 22
0.59
0.06
040.
0018
0.10
000.
0016
0.83
350.
0254
0.03
100.
0008
0.52
1262
064
615
961
614
617
1699
615
Spo
t 23
0.29
0.06
940.
0008
0.15
560.
0021
1.48
760.
0220
0.04
550.
0007
0.92
8691
025
932
1292
59
899
1310
293
2
Spo
t 24
1.11
0.07
050.
0012
0.15
860.
0023
1.54
230.
0283
0.04
680.
0007
0.78
3294
334
949
1394
711
925
1210
194
9
Spo
t 25
0.35
0.09
480.
0010
0.26
930.
0037
3.52
030.
0481
0.07
020.
0008
0.99
4815
2419
1537
1915
3211
1371
1510
115
24
Spo
t 27
0.25
0.07
860.
0010
0.20
030.
0028
2.16
910.
0324
0.05
290.
0008
0.93
821 1
6124
1177
1511
7110
1041
1510
111
61
Spo
t 28
0.74
0.07
040.
0010
0.15
600.
0022
1.51
350.
0247
0.04
120.
0005
0.87
9194
028
934
1293
610
816
1099
934
Spo
t 29
0.16
0.08
990.
0011
0.24
930.
0035
3.09
040.
0467
0.07
550.
0014
0.93
3414
2323
1435
1814
3012
1470
2510
114
23
Spo
t 30
0.48
0.09
540.
0011
0.26
920.
0039
3.53
860.
0532
0.06
900.
0009
0.95
3215
3522
1537
2015
3612
1348
1710
015
35
Spo
t 33
0.69
0.09
610.
0012
0.27
170.
0039
3.59
720.
0547
0.06
950.
0009
0.93
3715
4923
1549
2015
4912
1358
1710
015
49
Spo
t 34
0.47
0.06
280.
0010
0.12
110.
0017
1.04
820.
0182
0.03
460.
0006
0.81
4670
132
737
1072
89
687
1110
573
7
Spo
t 36
0.31
0.09
490.
0012
0.27
230.
0039
3.56
330.
0547
0.07
300.
0012
0.92
7615
2623
1553
2015
4112
1424
2310
215
26
Spo
t 37
0.34
0.08
090.
0010
0.20
680.
0028
2.30
640.
0338
0.05
810.
0008
0.92
8512
1924
1212
1512
1410
1142
1699
1219
Spo
t 38
0.65
0.10
800.
0013
0.31
590.
0046
4.70
440.
0716
0.07
790.
0011
0.95
0417
6722
1770
2217
6813
1516
2010
017
67
Spo
t 39
0.52
0.09
480.
0010
0.27
290.
0039
3.56
510.
0509
0.06
520.
0007
0.99
8615
2420
1555
2015
4211
1276
1410
215
24
Spo
t 41
0.32
0.07
270.
0010
0.16
990.
0024
1.70
190.
0275
0.04
450.
0007
0.88
5610
0427
1012
1310
0910
880
1410
110
04
Spo
t 42
0.35
0.07
830.
0009
0.20
360.
0028
2.19
840.
0317
0.05
510.
0007
0.96
1711
5522
1194
1511
8110
1084
1410
311
55
Spo
t 43
0.62
0.08
910.
0012
0.24
680.
0035
3.03
040.
0481
0.06
600.
0010
0.88
9114
0526
1422
1814
1512
1292
1910
114
05
Spo
t 45
0.38
0.08
200.
0014
0.20
280.
0030
2.29
290.
0430
0.05
880.
0012
0.77
5112
4633
1190
1612
1013
1156
2495
1246
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
102
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 46
0.30
0.08
050.
0010
0.19
880.
0028
2.20
530.
0339
0.05
810.
0009
0.91
2512
0925
1169
1511
8311
1142
1797
1209
Spo
t 47
0.61
0.08
580.
0010
0.22
830.
0032
2.70
050.
0392
0.06
700.
0008
0.95
1713
3422
1325
1713
2911
1310
1699
1334
Spo
t 48
0.86
0.10
940.
0012
0.31
260.
0043
4.71
470.
0663
0.08
820.
0011
0.96
8617
8920
1754
2117
7012
1708
2098
1789
Spo
t 49
0.54
0.06
960.
0012
0.15
730.
0023
1.50
990.
0291
0.04
470.
0008
0.75
2291
836
942
1393
412
884
1610
394
2
Spo
t 52
0.42
0.07
150.
0014
0.16
770.
0024
1.65
270.
0341
0.04
960.
0011
0.70
3497
239
999
1399
113
979
2210
399
9
Spo
t 53
0.61
0.08
020.
0012
0.19
460.
0028
2.15
190.
0372
0.05
930.
0010
0.84
4212
0329
1146
1511
6612
1165
1895
1203
Spo
t 55
0.34
0.09
550.
0010
0.26
450.
0037
3.48
340.
0486
0.07
580.
0010
0.98
8615
3820
1513
1915
2411
1476
1898
1538
Spo
t 56
0.25
0.08
270.
0011
0.20
710.
0029
2.36
140.
0361
0.06
060.
0010
0.91
4012
6224
1213
1512
3111
1190
2096
1262
Spo
t 58
0.49
0.08
060.
0012
0.19
880.
0028
2.20
910.
0364
0.05
830.
0009
0.85
8012
1228
1169
1511
8412
1146
1896
1212
Spo
t 59
0.35
0.07
970.
0011
0.19
530.
0028
2.14
550.
0339
0.05
950.
0010
0.89
1311
8926
1150
1511
6411
1169
1897
1189
Spo
t 62
0.30
0.08
370.
0013
0.21
580.
0031
2.48
980.
0430
0.06
640.
0013
0.82
8912
8530
1260
1612
6913
1299
2598
1285
Spo
t 63
0.42
0.08
330.
0011
0.20
880.
0029
2.39
680.
0380
0.06
320.
0010
0.88
6212
7626
1222
1612
4211
1239
1996
1276
Spo
t 67
0.25
0.07
470.
0009
0.16
250.
0023
1.67
380.
0246
0.05
000.
0007
0.94
8710
6023
971
1399
99
986
1492
971
Spo
t 69
0.28
0.07
300.
0010
0.16
890.
0024
1.69
870.
0276
0.05
090.
0009
0.86
6610
1328
1006
1310
0810
1003
1799
1013
Spo
t 71
0.46
0.10
590.
0012
0.30
840.
0042
4.50
290.
0630
0.08
930.
0012
0.96
9517
3020
1733
2117
3212
1729
2210
017
30
Spo
t 73
0.83
0.08
660.
0011
0.22
360.
0031
2.66
840.
0412
0.06
640.
0009
0.90
6213
5125
1301
1613
2011
1299
1896
1351
Spo
t 75
0.27
0.07
370.
0009
0.16
850.
0024
1.71
240.
0259
0.05
100.
0008
0.92
3810
3424
1004
1310
1310
1005
1597
1034
Spo
t 78
0.46
0.10
800.
0012
0.32
200.
0045
4.79
530.
0694
0.08
720.
0012
0.96
9417
6621
1800
2217
8412
1689
2210
217
66
Spo
t 79
0.31
0.08
000.
0011
0.19
930.
0028
2.19
860.
0349
0.05
810.
0010
0.88
6111
9826
1172
1511
8111
1142
1998
1198
Spo
t 82
0.23
0.08
650.
0009
0.24
400.
0033
2.91
080.
0401
0.06
740.
0009
0.99
0113
5020
1408
1713
8510
1317
1710
413
50
Spo
t 83
0.48
0.10
840.
0012
0.32
010.
0044
4.78
170.
0673
0.08
520.
001 1
0.98
2917
7220
1790
2217
8212
1653
2010
117
72
Spo
t 84
0.42
0.08
200.
0010
0.21
150.
0030
2.39
110.
0355
0.05
460.
0007
0.94
8012
4523
1237
1612
4011
1074
1499
1245
Spo
t 86
0.41
0.09
080.
0012
0.24
920.
0036
3.11
870.
0485
0.06
410.
0010
0.91
8014
4224
1434
1814
3712
1256
1899
1442
Spo
t 88
0.26
0.07
240.
0008
0.16
460.
0023
1.64
220.
0240
0.04
290.
0006
0.96
4399
723
982
1398
79
850
1198
982
Spo
t 90
0.91
0.11
980.
0017
0.33
040.
0051
5.45
480.
0923
0.07
750.
0012
0.90
6419
5325
1840
2518
9415
1508
2394
1953
Spo
t 91
0.32
0.08
730.
0010
0.22
940.
0033
2.76
190.
0410
0.05
830.
0008
0.95
6313
6822
1332
1713
4511
1145
1597
1368
Spo
t 93
0.11
0.07
690.
0009
0.16
550.
0025
1.75
300.
0274
0.04
950.
0009
0.97
1411
1823
987
1410
2810
977
1788
987
Spo
t 96
0.27
0.07
160.
0010
0.15
860.
0023
1.56
540.
0262
0.04
210.
0007
0.86
4697
529
949
1395
710
833
1497
949
Spo
t 97
0.84
0.10
930.
0013
0.31
650.
0047
4.76
700.
0730
0.08
020.
0010
0.96
5017
8721
1773
2317
7913
1560
1999
1787
Spo
t 99
0.24
0.09
350.
0010
0.25
790.
0036
3.32
410.
0472
0.06
760.
0009
0.98
8714
9820
1479
1914
8711
1323
1699
1498
Spo
t 100
0.67
0.20
350.
0026
0.54
960.
0087
15.4
177
0.24
560.
1016
0.00
200.
9881
2854
2028
2436
2841
1519
5636
9928
54
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
103
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 104
0.26
0.08
210.
0010
0.22
700.
0033
2.56
930.
0386
0.05
960.
0009
0.95
8712
4823
1319
1712
9211
1170
1610
612
48
Spo
t 110
0.25
0.08
210.
0010
0.20
580.
0030
2.32
750.
0361
0.05
440.
0008
0.94
0312
4724
1206
1612
2111
1071
1697
1247
Spo
t 113
0.57
0.08
970.
0011
0.24
350.
0035
3.01
120.
0468
0.06
480.
0009
0.91
9914
1924
1405
1814
1112
1269
1799
1419
Spo
t 116
0.23
0.08
210.
0010
0.21
580.
0032
2.44
290.
0375
0.05
360.
0009
0.96
5012
4822
1260
1712
5511
1056
1710
112
48
Spo
t 121
0.27
0.08
180.
0009
0.20
530.
0029
2.31
480.
0342
0.05
720.
0008
0.96
0512
4022
1204
1612
1710
1124
1597
1240
Spo
t 125
1.71
0.10
940.
0016
0.31
400.
0046
4.73
410.
0794
0.08
300.
0012
0.86
4117
8926
1760
2217
7314
1611
2298
1789
Spo
t 126
0.33
0.09
140.
0012
0.24
830.
0038
3.12
860.
0524
0.04
850.
0010
0.91
6814
5426
1430
2014
4013
957
1998
1454
Spo
t 127
0.23
0.07
280.
0009
0.16
930.
0024
1.69
870.
0258
0.04
980.
0007
0.94
8310
0824
1008
1310
0810
982
1410
010
08
Spo
t 130
0.50
0.07
260.
0016
0.16
220.
0025
1.62
450.
0377
0.05
200.
0012
0.66
6510
0445
969
1498
015
1025
2397
969
Spo
t 131
0.75
0.11
740.
0014
0.34
660.
0050
5.60
790.
0840
0.09
630.
0012
0.96
5019
1621
1918
2419
1713
1858
2310
019
16
Spo
t 132
0.38
0.08
760.
0010
0.23
220.
0033
2.80
320.
0416
0.06
760.
0009
0.95
8513
7322
1346
1713
5611
1322
1798
1373
Spo
t 133
0.07
0.08
130.
0009
0.17
840.
0026
2.00
060.
0290
0.08
250.
0012
0.99
3612
3021
1058
1411
1610
1603
2286
1230
Spo
t 135
0.29
0.07
240.
0009
0.16
380.
0023
1.63
500.
0249
0.04
790.
0007
0.93
4099
724
978
1398
410
945
1498
978
Spo
t 137
0.41
0.07
390.
0012
0.16
740.
0024
1.70
420.
0310
0.04
740.
0009
0.79
5710
3833
998
1310
1012
936
1796
998
Spo
t 142
0.59
0.07
990.
0011
0.19
730.
0029
2.17
140.
0358
0.05
600.
0008
0.90
3311
9326
1161
1611
7211
1101
1697
1193
Spo
t 143
0.45
0.07
060.
0010
0.15
850.
0023
1.54
230.
0257
0.04
630.
0007
0.85
0894
629
948
1394
710
915
1410
094
8
Spo
t 146
0.35
0.07
770.
0010
0.19
630.
0028
2.10
280.
0328
0.05
690.
0009
0.90
821 1
4025
1155
1511
5011
1119
1710
111
40
Spo
t 150
0.30
0.07
290.
0012
0.16
850.
0025
1.69
300.
0317
0.04
570.
0010
0.78
0510
1034
1004
1410
0612
902
1999
1010
Spo
t 151
0.38
0.08
250.
0009
0.21
160.
0030
2.40
670.
0341
0.05
980.
0007
0.99
0712
5820
1237
1612
4510
1175
1498
1258
Spo
t 153
0.56
0.07
600.
0010
0.18
690.
0027
1.95
870.
0309
0.05
030.
0007
0.90
7310
9626
1104
1411
0111
993
1310
110
96
Spo
t 154
0.36
0.07
870.
0009
0.20
190.
0028
2.18
990.
0319
0.05
480.
0007
0.96
7411
6422
1185
1511
7810
1078
1410
211
64
Spo
t 155
0.29
0.07
940.
0009
0.19
670.
0028
2.15
240.
0314
0.05
280.
0007
0.96
8911
8222
1157
1511
6610
1040
1398
1182
Spo
t 157
0.23
0.08
130.
0010
0.20
810.
0029
2.33
310.
0346
0.05
940.
0009
0.93
7712
2923
1219
1512
2211
1166
1899
1229
Spo
t 158
0.58
0.07
300.
0014
0.16
870.
0025
1.69
850.
0337
0.04
790.
0009
0.73
8510
1537
1005
1410
0813
945
1799
1015
Spo
t 159
0.59
0.10
950.
0012
0.31
660.
0044
4.77
880.
0688
0.08
680.
0011
0.96
9217
9120
1773
2217
8112
1683
2199
1791
Spo
t 160
0.53
0.08
870.
0011
0.23
250.
0033
2.84
410.
0423
0.06
670.
0009
0.94
2113
9923
1347
1713
6711
1304
1796
1399
Spo
t 161
0.43
0.07
300.
0009
0.16
610.
0023
1.67
210.
0254
0.04
840.
0007
0.91
2010
1425
991
1399
810
955
1398
991
Spo
t 162
0.50
0.09
180.
0011
0.24
910.
0035
3.15
340.
0458
0.07
080.
0009
0.95
8414
6322
1434
1814
4611
1382
1798
1463
Spo
t 164
0.18
0.08
430.
0011
0.21
920.
0031
2.54
890.
0393
0.06
320.
0012
0.91
7213
0024
1278
1612
8611
1238
2298
1300
Spo
t 165
0.23
0.07
110.
0011
0.15
720.
0023
1.54
150.
0276
0.04
860.
0010
0.80
6096
132
941
1394
711
959
2098
941
Spo
t 166
0.51
0.09
130.
0013
0.24
800.
0036
3.12
230.
0507
0.07
090.
0011
0.88
2314
5326
1428
1814
3812
1384
2198
1453
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
104
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 1.
(con
tinue
d)
Ana
lysi
sTh
/U20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Rho
b20
7 Pb/
206 P
b±
1σ20
6 Pb/
238 U
± 1σ
207 P
b/23
5 U±
1σ20
8 Pb/
232 Th
± 1σ
Con
c.c
Spo
t 167
0.24
0.10
270.
0011
0.29
080.
0040
4.11
730.
0574
0.08
490.
0011
0.99
2016
7419
1645
2016
5811
1647
2098
1674
Spo
t 168
0.46
0.08
220.
0010
0.21
200.
0030
2.40
100.
0358
0.06
160.
0008
0.94
0612
4923
1239
1612
4311
1209
1599
1249
Spo
t 169
0.30
0.08
600.
0011
0.22
590.
0031
2.67
790.
0403
0.06
420.
0010
0.92
0513
3824
1313
1613
2211
1257
1998
1338
Spo
t 170
0.41
0.07
910.
0011
0.19
220.
0028
2.09
720.
0353
0.05
430.
0009
0.86
4411
7628
1133
1511
4812
1068
1796
1176
Spo
t 172
0.53
0.09
610.
0011
0.26
250.
0038
3.47
650.
0511
0.07
250.
0009
0.97
1215
4921
1503
1915
2212
1414
1797
1549
a Dis
play
ed ra
tios
and
ages
are
unc
orre
cted
for c
omm
on P
b.b E
rror
cor
rela
tion;
def
ined
as
[(err.
206 P
b/23
8 U)/(
mea
sure
d 20
6 Pb/
238 U
)]/[(e
rr. 20
7 Pb/
235 U
)/(m
easu
red
207 P
b/23
5 U)].
c D
egre
e of
con
cord
ance
(%);
defin
ed a
s 10
0 ×
[(206 P
b/23
8 U a
ge)/(
207 P
b/20
6 U a
ge)]
d Effe
ctiv
e ag
e; fo
r age
s <1
000
Ma
and
>100
0 M
a, th
is c
orre
spon
ds to
cal
cula
ted
206 P
b/23
8 U a
nd 20
7 Pb/
206 P
b ag
es, r
espe
ctiv
ely.
Isot
opic
Rat
iosa
Age
Est
imat
esa (M
a)E
ff.A
ged
105
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 2.
Hf I
soto
pic
data
Ana
lysi
s17
6 Hf/17
7 Hf
2SE
176 Lu
/177 H
f17
6 Yb/17
7 Hf
Effe
ctiv
eA
geH
f iε H
f1S
ET D
M (G
a)T D
M (c
rust
al)
z002
0.28
2202
0.00
0021
0.00
1087
0.05
0804
1260
0.28
2176
6.85
0.75
1.49
1.62
z020
0.28
1917
0.00
0036
0.00
1012
0.04
7264
1359
0.28
1891
-1.0
21.
281.
882.
18
z021
0.28
2095
0.00
0047
0.00
1688
0.09
0459
1423
0.28
2050
6.05
1.64
1.66
1.79
z026
0.28
2216
0.00
0034
0.00
0918
0.04
6655
953
0.28
2200
0.82
1.20
1.46
1.75
z032
0.28
2037
0.00
0043
0.00
0846
0.03
7086
1414
0.28
2014
4.60
1.52
1.70
1.87
z035
0.28
1941
0.00
0060
0.00
1939
0.08
7501
1373
0.28
1891
-0.7
12.
101.
892.
17
z039
0.28
2079
0.00
0018
0.00
1046
0.04
8973
1332
0.28
2053
4.12
0.62
1.65
1.84
z040
0.28
1702
0.00
0026
0.00
1298
0.05
8879
1829
0.28
1657
1.32
0.92
2.19
2.39
z044
0.28
1832
0.00
0018
0.00
0718
0.03
4082
1515
0.28
1812
-0.3
10.
631.
982.
25
z049
0.28
1719
0.00
0020
0.00
1277
0.05
5006
1852
0.28
1674
2.45
0.69
2.17
2.34
z050
0.28
1977
0.00
0115
0.00
3233
0.14
4551
1359
0.28
1894
-0.9
14.
031.
912.
17
z053
0.28
2009
0.00
0081
0.00
2476
0.09
5874
1204
0.28
1953
-2.2
92.
831.
822.
14
z054
0.28
2121
0.00
0043
0.00
1790
0.07
8769
643
0.28
2099
-9.6
51.
491.
632.
17
z055
0.28
2605
0.00
0027
0.00
1980
0.08
2720
533
0.28
2585
5.14
0.96
0.94
1.16
z056
0.28
1753
0.00
0130
0.00
5146
0.22
3508
637
0.28
1691
-24.
234.
542.
363.
06
z058
0.28
1453
0.00
0017
0.00
1127
0.04
9282
1905
0.28
1412
-5.6
50.
602.
522.
87
z076
0.28
1915
0.00
0043
0.00
1532
0.06
8208
640
0.28
1897
-16.
881.
521.
912.
61
z077
0.28
1921
0.00
0033
0.00
0641
0.03
0235
1233
0.28
1906
-3.3
11.
151.
852.
22
z078
0.28
2095
0.00
0043
0.00
1416
0.06
8720
1238
0.28
2061
2.31
1.50
1.65
1.88
z086
0.28
2250
0.00
0051
0.00
3090
0.12
8135
1086
0.28
2186
3.33
1.79
1.50
1.70
z089
0.28
1928
0.00
0017
0.00
0732
0.03
2237
1593
0.28
1906
4.78
0.59
1.85
2.00
z091
0.28
2124
0.00
0017
0.00
0754
0.03
9016
1261
0.28
2106
4.39
0.59
1.58
1.77
z094
0.28
2158
0.00
0041
0.00
1825
0.07
7317
631
0.28
2137
-8.5
71.
431.
582.
09
z104
0.28
2013
0.00
0027
0.00
1310
0.06
0983
564
0.28
1999
-14.
940.
931.
762.
44
z121
0.28
3147
0.00
3372
0.00
1951
0.08
8610
651
0.28
3123
26.7
911
8.02
0.15
-0.1
2
z142
0.28
1566
0.00
0035
0.00
1264
0.05
2733
1875
0.28
1521
-2.4
51.
232.
382.
66
z143
0.28
1965
0.00
0022
0.00
0689
0.03
0555
1265
0.28
1948
-1.1
00.
761.
802.
11
z154
0.28
2051
0.00
0090
0.00
1603
0.05
6675
682
0.28
2031
-11.
213.
161.
722.
29
z156
0.28
2244
0.00
0019
0.00
1230
0.05
9379
528
0.28
2232
-7.5
00.
681.
431.
95
z159
0.28
2046
0.00
0017
0.00
0870
0.04
0722
1294
0.28
2024
2.24
0.59
1.69
1.93
z163
0.28
1896
0.00
0089
0.00
2420
0.09
2515
598
0.28
1869
-18.
783.
121.
982.
70
z165
0.28
1610
0.00
0016
0.00
0666
0.02
9699
1918
0.28
1586
0.81
0.57
2.28
2.49
Lu d
ecay
con
stan
t 1.8
65 x
10-1
1 Sch
erer
et a
l. (2
001)
BD
M01
106
Chapter 5 Age and provenance of the northern Paraguay BeltTa
ble
2. (c
ontin
ued)
Ana
lysi
s17
6 Hf/17
7 Hf
2SE
176 Lu
/177 H
f17
6 Yb/17
7 Hf
Effe
ctiv
eA
geH
f iε H
f1S
ET D
M (G
a)T D
M (c
rust
al)
z170
0.28
1819
0.00
0119
0.00
3533
0.22
6737
948
0.28
1756
-15.
004.
182.
162.
72
z173
0.28
2144
0.00
0041
0.00
2254
0.12
5614
1163
0.28
2095
1.78
1.43
1.62
1.85
z176
0.28
2098
0.00
0022
0.00
2219
0.11
1463
1379
0.28
2040
4.73
0.76
1.68
1.84
z180
0.28
2044
0.00
0032
0.00
0957
0.04
7635
1429
0.28
2018
5.06
1.13
1.70
1.86
z183
0.28
2302
0.00
0052
0.00
0819
0.04
1151
1015
0.28
2286
5.26
1.82
1.34
1.53
z184
0.28
2206
0.00
0051
0.00
1299
0.04
8133
1042
0.28
2181
2.13
1.78
1.49
1.74
z185
0.28
1595
0.00
0015
0.00
0317
0.01
3594
1950
0.28
1583
1.44
0.52
2.28
2.48
z187
0.28
2198
0.00
0046
0.00
0854
0.03
8270
608
0.28
2188
-7.2
61.
621.
482.
00
z188
0.28
2457
0.00
0047
0.00
0919
0.03
9194
548
0.28
2447
0.56
1.63
1.12
1.46
z195
0.28
1542
0.00
0018
0.00
0956
0.04
6765
1805
0.28
1509
-4.4
90.
632.
392.
72
z002
0.28
1198
449
1.26
013E-‐05
0.00
0666
673
0.02
4058
936
1896
0.28
1174
46-‐14.31
0.44
2.84
3.38
z003
0.28
1846
299
1.32
359E-‐05
0.00
0584
277
0.02
2597
468
1594
0.28
1828
667
2.08
0.46
1.95
2.17
z023
0.28
1917
098
1.54
824E-‐05
0.00
0680
529
0.03
1225
898
1571
0.28
1896
866
3.97
0.54
1.86
2.03
z026
0.28
2235
369
1.51
202E-‐05
0.00
0536
581
0.02
4725
043
1031
0.28
2224
951
3.46
0.53
1.42
1.65
z033
0.28
1755
376
2.41
959E-‐05
0.00
1385
999
0.05
0535
5217
990.28
1708
095
2.44
0.85
2.12
2.30
z037
0.28
2230
021.67
906E-‐05
0.00
1194
964
0.05
5464
069
1065
0.28
2206
038
3.56
0.59
1.45
1.67
z040
0.28
1927
467
1.80
277E-‐05
0.00
0643
0.02
8184
145
1433
0.28
1910
057
1.31
0.63
1.85
2.09
z045
0.28
2270
054
2.21
982E-‐05
0.00
1475
649
0.07
3237
775
1090
0.28
2239
758
5.30
0.78
1.40
1.58
z047
0.28
1963
203
1.37
276E-‐05
0.00
0472
302
0.01
7876
1114
170.28
1950
559
2.39
0.48
1.79
2.01
z049
0.28
1767
418
1.97
465E-‐05
0.00
1056
833
0.03
9243
8217
380.28
1732
603
1.93
0.69
2.09
2.29
z051
0.28
1923
918
1.54
809E-‐05
0.00
0639
252
0.02
3712
565
1411
0.28
1906
868
0.72
0.54
1.85
2.11
z053
0.28
1910
673
1.33
45E-‐05
0.00
0100
845
0.00
4211
988
0.28
1908
797
-‐8.70
0.47
1.84
2.37
z054
0.28
1979
908
3.02
6E-‐05
0.00
2012
451
0.06
5451
331
1565
0.28
1920
324.66
1.06
1.84
1.99
z057
0.28
1854
972
1.52
719E-‐05
0.00
0884
616
0.03
4979
682
1580
0.28
1828
519
1.75
0.53
1.96
2.18
z062
0.28
2226
515
2.04
087E-‐05
0.00
0622
793
0.02
0020
348
1032
0.28
2214
407
3.11
0.71
1.43
1.67
z067
0.28
1910
779
2.82
427E-‐05
0.00
1866
978
0.07
8865
716
1559
0.28
1855
717
2.23
0.99
1.93
2.13
z069
0.28
2069
785
3.24
699E-‐05
0.00
0730
167
0.02
8320
051
987
0.28
2056
223
-‐3.51
1.14
1.65
2.05
z077
0.28
1822
501
2.02
217E-‐05
0.00
1203
747
0.04
1507
378
1682
0.28
1784
154
2.48
0.71
2.02
2.21
z080
0.28
2171
773
1.44
958E-‐05
0.00
0358
675
0.01
3337
603
1056
0.28
2164
641
1.87
0.51
1.50
1.77
z082
0.28
2109
346
1.56
94E-‐05
0.00
0677
782
0.02
8489
474
1271
0.28
2093
094
4.15
0.55
1.60
1.79
z083
0.28
2201
425
1.60
781E-‐05
0.00
0723
140.03
3280
903
968
0.28
2188
251
0.75
0.56
1.47
1.77
z093
0.28
1747
644
1.86
922E-‐05
0.00
0736
706
0.02
8861
295
1688
0.28
1724
082
0.49
0.65
2.10
2.33
BP
UG
02
Lu d
ecay
con
stan
t 1.8
65 x
10-1
1 Sch
erer
et a
l. (2
001)
107
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 2.
(con
tinue
d)
Ana
lysi
s17
6 Hf/17
7 Hf
2SE
176 Lu
/177 H
f17
6 Yb/17
7 Hf
Effe
ctiv
eA
geH
f iε H
f1S
ET D
M (G
a)T D
M (c
rust
al)
z095
0.28
1850
029
1.72
039E-‐05
0.00
0726
335
0.03
1164
761
1518
0.28
1829
168
0.38
0.60
1.96
2.21
z099
0.28
2151
041
1.58
664E-‐05
0.00
0694
906
0.02
9749
521
1215
0.28
2135
117
4.39
0.56
1.54
1.73
z100
0.28
1803
771.78
194E-‐05
0.00
0986
177
0.03
7105
666
1540
0.28
1775
045
-‐1.06
0.62
2.03
2.32
z101
0.28
1852
686
1.42
79E-‐05
0.00
0621
789
0.02
7034
267
1511
0.28
1834
910.43
0.50
1.95
2.20
z103
0.28
1961
61.75
476E-‐05
0.00
1060
497
0.04
1795
096
1351
0.28
1934
540.34
0.61
1.82
2.09
z104
0.28
1864
189
1.54
122E-‐05
0.00
0628
553
0.02
8582
558
1546
0.28
1845
798
1.60
0.54
1.93
2.16
z107
0.28
1720
712
1.65
859E-‐05
0.00
1131
310.04
1563
894
1765
0.28
1682
855
0.78
0.58
2.16
2.38
z116
0.28
1837
023
2.30
291E-‐05
0.00
1607
313
0.07
7190
484
1668
0.28
1786
252
2.23
0.81
2.02
2.21
z119
0.28
1872
116
2.24
953E-‐05
0.00
1139
20.03
8115
237
1467
0.28
1840
52-‐0.38
0.79
1.95
2.22
z120
0.28
1919
837
5.92
85E-‐05
0.00
4567
115
0.25
0930
823
1545
0.28
1786
369
-‐0.55
2.07
2.07
2.29
z122
0.28
1477
598
1.91
382E-‐05
0.00
1460
856
0.05
8625
428
1975
0.28
1422
8-‐3.69
0.67
2.51
2.81
z127
0.28
1834
734
1.55
062E-‐05
0.00
0542
084
0.01
9933
195
1487
0.28
1819
487
-‐0.66
0.54
1.97
2.25
z128
0.28
2209
728
0.00
0014
590.00
0628
777
0.02
4605
466
1015
0.28
2197
707
2.14
0.51
1.46
1.72
z002
0.28
2128
832.86
058E-‐05
0.00
1499
696
0.05
3242
807
1153
0.28
2096
224
1.63
1.00
1.60
1.86
z010
0.28
2042
698
2.58
833E-‐05
0.00
1508
621
0.06
2566
707
1414
0.28
2002
373
4.18
0.91
1.73
1.90
z014
0.28
2004
338
3.08
782E-‐05
0.00
1931
120.06
7832
575
1518
0.28
1948
871
4.63
1.08
1.80
1.95
z016
0.28
2076
376
3.04
149E-‐05
0.00
0595
632
0.02
2121
893
1111
0.28
2063
907
-‐0.46
1.06
1.64
1.95
z019
0.28
2236
996
1.67
778E-‐05
0.00
0446
606
0.02
0787
8893
00.28
2229
184
1.34
0.59
1.41
1.70
z024
0.28
2251
134
2.22
346E-‐05
0.00
0691
847
0.03
4108
537
903
0.28
2239
381.11
0.78
1.40
1.70
z025
0.28
1809
992.33
802E-‐05
0.00
0795
543
0.03
2342
213
1553
0.28
1786
617
-‐0.35
0.82
2.01
2.28
z029
0.28
2239
465
2.90
863E-‐05
0.00
0626
874
0.03
0447
154
1107
0.28
2226
392
5.20
1.02
1.42
1.60
z034
0.28
2025
061
2.84
811E-‐05
0.00
1288
760.05
9254
381
1584
0.28
1986
433
7.44
1.00
1.74
1.83
z038
0.28
2250
654
3.38
477E-‐05
0.00
0962
862
0.03
4538
843
942
0.28
2233
594
1.77
1.18
1.41
1.69
z042
0.28
2039
987
1.76
383E-‐05
0.00
0475
210.02
2063
018
1322
0.28
2028
125
3.01
0.62
1.68
1.90
z043
0.28
2239
671
4.72
318E-‐05
0.00
1121
641
0.03
8838
128
903
0.28
2220
620.44
1.65
1.43
1.74
z057
0.28
1896
053
0.00
0132
738
0.00
1268
197
0.04
3865
043
1340
0.28
1863
965
-‐2.41
4.65
1.92
2.25
z061
0.28
2006
993
2.22
668E-‐05
0.00
0988
032
0.04
4939
097
1382
0.28
1981
194
2.70
0.78
1.75
1.97
z062
0.28
2191
779
2.92
242E-‐05
0.00
0441
161
0.02
1137
678
926
0.28
2184
097
-‐0.35
1.02
1.47
1.81
z069
0.28
2030
859
3.44
692E-‐05
0.00
0753
643
0.03
0500
4715
170.28
2009
235
6.74
1.21
1.71
1.82
z071
0.28
2283
362
3.14
719E-‐05
0.00
0715
422
0.03
6069
356
636
0.28
2274
826
-‐3.58
1.10
1.36
1.79
z072
0.28
2160
312
2.48
33E-‐05
0.00
0422
275
0.02
1612
204
1033
0.28
2152
101
0.91
0.87
1.52
1.81
z073
0.28
2117
685
3.15
021E-‐05
0.00
1260
846
0.04
5374
0711
980.28
2089
192.39
1.10
1.61
1.84
BR
Z01
Lu d
ecay
con
stan
t 1.8
65 x
10-1
1 Sch
erer
et a
l. (2
001)
108
Chapter 5 Age and provenance of the northern Paraguay BeltTa
ble
2. (c
ontin
ued)
Ana
lysi
s17
6 Hf/17
7 Hf
2SE
176 Lu
/177 H
f17
6 Yb/17
7 Hf
Effe
ctiv
eA
geH
f iε H
f1S
ET D
M (G
a)T D
M (c
rust
al)
z075
0.28
2014
393
3.13
864E-‐05
0.00
1430
319
0.05
8773
3812
920.28
1979
512
0.61
1.10
1.76
2.03
z076
0.28
1453
358
2.42
648E-‐05
0.00
0729
206
0.03
2184
588
1984
0.28
1425
869
-‐3.36
0.85
2.50
2.79
z077
0.28
2117
568
1.82
341E-‐05
0.00
0866
721
0.03
8045
109
1193
0.28
2098
066
2.59
0.64
1.59
1.83
z080
0.28
2257
984
2.48
379E-‐05
0.00
0539
668
0.02
5473
086
928
0.28
2248
561
1.99
0.87
1.39
1.66
z086
0.28
2167
384
4.18
179E-‐05
0.00
0961
641
0.03
4320
089
1238
0.28
2144
915
5.27
1.46
1.53
1.70
z095
0.28
2262
397
2.36
917E-‐05
0.00
0862
248
0.03
3846
586
945
0.28
2247
074
2.31
0.83
1.39
1.66
z097
0.28
2062
042
2.75
152E-‐05
0.00
0925
814
0.03
4522
738
1235
0.28
2040
465
1.50
0.96
1.67
1.93
z109
0.28
1971
637
2.53
614E-‐05
0.00
0887
777
0.03
4261
948
1391
0.28
1948
305
1.73
0.89
1.80
2.03
z115
0.28
2230
848
2.49
233E-‐05
0.00
0783
521
0.03
3674
217
983
0.28
2216
346
2.08
0.87
1.43
1.70
z119
0.28
2219
52.69
084E-‐05
0.00
0386
145
0.01
8563
489
1053
0.28
2211
839
3.49
0.94
1.43
1.67
z124
0.28
2127
797
2.42
206E-‐05
0.00
1026
069
0.04
7867
183
1165
0.28
2105
256
2.22
0.85
1.59
1.83
z131
0.28
2160
651
1.98
365E-‐05
0.00
0572
007
0.02
5571
331
908
0.28
2150
878
-‐1.91
0.69
1.52
1.89
z137
0.28
2003
415.01
035E-‐05
0.00
0795
252
0.02
8944
545
1278
0.28
1984
231
0.46
1.75
1.75
2.02
z001
0.28
1978
011
2.21
08E-‐05
0.00
1008
060.03
9684
995
1490
0.28
1949
614.01
0.77
1.79
1.97
z002
0.28
2254
733
2.02
35E-‐05
0.00
0771
837
0.03
3111
552
937
0.28
2241
128
1.93
0.71
1.40
1.67
z005
0.28
1890
821.64
433E-‐05
0.00
0710
051
0.03
1044
902
1556
0.28
1869
912.68
0.58
1.90
2.10
z006
0.28
1971
043
1.91
757E-‐05
0.00
0749
104
0.03
0001
075
1367
0.28
1951
71.31
0.67
1.79
2.04
z008
0.28
1922
777
1.34
642E-‐05
0.00
0753
490.03
2182
815
290.28
1900
979
3.17
0.47
1.86
2.05
z009
0.28
2259
757
2.15
51E-‐05
0.00
0753
70.02
9793
427
1074
0.28
2244
513
5.11
0.75
1.39
1.58
z010
0.28
1974
645
1.87
146E-‐05
0.00
1368
487
0.05
6009
954
1486
0.28
1936
183
3.45
0.66
1.82
2.00
z014
0.28
2159
011.62
013E-‐05
0.00
0541
704
0.02
1737
318
1049
0.28
2148
313
1.13
0.57
1.52
1.81
z015
0.28
1769
011.25
155E-‐05
0.00
0290
995
0.00
8836
5715
420.28
1760
519
-‐1.52
0.44
2.04
2.35
z016
0.28
2001
071
2.01
9E-‐05
0.00
0951
293
0.03
8662
163
1372
0.28
1976
408
2.31
0.71
1.76
1.98
z001
0.28
1933
601
2.55
857E
-05
0.00
1180
871
0.04
9372
636
1675
0.28
1896
6.29
0.9
1.86
1.97
z005
0.28
2112
553
1.57
486E
-05
0.00
0667
681
0.02
5080
651
1211
0.28
2097
2.98
0.6
1.59
1.82
z008
0.28
1842
321
2.39
767E-‐05
0.00
1260
253
0.03
3879
5515
610.28
1805
0.48
0.8
1.99
2.24
z010
0.28
1891
877
1.70
357E
-05
0.00
0444
611
0.01
3905
318
1662
0.28
1878
5.35
0.6
1.89
2.02
z018
0.28
2191
386
1.95
546E
-05
0.00
0984
524
0.02
9382
254
943
0.28
2174
-‐0.31
0.7
1.50
1.82
z021
0.28
2099
167
2.60
518E
-05
0.00
0829
115
0.02
5039
099
1606
0.28
2074
11.05
0.9
1.62
1.63
z023
0.28
2300
267
2.79
392E
-05
0.00
3389
237
0.13
2016
232
1079
0.28
2231
4.75
1.0
1.44
1.61
z028
0.28
1884
754
2.02
307E
-05
0.00
1380
370.05
0848
513
1571
0.28
1844
2.09
0.7
1.94
2.15
BR
Z-02
BR
Z-15
Lu d
ecay
con
stan
t 1.8
65 x
10-1
1 Sch
erer
et a
l. (2
001)
109
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 2.
(con
tinue
d)
Ana
lysi
s17
6 Hf/17
7 Hf
2SE
176 Lu
/177 H
f17
6 Yb/17
7 Hf
Effe
ctiv
eA
geH
f iε H
f1S
ET D
M (G
a)T D
M (c
rust
al)
z029
0.28
1835
929
2.40
006E
-05
0.00
1306
754
0.05
1569
794
1602
0.28
1796
1.11
0.8
2.01
2.23
z030
0.28
2001
571
2.03
108E
-05
0.00
0731
965
0.02
6229
733
1315
0.28
1983
1.27
0.7
1.75
2.00
z038
0.28
2101
222.57
444E
-05
0.00
0826
485
0.02
5051
249
1184
0.28
2083
1.84
0.9
1.61
1.87
z039
0.28
1829
806
2.44
952E
-05
0.00
2028
568
0.07
5118
008
1818
0.28
1760
4.72
0.9
2.05
2.18
z041
0.28
2118
468
2.64
991E
-05
0.00
1363
816
0.04
0582
7811
620.28
2089
1.55
0.9
1.61
1.87
z047
0.28
2119
484
1.76
207E-‐05
0.00
0854
461
0.03
0333
816
1140
0.28
2101
1.50
0.6
1.59
1.85
z055
0.28
1926
681
2.88
956E
-05
0.00
1431
529
0.04
4180
015
1573
0.28
1884
3.56
1.0
1.89
2.06
z065
0.28
1859
137
1.47
598E
-05
0.00
0473
805
0.01
6723
603
1535
0.28
1845
1.33
0.5
1.93
2.17
z066
0.28
1826
167
1.88
446E
-05
0.00
0898
224
0.03
2327
113
770.28
1803
-‐3.74
0.7
2.00
2.36
z067
0.28
2111
291.78
618E
-05
0.00
0585
167
0.01
7869
367
1028
0.28
2100
-‐1.03
0.6
1.59
1.93
z068
0.28
1889
223
1.35
799E
-05
0.00
0754
573
0.02
7968
005
1585
0.28
1867
3.22
0.5
1.90
2.09
z077
0.28
1529
861.75
019E
-05
0.00
0827
754
0.02
9623
744
1752
0.28
1502
-‐5.92
0.6
2.40
2.77
z086
0.28
1989
521
2.94
685E
-05
0.00
1214
236
0.03
3025
171
1504
0.28
1955
4.53
1.0
1.79
1.95
z095
0.28
1983
762
1.46
077E
-05
0.00
0405
816
0.01
3709
231
1338
0.28
1974
1.43
0.5
1.76
2.01
z100
0.28
1858
419
1.52
701E
-05
0.00
1220
402
0.04
4543
192
1622
0.28
1821
2.44
0.5
1.97
2.17
z108
0.28
2206
473
2.40
785E
-05
0.00
1212
394
0.03
3667
486
929
0.28
2185
-‐0.22
0.8
1.48
1.80
z118
0.28
0612
452
5.75
019E
-05
0.00
1117
398
0.03
0218
106
3083
0.28
0546
-‐9.29
2.0
3.67
3.98
z119
0.28
1831
948
4.93
342E
-05
0.00
2604
770.08
1523
025
1706
0.28
1748
1.74
1.7
2.08
2.27
z120
0.28
1915
548
0.00
0016
963
0.00
0569
652
0.02
0596
762
1308
0.28
1901
-‐1.80
0.6
1.86
2.18
z127
0.28
1839
921
1.71
499E
-05
0.00
0703
904
0.02
3094
505
1366
0.28
1822
-‐3.32
0.6
1.97
2.32
z131
0.28
2122
839
2.15
485E
-05
0.00
0861
477
0.02
5217
513
1240
0.28
2103
3.80
0.8
1.59
1.79
z133
0.28
2079
280.00
0025
60.00
0808
091
0.02
3959
257
1187
0.28
2061
1.16
0.9
1.64
1.91
z135
0.28
2211
664
1.45
567E
-05
0.00
0601
586
0.02
1055
476
942
0.28
2201
0.61
0.5
1.45
1.76
z139
0.28
2015
083
2.08
102E
-05
0.00
0723
391
0.02
1269
626
1203
0.28
1999
-‐0.71
0.7
1.73
2.04
z147
0.28
1792
216
3.47
648E
-05
0.00
0859
946
0.02
5285
9915
440.28
1767
-‐1.25
1.2
2.04
2.33
z158
0.28
1854
719
1.58
543E
-05
0.00
0766
039
0.02
8239
269
1525
0.28
1833
0.66
0.6
1.95
2.20
z162
0.28
1948
596
1.78
788E
-05
0.00
0830
411
0.02
8547
289
1523
0.28
1925
3.87
0.6
1.83
2.00
z005
0.28
1827
232.11
152E-‐05
0.00
0520
396
0.02
3607
077
1431
0.28
1813
158
-‐2.17
0.74
1.98
2.30
z006
0.28
2058
161.93
916E-‐05
0.00
0629
767
0.02
6841
575
1268
0.28
2043
093
2.32
0.68
1.67
1.90
z007
0.28
2128
234
2.72
961E-‐05
0.00
0750
940.03
2738
824
1185
0.28
2111
462.87
0.96
1.57
1.80
z009
0.28
2226
832
3.38
412E-‐05
0.00
0575
057
0.02
3395
464
918
0.28
2216
903
0.64
1.18
1.43
1.74
z015
0.28
1867
985
1.65
014E-‐05
0.00
0520
903
0.02
3376
455
1555
0.28
1852
662.04
0.58
1.92
2.14
BR
Z-24
Lu d
ecay
con
stan
t 1.8
65 x
10-1
1 Sch
erer
et a
l. (2
001)
110
Chapter 5 Age and provenance of the northern Paraguay BeltTa
ble
2. (c
ontin
ued)
Ana
lysi
s17
6 Hf/17
7 Hf
2SE
176 Lu
/177 H
f17
6 Yb/17
7 Hf
Effe
ctiv
eA
geH
f iε H
f1S
ET D
M (G
a)T D
M (c
rust
al)
z020
0.28
2183
834
1.73
334E-‐05
0.00
0491
068
0.02
4949
610
170.28
2174
435
1.34
0.61
1.49
1.77
z022
0.28
2271
988
1.86
501E-‐05
0.00
0537
760.02
4937
914
615
0.28
2265
788
-‐4.37
0.65
1.37
1.82
z023
0.28
2200
172
1.75
432E-‐05
0.00
0835
290.04
0204
263
932
0.28
2185
526
-‐0.15
0.61
1.48
1.80
z027
0.28
2095
472
1.66
23E-‐05
0.00
0694
861
0.03
2275
514
1161
0.28
2080
261.24
0.58
1.62
1.89
z028
0.28
2154
648
1.43
712E-‐05
0.00
0419
130.01
8735
481
934
0.28
2147
282
-‐1.46
0.50
1.52
1.88
z030
0.28
1847
641
1.69
888E-‐05
0.00
0793
785
0.03
2709
185
1535
0.28
1824
590.59
0.59
1.96
2.21
z034
0.28
2097
012
1.77
455E-‐05
0.00
0489
485
0.02
2228
686
737
0.28
2090
238
-‐7.88
0.62
1.61
2.13
z037
0.28
2129
357
1.38
878E-‐05
0.00
0510
464
0.02
0558
369
1219
0.28
2117
616
3.87
0.49
1.56
1.77
z038
0.28
1546
161.96
952E-‐05
0.00
0986
088
0.04
1878
389
1767
0.28
1513
132
-‐5.21
0.69
2.39
2.74
z041
0.28
2225
895
1.64
372E-‐05
0.00
0665
252
0.03
0921
518
1004
0.28
2213
318
2.44
0.58
1.44
1.69
z047
0.28
2145
357
2.35
393E-‐05
0.00
1447
215
0.07
5056
178
1334
0.28
2108
903
6.14
0.82
1.58
1.72
z049
0.28
2147
744
1.48
591E-‐05
0.00
0362
306
0.01
6141
752
942
0.28
2141
326
-‐1.51
0.52
1.53
1.89
z055
0.28
1863
244
1.52
271E-‐05
0.00
0875
815
0.03
7530
102
1538
0.28
1837
752
1.14
0.53
1.95
2.18
z058
0.28
2074
451.76
259E-‐05
0.00
0728
349
0.03
0412
769
1212
0.28
2057
797
1.59
0.62
1.65
1.90
z062
0.28
2074
451.76
259E-‐05
0.00
0728
349
0.03
0412
769
1285
0.28
2056
782
3.20
0.62
1.65
1.86
z071
0.28
1831
448
2.07
086E-‐05
0.00
0967
468
0.04
4511
878
1730
0.28
1799
722
4.13
0.72
1.99
2.15
z079
0.28
2135
704
1.71
096E-‐05
0.00
0616
412
0.02
7351
2311
980.28
2121
782
3.53
0.60
1.56
1.77
z084
0.28
2089
312
1.61
23E-‐05
0.00
0679
821
0.03
0568
744
1245
0.28
2073
337
2.89
0.56
1.63
1.85
z091
0.28
2035
447
1.65
051E-‐05
0.00
0935
264
0.03
9804
688
1368
0.28
2011
283
3.44
0.58
1.71
1.91
z096
0.28
2216
111
1.67
121E-‐05
0.00
0413
965
0.01
8880
685
949
0.28
2208
721
1.04
0.58
1.44
1.74
z099
0.28
1939
656
1.59
746E-‐05
0.00
0492
112
0.02
1106
295
1498
0.28
1925
712
3.35
0.56
1.82
2.02
z125
0.28
1631
938
1.98
516E-‐05
0.00
1150
138
0.05
1859
717
1789
0.28
1592
923
-‐1.88
0.69
2.28
2.55
z130
0.28
2171
921
1.51
597E-‐05
0.00
0330
445
0.01
3942
563
969
0.28
2165
895
-‐0.02
0.53
1.50
1.82
z131
0.28
1511
741
1.43
492E-‐05
0.00
0493
768
0.02
0515
944
1916
0.28
1493
775
-‐2.49
0.50
2.40
2.69
z132
0.28
1965
889
1.68
378E-‐05
0.00
0543
825
0.02
6570
278
1373
0.28
1951
782
1.45
0.59
1.79
2.04
z143
0.28
2187
022
1.63
009E-‐05
0.00
0527
988
0.02
6069
775
948
0.28
2177
602
-‐0.07
0.57
1.48
1.81
z146
0.28
2139
446
1.86
416E-‐05
0.00
0664
60.02
7341
641
1140
0.28
2125
172.35
0.65
1.56
1.80
z153
0.28
2150
036
1.65
548E-‐05
0.00
0596
346
0.02
6767
152
1096
0.28
2137
722
1.82
0.58
1.54
1.80
z155
0.28
2167
802
1.98
2E-‐05
0.00
0882
074
0.03
8058
218
1182
0.28
2148
149
4.11
0.69
1.52
1.73
z159
0.28
1528
727
2.22
939E-‐05
0.00
0873
265
0.04
0471
142
1791
0.28
1499
069
-‐5.16
0.78
2.40
2.75
z161
0.28
2194
896
1.74
203E-‐05
0.00
0675
124
0.02
7401
563
991
0.28
2182
305
1.05
0.61
1.48
1.77
z165
0.28
2218
675
1.46
653E-‐05
0.00
0508
479
0.02
3429
997
941
0.28
2209
672
0.90
0.51
1.44
1.74
z167
0.28
1824
492.64
419E-‐05
0.00
2010
561
0.07
9238
404
1674
0.28
1760
745
1.47
0.93
2.06
2.26
Lu d
ecay
con
stan
t 1.8
65 x
10-1
1 Sch
erer
et a
l. (2
001)
111
Chapter 5 Age and provenance of the northern Paraguay Belt
Tabl
e 2.
(con
tinue
d)
Ana
lysi
s17
6 Hf/17
7 Hf
2SE
176 Lu
/177 H
f17
6 Yb/17
7 Hf
Effe
ctiv
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geH
f iε H
f1S
ET D
M (G
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M (c
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z001
0.28
2079
205
0.00
0107
392
0.00
0496
157
0.01
7649
047
1249
0.28
2067
508
2.77
3.76
1.63
1.86
z004
0.28
1905
103
0.00
0138
403
0.00
1410
515
0.04
8508
384
1488
0.28
1865
414
0.98
4.84
1.91
2.15
z005
0.28
2088
001
0.00
0115
429
0.00
0608
981
0.02
1672
129
932
0.28
2077
32-‐3.98
4.04
1.62
2.03
z023
0.28
2145
385
0.00
0117
031
0.00
0948
382
0.03
2072
763
1300
0.28
2122
109
5.85
4.10
1.56
1.71
z026
0.28
2204
205
0.00
0130
039
0.00
0612
408
0.02
1484
812
1217
0.28
2190
152
6.38
4.55
1.46
1.61
z030
0.28
2122
140.00
0132
129
0.00
0607
136
0.02
0169
8210
460.28
2110
18-‐0.28
4.62
1.58
1.89
z045
0.28
2248
783
1.41
283E-‐05
0.00
0434
905
0.01
6331
756
984
0.28
2240
732.96
0.49
1.40
1.65
z047
0.28
2079
121.53
118E-‐05
0.00
0692
779
0.02
4658
922
1211
0.28
2063
294
1.76
0.54
1.64
1.89
z048
0.28
2168
103
1.38
004E-‐05
0.00
0601
232
0.02
1760
902
1006
0.28
2156
713
0.48
0.48
1.51
1.82
z049
0.28
2215
163
1.92
566E-‐05
0.00
1226
291
0.04
3576
181
1078
0.28
2190
254
3.28
0.67
1.47
1.70
z051
0.28
2290
805
1.69
542E-‐05
0.00
0966
204
0.03
7277
902
911
0.28
2274
257
2.51
0.59
1.36
1.62
z059
0.28
2002
324
1.75
882E-‐05
0.00
0903
826
0.02
9609
296
1401
0.28
1978
397
3.03
0.62
1.76
1.96
z060
0.28
2179
551.92
115E-‐05
0.00
1159
336
0.04
3120
822
651
0.28
2165
384
-‐7.12
0.67
1.52
2.02
z078
0.28
1778
986.67
475E-‐05
0.00
0907
352
0.03
0581
545
1542
0.28
1752
503
-‐1.80
2.34
2.06
2.36
z091
0.28
2252
120.00
0155
578
0.00
0602
551
0.02
1202
021
1065
0.28
2240
029
4.76
5.45
1.40
1.60
z098
0.28
2418
627
0.00
0178
423
0.00
1958
330.07
4591
868
662
0.28
2394
311.22
6.24
1.21
1.51
z107
0.28
1898
872
0.00
0122
277
0.00
0570
489
0.01
8691
4710
720.28
1887
347
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4.28
1.88
2.36
z108
0.28
2161
293
0.00
0147
197
0.00
0876
466
0.02
8721
005
993
0.28
2144
904
-‐0.22
5.15
1.53
1.85
z112
0.28
2095
60.00
0118
707
0.00
0768
308
0.02
8017
6212
070.28
2078
114
2.19
4.15
1.62
1.86
z115
0.28
2195
658
0.00
0142
037
0.00
0658
738
0.02
5401
432
899
0.28
2184
52-‐0.92
4.97
1.48
1.82
z117
0.28
2241
091
0.00
0113
956
0.00
0757
813
0.02
8891
856
881
0.28
2228
534
0.24
3.99
1.42
1.74
z120
0.28
2074
668
0.00
0102
435
0.00
0613
339
0.02
1440
117
1155
0.28
2061
317
0.42
3.59
1.64
1.93
z130
0.28
2139
669
0.00
0207
932
0.00
0700
411
0.02
4801
891
962
0.28
2126
987
-‐1.55
7.28
1.56
1.91
z20.28
2158
362
3.81
103E-‐05
0.00
1318
861
0.06
8994
791
1196
0.28
2129
3.73
1.33
1.56
1.76
z40.28
2183
215
2.73
536E-‐05
0.00
0483
405
0.02
4028
442
989
0.28
2174
0.71
0.96
1.49
1.79
z50.28
1595
239
3.12
365E-‐05
0.00
0503
224
0.02
5624
939
906
0.28
1587
-‐21.96
1.09
2.29
3.11
z80.28
2172
555
4.28
955E-‐05
0.00
0649
732
0.03
5016
7711
930.28
2158
4.71
1.50
1.51
1.70
z12
0.28
1820
342
3.42
188E-‐05
0.00
0993
033
0.04
8653
019
1479
0.28
1793
-‐1.80
1.20
2.01
2.31
z13
0.28
2222
275
3.18
19E-‐05
0.00
0399
616
0.02
0676
679
930
0.28
2215
0.84
1.11
1.43
1.73
z14
0.28
1846
094
3.30
238E-‐05
0.00
0731
133
0.03
6589
204
1581
0.28
1824
1.63
1.16
1.96
2.18
z16
0.28
1649
593
3.63
093E-‐05
0.00
2431
584
0.10
6283
575
1863
0.28
1564
-‐1.23
1.27
2.33
2.57
BS
A-0
7
BS
A-2
0
Lu d
ecay
con
stan
t 1.8
65 x
10-1
1 Sch
erer
et a
l. (2
001)
112
Chapter 5 Age and provenance of the northern Paraguay BeltTa
ble
2. (c
ontin
ued)
Ana
lysi
s17
6 Hf/17
7 Hf
2SE
176 Lu
/177 H
f17
6 Yb/17
7 Hf
Effe
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f iε H
f1S
ET D
M (G
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z17
0.28
2022
929
3.12
73E-‐05
0.00
0738
015
0.03
7199
134
1339
0.28
2004
2.54
1.09
1.72
1.94
z25
0.28
2271
904
2.73
745E-‐05
0.00
0648
939
0.03
2109
583
949
0.28
2260
2.88
0.96
1.37
1.62
z28
0.28
2212
324
2.95
451E-‐05
0.00
0807
265
0.03
9208
583
1252
0.28
2193
7.28
1.03
1.46
1.58
z32
0.28
2229
847
3.42
893E-‐05
0.00
0621
083
0.03
0807
693
984
0.28
2218
2.17
1.20
1.43
1.69
z35
0.28
2201
899
4.60
161E-‐05
0.00
1542
453
0.05
6428
966
1091
0.28
2170
2.86
1.61
1.50
1.73
z36
0.28
2204
863
4.61
269E-‐05
0.00
1520
301
0.05
5887
092
940
0.28
2178
-‐0.24
1.61
1.50
1.81
z37
0.28
2175
283
3.00
845E-‐05
0.00
0760
472
0.03
2217
727
719
0.28
2165
-‐5.62
1.05
1.51
1.98
z40
0.28
2169
704
2.73
044E-‐05
0.00
0514
289
0.02
4469
396
1074
0.28
2159
2.09
0.96
1.51
1.77
z41
0.28
2002
705
2.97
276E-‐05
0.00
0863
197
0.04
4632
313
1359
0.28
1981
2.16
1.04
1.75
1.98
z47
0.28
2192
965
2.99
326E-‐05
0.00
0499
434
0.02
5302
168
970
0.28
2184
0.64
1.05
1.47
1.78
z53
0.28
1862
532
3.60
735E-‐05
0.00
0915
407
0.04
2866
115
800.28
1835
1.99
1.26
1.95
2.16
z56
0.28
2222
968
3.91
353E-‐05
0.00
0899
106
0.04
2813
2111
000.28
2204
4.27
1.37
1.45
1.65
z68
0.28
2076
218
3.21
906E-‐05
0.00
0634
062
0.03
0785
266
1283
0.28
2061
3.30
1.13
1.64
1.85
z70
0.28
2077
109
3.42
905E-‐05
0.00
0496
419
0.02
2938
812
1212
0.28
2066
1.87
1.20
1.63
1.89
z76
0.28
2207
582
8.04
165E-‐05
0.00
1075
615
0.03
7291
052
653
0.28
2194
-‐6.05
2.81
1.48
1.95
z77
0.28
1559
188
5.24
001E-‐05
0.00
0844
466
0.04
1830
947
1808
0.28
1530
-‐3.66
1.83
2.36
2.68
z78
0.28
2127
056
3.00
233E-‐05
0.00
0550
778
0.02
6144
9711
960.28
2115
3.24
1.05
1.57
1.79
z89
0.28
2147
085
4.11
244E-‐05
0.00
1160
193
0.05
8089
072
1271
0.28
2119
5.10
1.44
1.56
1.73
z93
0.28
2315
899
5.27
947E-‐05
0.00
1369
089
0.06
7471
923
665
0.28
2299
-‐2.08
1.85
1.34
1.72
z95
0.28
2155
269
3.61
692E-‐05
0.00
1795
766
0.09
2698
242
1374
0.28
2109
7.03
1.27
1.58
1.69
z103
0.28
2098
963.75
4E-‐05
0.00
1006
499
0.05
3444
005
1207
0.28
2076
2.12
1.31
1.63
1.87
z107
0.28
2293
551
4.58
359E-‐05
0.00
1048
917
0.04
3971
331
947
0.28
2275
3.35
1.60
1.36
1.59
z110
0.28
1822
943.28
947E-‐05
0.00
1047
126
0.04
8748
737
1587
0.28
1791
0.59
1.15
2.01
2.25
z111
0.28
1537
041
3.52
457E-‐05
0.00
0935
605
0.04
5713
686
1799
0.28
1505
-‐4.77
1.23
2.40
2.74
z118
0.28
1927
345
5.15
658E-‐05
0.00
4899
363
0.28
5768
289
657
0.28
1867
-‐17.56
1.80
2.08
2.66
z120
0.28
2202
721
2.77
052E-‐05
0.00
0435
761
0.02
0583
139
923
0.28
2195
-‐0.02
0.97
1.46
1.78
z121
0.28
2160
909
4.76
079E-‐05
0.00
1074
221
0.05
6052
334
1300
0.28
2135
6.29
1.67
1.54
1.68
z127
0.28
1956
835
2.84
937E-‐05
0.00
0668
167
0.03
1866
129
1655
0.28
1936
7.26
1.00
1.81
1.90
z130
0.28
1527
669
4.42
24E-‐05
0.00
1288
755
0.05
3306
892
1818
0.28
1483
-‐5.10
1.55
2.43
2.77
z131
0.28
2274
738
2.41
434E-‐05
0.00
0673
740.03
4580
835
950
0.28
2263
2.99
0.85
1.37
1.62
z132
0.28
2228
947
3.47
23E-‐05
0.00
0632
878
0.03
2184
909
995
0.28
2217
2.36
1.22
1.43
1.69
z148
0.28
2145
172
2.73
124E-‐05
0.00
0435
722
0.02
1716
483
1103
0.28
2136
1.92
0.96
1.54
1.80
Lu d
ecay
con
stan
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65 x
10-1
1 Sch
erer
et a
l. (2
001)
Chapter 6: An inconvenient truth: Multiple geomagnetic reversals in the Neoproterozoic–Cambrian Alto Paraguay Group, Amazonian Craton, Brazil.This chapter is under review as:McGee, B., Trindade, R.I.F., Collins, A.S. and Tohver, E., Under review. An inconvenient truth: Multiple geomagnetic reversals in the Neoproterozoic–Cambrian Alto Paraguay Group, Amazonian Craton, Brazil. Precambrian Research.
115
Chapter 6 An inconvenient truth: multiple geomagnetic reversals in the Alto Paraguay Group
An inconvenient truth: Multiple geomagnetic reversals in the Neoproterozoic–Cambrian Alto Paraguay Group, Amazonian Craton, Brazil
Ben McGee*a, Ricardo I.F. Trindadeb, Mariana Rossafab, Alan S. Collinsa, Eric Tohverc
*Corresponding author. Tel: +61 8 8303 4971, fax: +61 8 8303 4347, email: [email protected] for Tectonics, Resources and eXploration (TRaX), School of Earth and Environmental Sciences, Mawson Building, The University of Adelaide, SA 5005, AustraliabDepartamento de Geofísica, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Rua do Matão, 1226, 05508-090, São Paulo, BrazilcSchool of Earth and Environment, University of Western Australia, 35 Stirling Highway, Crawley, WA, 6009, Australia
A B S T R A C T
We present new palaeomagnetic data from the siliciclastic Alto Paraguay Group (northern Paraguay Belt, Brazil) that overlies Marinoan-aged glacial diamictites and cap carbonates of the SE Amazonian craton. The sandstones and mudstones of the Raizama, Sepotuba and Diamantino formations preserve a dual polarity palaeomagnetic direction (Component A) that is similar to that reported from the underlying cap carbonate rocks. Given the large duration of time between these deposits, a negative fold test, and their similarity to the Mesozoic-to-present day field direction, we interpret these results to represent a secondary magnetisation, likely acquired during regional emplacement of Jurassic basalt. This finding is significant because results from the cap carbonate have been used to suggest Amazonia was at low latitudes during the Ediacaran, which has implications for the snowball earth hypothesis and the tectonic evolution of the Paraguay Belt. A second palaeomagnetic direction (component B) is present in only four samples of the Diamantino Formation, but does not correspond to any known or expected direction for the Amazon craton. A third palaeomagnetic direction (component C) isolated from the E-W trending portion of the curved Paraguay Belt is similar to a late-Cambrian overprint observed in the carbonates of the underlying Araras Group. The presence of this dual polarity, post-folding result in the Raizama Formation indicates that the Raizama Formation had already been deposited, folded, and remagnetised prior to oroclinal bending of the Paraguay Belt.
Keywords:
Gondwana
Palaeomagnetism
Paraguay Belt
snowball Earth
Alto Paraguay Group
1. Introduction
Since its development, palaeomagnetism has provided us with information about Earth’s ancient magnetic field stored in rocks, enabling us to track the movement of tectonic plates and giving an understanding of Earth’s
palaeogeography. The global reference frame provided by the ancient geomagnetic field has been used in tracking the assembly and break-up of supercontinents such as Gondwana (e.g. Collins and Pisarevsky, 2005; Tohver et al., 2006). In addition to their role in developing the theory of plate tectonics, more recently
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palaeomagnetic results have been used as part of the snowball earth hypothesis to suggest that low latitude continents and their associated glacial deposits provide evidence that the earth was completely covered in ice at least twice during the Neoproterozoic (Hoffman et al., 1998). The putative severity that these glaciations were so vast rests almost entirely on palaeomagnetic data, notably the existence of low-latitude, sea-level glacial deposits (Hoffman and Li, 2009). The hypothesis is that if ice sheets occurred at sea level in the warmest regions of the surface ocean (i.e. the equator), then higher latitudes and topography must have also been covered in ice.
To date, there are only a few palaeomagnetic results that locate Marinoan glacial deposits at low-latitudes. Palaeomagnetic data from the Elatina Formation in South Australia define a palaeopole and indicate that grounded ice near sea-level occurred in equatorial palaeolatitudes (Schmidt and Williams, 1995; Sohl et al., 1999). Evidence for glacial rocks at the palaeoequator are found in the Huqf Supergroup in Oman where glacial tillites and their associated cap carbonates have been found to be deposited within the tropics (Kilner et al., 2005). A third piece of evidence for low-latitude glaciation has been presented from the cap carbonate of the glaciogenic Puga Formation in Brazil (Trindade et al., 2003). This work suggested that the presence of stratabound reversal stratigraphy and high unblocking temperatures in the Araras Group carbonates meant that the observed magnetic remanence was primary, despite the close proximity of the observed direction to the present day field (PDF).
Here, we report new palaeomagnetic data from above the Araras Group, in the siliciclastic Alto Paraguay Group. We define three components from these data and show that the most well defined direction is similar to the pole presented by (Trindade et al., 2003) suggesting that this magnetisation is not ancient but more likely Jurassic in age. The other components are also presented and discussed in the context of the evolving Paraguay orocline.
2. Geological Setting
The northern Paraguay Belt, the focus of this work, is an oroclinal orogeny that is part of a large suture zone involving the Pampean Belt to the south and Araguiaia Belt to the north (Trindade et al., 2006). To the north of the belt lies the south-eastern margin of the Amazon Craton, but basement rocks do not outcrop in the belt itself. The belt is composed of folded and weakly metamorphosed (lowest greenschist facies) Neoproterozoic passive margin sedimentary strata, which occurred as the result of collision between Amazonia and proto-Gondwana. The siliciclastic rocks of the upper Alto Paraguay Group that were deposited in the foreland of the Paraguay Orogen record the final stages of this collision (Bandeira et al., 2011). This occurred during the Cambrian Period (Trindade et al., 2003), with the end of orogenesis marked by the intrusion of the post-tectonic granites into the base of the strata at 518 Ma (McGee et al., 2012). Palaeozoic sedimentary deposits of the Paraná Basin to the SW of the study region mark a period of intracratonic subsidence that lasted until the early Mesozoic. Early Jurassic tholeiitic basalt flows are also present, Tapirapuã Formation is intrusive into the north-western part of the belt (Figure 1a) and the Anari Formation lies some 400 km to the northwest (Monteslauar et al., 1994).
The strata comprising the northern Paraguay Belt are divided into three groups. The older pelites, diamictites and siliciclastics of the roughly 4–6 km thick Cuiabá Group lie in the core of the orogen (Barros et al., 1982). The relationship between the Cuiabá Group and glacial diamictites of the Puga Formation is currently poorly established, due to non-exposure of the contact. Consequently the two formations have been interpreted as either correlative, representing lateral facies variations along the continental slope (Alvarenga et al., 2009) or as unconformable (Nogueira et al., 2007). A maximum depositional age of 706 Ma for the Puga Formation is based on U-Pb SHRIMP ages from the Puga diamictite from the southern Paraguay Belt (Babinski et al., In press).
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Fig. 1. (a) Geological map showing lithostratigraphic relationships within the northern Paraguay Belt, modified from CPRM Cuiabá 1:1000000 map sheet (Barros et al., 1982). Formation codes correspond to those used in the CPRM map sheet. (b) Schematic stratigraphic section for the northern Paraguay Belt showing sample locations. Note: thicknesses of units are not to scale.
A NOTE:
This figure/table/image has been removed to comply with copyright regulations. It is included in the print copy of the thesis held by the University of Adelaide Library.
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Chapter 6 An inconvenient truth: multiple geomagnetic reversals in the Alto Paraguay Group
A thick package of carbonates belonging to the Araras Group overlie the Puga Formation and are subdivided into four formations. The basal cap carbonate, the Mirrasol d’Oeste Formation, is followed by limestone and shale of the Guia Formation, dolostone and dolomite breccias of the Serra do Quilombo Formation and dolostone, chert, sandstone and lime mudstone of the Nobres Formation. The base of the Araras Group is constrained by Pb-Pb whole-rock isochron ages of 627 ± 30 Ma (Babinski et al., 2006) and 633 ± 25 Ma (Alvarenga et al., 2009), consistent with chemostratigraphic correlation to the post Marinoan glaciation (Nogueira et al., 2007).
The glacially influenced Serra Azul diamictite rests unconformably on top of the Araras Group carbonates and is inferred to be related to the Gaskiers glaciation (Alvarenga et al., 2007; McGee et al., Under review). Mudstones overlying the Serra Azul diamictite signify a postglacial transgression and the coarsening upward nature of this sequence indicates a progressive filling of the basin with a gradual transition to the overlying siliciclastics of the Alto Paraguay Group. The Raizama Formation is composed of siltstones, sandstones and pebble conglomerates deposited on a storm and tidally influenced platform. Marine deposition ceased shortly after this and final deposition within the restricted Diamantino lake is recorded by red shales, siltstones and arkoses of the Diamantino Formation (Bandeira et al., 2011).
The age of the Alto Paraguay Group is poorly constrained due to the lack of volcanic layering, however, a recently reported maximum depositional age from prograding deltaic lobes of the Diamantino indicated they formed after 541 Ma (Bandeira et al., 2011). No fossils or trace fossils have been reported from the Alto Paraguay Belt. While few direct age constraints are available for the Paraguay Belt, the maximum depositional age of the Puga diamictite is 706 ± 9 Ma based on the age of the youngest detrital zircon (Babinski et al., In press).This result precludes it from being Sturtian in age and suggests that it is a correlative of the ~635 Ma Marinoan glaciation. This conclusion is supported by
both the δ13C (5.0‰) and the 87Sr/86Sr (0.7080) ratios from carbonates directly overlying the diamictites (Nogueira et al., 2003). Available radiometric ages for the Alto Paraguay Group include a Rb-Sr clay age of 569 ± 20 Ma from the Sepotuba and Diamantino formations (Cordani et al., 1978) and a detrital U-Pb age for the upper Diamantino Formation of 541 ± 7 Ma (Bandeira et al., 2011).
Previous palaeomagnetic work in the Paraguay Belt has focused on the carbonates overlying the Marinoan Puga diamictite (Tohver et al., 2010; Trindade et al., 2003). Trindade et al. (2003) provided evidence for multiple geomagnetic reversals in this group and used their results to imply a low-latitude Amazonia at ca. 520 Ma. Tohver et al. (2010) showed that early thrusting in the Paraguay Belt was associated with clay mineral transformations and chemical remagnetisation of carbonates in the Araras Group at ca. 528 Ma. Tohver et al. (2010) also showed that oroclinal bending of the Paraguay Belt was caused by a 90° clockwise rotation of the east-limb some time after 528 Ma.
This curvature results in NNW-SSE structural trends in the south to NNE-SSW and east-west structural trends in the north of the belt (Figure 1a). Structurally, the belt can be divided into two domains; the undeformed to weakly-deformed fringe at the edge of the Amazonian Craton where primary layering is often only gently tilted by 10–20°. The second domain in the core of the orogeny hosts tight regional scale folds and thrusts (Figure 1a). Here, we have divided the belt into three structural sectors; sector 1, the NNE-SSW trending part of the belt, sector 2, the NE-SW trending part of the belt and sector 3, the E-W trending portion of the belt.
3. Methods
Palaeomagnetic samples were collected in the field both as oriented hand samples and Pomeroy drill cores. Sample sites were selected based on their stratigraphic (temporal) position (Figure 1b) within the Alto Paraguay Group and lateral position within the northern Paraguay Belt. Spatial cover of the belt is
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good with data from the southernmost part of the belt to its inflection point and out to the east (Figure 1a). Only sites with fresh rock were sampled. All samples were oriented in the field using a magnetic compass and sun compass. Laboratory work was conducted at the Institute of Geophysics at the University of São Paulo in Brazil. Hand samples were drilled into cores of 2.2 cm diameter and cut to the same length. Drilled core samples were cut to the same length.
The natural remanent magnetism (NRM) for all specimens was subsequently measured using an Agico JR6A Spinner Magnetometer, set to manual mode (4 positions, velocity = 87.7 rev./sec.) to allow for increased sensitivity. This information was used to separate 3 specimens from each site with the highest NRM to conduct a pilot study. Two specimens were thermally demagnetised, in 18 steps, at increments of 100°C, 50°C and 20°C respectively up to 700°C where necessary. The other specimen was demagnetised in 13 steps, at increments of 5−10 mT up to a maximum of 100 mT in an alternating field using an Agico LDA3A demagnetiser in tumbling mode. After each demagnetisation step the direction and intensity of magnetisation was measured on the spinner magnetometer. At the completion of this pilot study these data were used to decide which sites were suitable for AF demagnetisation (i.e. those that completely demagnetised in the AF) and which sites required demagnetising thermally (sites that didn’t demagnetise completely under the AF).
The direction and magnetic intensity of specimens in the second suite of samples were measured using a 2G cryogenic magnetometer. AF demagnetisations were also conducted on this instrument, this time in 25 steps, with intervals of 2−10 mT. The increments for thermal treatment remained the same as in the pilot study.
Data processing and principal component analysis was conducted using Agico’s Remasoft 3.0. Linear segments were chosen from Zijderveld plots and used to calculate vectors for each specimen. The segment corresponding to a stable magnetization was selected whilst concurrently considering the
demagnetisation path on both orthogonal plots and equal area projections.
Thermomagnetic properties were measured with a CS4 apparatus coupled to an Agico Kappabridge KLY-4 in order to characterise the magnetic carriers in the samples. One specimen per site was selected for analysis and magnetic susceptibility was measured in a step-wise fashion in a low temperature domain (-200°C−0°C) and high temperature domain (0°C−700°C) over a period of 60 minutes in an Argon atmosphere.
4. Results
4.1 Demagnetisations
Demagnetisations for the Alto Paraguay Group samples are presented in Figures 2 – 4. The samples generally carry a weak natural remnant magnetisation (NRM) of around 0.5–1 x 10-3 Am-1. 226 of the samples (287 samples from 29 sites) yielded stable magnetisations, with three principal clusters observed. In the following discussion, clusters of similar palaeomagnetic directions are presented together, and these clusters generally correspond to geographic location of the sites.
Demagnetisation of specimens of the Raizama and Sepotuba formations in sector 1 produced 71 stable results. The stable magnetisation is commonly uni-vectorial (Figure 2) and general ranges for the unblocking temperature are typically between 500°C and 580°C. Orthogonal plots generally show tightly clustered, stable demagnetisations despite their low NRM (Figure 2). The resulting directions are predominantly moderately upward plunging to the north or shallowly plunging to the south/south-east (Figure 2). Grouping these results together reveals a single magnetic component that is stable until temperatures of 640 °C (Figure 2).
Specimens from sector 2 of the Raizama and Diamantino formations revealed 73 stable magnetisations. The range of unblocking temperatures is typically 500°C – 600°C or up to 50mT. Both single and bi-vectorial magnetisations were found in specimens from
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Fig. 2. Demagnetisation patterns for Alto Paraguay Group samples from sector 1 that comprise component A. Open and closed circles represent positive and negative directions in stereonets and vertical and horizontal directions in orthogonal plots respectively.
sector 2 (Figure 3 a–c and d–f respectively). The uni-vectorial magnetisations are shallowly northward dipping, upward or downward, and have steady demagnetisation patterns. The bi-vectorial specimens also preserve this shallow, northward dipping component in addition to a high temperature secondary component that is slightly steeper and dips west-northwest. The demagnetisation patterns revealed in the stereograms in Figure 3d–f are characteristic of progressive removal of a magnetic overprint to reveal a more ancient magnetisation.
Specimens from sector 3 belong to the Raizama and Sepotuba formations and produced 82 stable magnetisations. The stable magnetisations are a both uni-vectorial (Figure 4b,c & e) and multi-vectorial (Figure 4a, d & f). Unblocking temperatures are usually high at around 580°C – 680°C and directions are typically tightly clustered in the stereograms until these temperatures are reached (Figure
4). The characteristic directions revealed by these sites are dual polarity, either steep and upward to the northwest and downward to the southeast.
4.2 Magnetic Mineralogy
Despite low susceptibility values for the majority of the Alto Paraguay Group samples, it is still possible to infer information about their mineralogy from thermomagnetic and demagnetisation curves. In the high temperature curves, a number of sites reveal one prominent inflection at around 600°C (Figure 5a & b). After this point, susceptibility values drop significantly to near-zero at around 680°C—the Curie temperature of hematite. The Morin transition at -20°C—indicative of hematite—is observed in a number of the corresponding low temperature curves (e.g. Figure 3a and b). Thermal demagnetisation
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Fig. 3. Demagnetisation patterns for Alto Paraguay Group samples from sector 2 that comprise components A and B (represented by grey rectangles in orthogonal plots). Open and closed circles represent positive and negative directions in stereonets and vertical and horizontal directions in orthogonal plots respectively.
curves presented in Figure 5a and b show that complete removal of the magnetic field from these samples is only achieved after 680°C, confirming hematite as the magnetic carrier in these samples. These specimens correspond to those discussed previously in section 4.1 indicating that hematite is the carrier for the secondary magnetic component in Figure 3d–f.
The AF demagnetisation curve presented in Figure 5c shows a significant decay in intensity from 0−20 mT, typical of the mean destructive field of magnetite. Coupling these observations with the lack of a Morin transition in the low temperature curve but a Curie temperature of 680°C suggests that both magnetite and hematite are the magnetic carriers. A portion of the high temperature curves display non-reversible behaviour (e.g. Figure 5d). In this example the cooling curve in the high
temperature plot exhibits a Curie temperature of 580°C. A subtle Verway transition (-153°C) is observed in the low temperature curve and the complete loss of magnetic intensity by 100°C indicates the growth of secondary magnetite during heating.
4.3 Magnetic Components
Characteristic directions for each sector were selected and are represented in Figure 6 with the corresponding data in Table 1. 120 of the 226 stable samples were used to define three magnetic components.
The combination of directions from sector 1 and sector 2 (Figure 6a) produce a dual polarity component (A), with an upward directed cluster at -14/350 and a downward cluster at 20/164. These data fail the fold test (Figure 7) indicating component A is an overprint
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younger than the regional folding and rotation of the Paraguay Belt. Sector 2 data also contain a weakly defined, high temperature hematite component (B) at 17/309 (Figure 6b). These data also fail the fold test (Figure 7), owing to the small sample population defining this component. Sector 3 defines a steep dual-polarity component C (Figure 6c), dipping upward at 85/300 and downward at 75/160. While the tilt corrected data are more tightly clustered, signified by a higher kappa value after 100% tilt correction (Figure 7), they do not fall within the range of which kappa is statistically significant at the 95% confidence level and thus produce a negative test. This indicates that magnetisation of component C was most likely acquired after tilting.
In addition to the above precision tests for components A–C, stability tests were carried out on components A and C by determining if the mean of their normal and reversed-
polarity constituents were non-unique. Figure 8 shows the results of these reversal tests with the normal polarity analyses plotted against the transposed reversed-polarity analyses and their means represented by large black and grey circles respectively, surrounded by their α95 circles. Component A (Figure 8a) passes the reversal test for both the in situ and tilt corrected data—since the means are not distinct at the 5% significance level—indicating that the two means in each stereonet represent the same population. Component B fails the reversal test for the in situ data but gives a positive reversal test for the tilt corrected data (Figure 8b).
5. Discussion
The negative fold tests outlined in Figure 7 indicate that all of the palaeomagnetic components defined here were obtained
Fig. 4. Demagnetisation patterns for Alto Paraguay Group samples from sector 3 that comprise component C. Negative and positive vectors are represented by open and closed circles respectively.
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Fig. 5. Selected thermomagnetic curves (high and low temperature domains) and demagnetisation curves for Alto Paraguay Group samples, showing predominance of hematite. In high temperature plots, heating and cooling curves are represented in black and grey respectively.
prior to folding within the northern Paraguay Belt. Component A (Figure 6a), which is defined from sectors 1 and 2, is similar to the Mesozoic-to-present day field directions shown in Figure 9. This component is also similar to the ‘component A’ presented by Trindade et al. 2003 from the cap carbonate of the Puga Formation. Based upon the available ages for this sequence and given that the results presented here from the Alto Paraguay Group lie stratigraphically at least 1500 m above the cap carbonates of the Puga Formation,
we estimate a maximum time gap of ~70 Ma between these components. Two main possibilities exist to explain these observed similarities, the first being that the position of the Amazon Craton was the same at the time of deposition of both the cap carbonate to the Puga Formation and the overlying Alto Paraguay Group sediments. This could either be through lack of movement of the craton or through a drift history that re-located it into a similar position.
The second possibility, the one we find more
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Chapter 6 An inconvenient truth: multiple geomagnetic reversals in the Alto Paraguay Group
Fig. 6. Characteristic remanent directions from individual specimens defined by principal component analysis, both in situ (left) and tilt cor-rected (right). Small open and closed circles represent negative and positive vectors respectively, black and grey circles are from sector 1 and 2 respectively. (a) Component A from sector 1 and 2. (b) Component B from sector 2. (c) Component C from sector 3.
Fig. 7. Fold tests for Alto Paraguay Group components. Open squares, triangles and circles represent components A, B and C respectively.
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Chapter 6 An inconvenient truth: multiple geomagnetic reversals in the Alto Paraguay Group
Fig. 8. Reversal tests for components (a) A and (b) C. Negative and positive vectors are represented by open and closed circles respectively.
likely given the large duration of time between these deposits, a negative fold test, and their similarity to the Mesozoic-to-present day field directions, is that these results represent a secondary magnetisation. We propose that this magnetisation was acquired during regional emplacement of the Tapirapuã tholeiitic basalt at around 197 Ma, which intrudes into the north-western margin of the northern Paraguay Belt (Figure 1a). A Jurassic age for remenance acquisition is consistent with the observation of multiple reversals, given the large number of polarity shifts during this geological period (Ogg et al., 2008).
The observation of multiple polarity reversals in the Puga Formation cap carbonate was used as evidence by Trindade et al. (2003) to suggest that magnetisation was primary and that their occurrence over ~20 m of the cap carbonate suggested a large time interval for deposition, much larger than that hypothesised by the rapid deglaciation model of Hoffman et al. (1998). The apparent stratabound reversals of Trindade et al. (2003) could well have
obtained this pattern of magnetisation during the Jurassic given the chances for multiple overprints by the changing magnetic field.
The pole produced from the results of Trindade et al. (2003) has been used as evidence to suggest that Amazonia and the related glaciogenic deposits of the Puga Formation were deposited at low-latitudes. A fundamental requisite of the snowball earth hypothesis is that if glaciers existed at low latitudes they would produce a runaway albedo feedback effect that would see the whole world covered in ice (Hoffman et al., 1998). Our results suggest that the data presented by Trindade et al. (2003) should be used with caution when assigning a low latitude position for the Amazon Craton.
Component B is certainly resolvable in some samples of the Raizama and Diamantino from sector 2. However, at this stage it is poorly resolved with too few data points to be regarded as an accurate recorder of the geomagnetic field. In addition, its failure of a fold test leads us to decline from draw
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Chapter 6 An inconvenient truth: multiple geomagnetic reversals in the Alto Paraguay Group
conclusions about its meaning.The final component resolved here,
component C from sector 3, also produced a negative fold test, and as such we interpret that magnetisation was acquired after regional folding within the northern Paraguay Belt. However, the reverse component represented by these data are at ~90° to the 525 Ma reference direction presented by Tohver et al. (2010). Tohver et al. (2010) used their results from the underlying Araras Group to show that oroclinal bending of the Paraguay Belt was caused by a 90° clockwise rotation of the east-limb some time after 528 Ma. Our results corroborate these data and as such, we interpret that the Raizama Formation in sector 3 was deposited, folded and remagnetised with the Araras Group. Subsequently this whole package was rotated about a vertical axis by ~90° producing the presently observed orocline, most likely in response to the shape of the Amazon Craton. Due to a lack of fresh outcrop it was not possible to sample the Diamantino Formation in sector 3, which may have facilitated an investigation of the timing of deposition and rotation of the Diamantino Formation. Recent stratigraphic work by McGee et al. 2012 does, however, indicate that the Alto Paraguay Group is a continuous sequence with no obvious unconformities. This observation suggests that the Diamantino was also deposited, folded, magnetised and
rotated with the Araras Group.
6. Conclusions
This study presents new palaeomagnetic data from siliciclastic rocks of Alto Paraguay Group, overlying Marinoan cap carbonates, from the northern Paraguay Belt in Brazil. Component A, which fails the fold test and is nearly identical to the PDF and other Mesozoic-to-present day directions is also similar to the directions provided by Trindade et al. (2003). The pole of Trindade et al. (2003) has been used to suggest Amazonia was at low latitudes at the time of the Puga (Marinoan) glaciation and also has implications for the timing of Gondwana amalgamation (Trindade et al., 2006). Our results indicate that care should be taken when interpreting this magnetisation as primary, and thus the significance of the associated pole, given that we obtained similar results much higher in the stratigraphy of the Alto Paraguay Group. We advocate a much younger age for remagnetisation during the Jurassic, a reasonable conclusion given to the presence of a large tholeiitic basaltic intrusion into the north-west margin of the northern Paraguay Belt.
The other important conclusion of this work is that the results from the Raizama Formation in the east-limb of the belt (sector 3) corroborate with the post-folding, 90° rotation of the east limb of the northern Paraguay Belt found by Tohver et al. (2011).
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Chapter 7: Key Outcomes and Future Research
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The following discussion outlines the key findings of this study, establishing the current field of knowl-edge regarding the break-up of Rodinia, the subsequent amalgamation of the supercontinent Gondwana and the glacial events of the time. It also outlines the potential future directions for further research within the context of this thesis.
The rift-related, Cryogenian-aged Toekems Sub-basin provides a unique exposure of the Nauuwpoort and Chuos formations and insight into the inter-relationship between Rodinian rifting and glaciation. The 763 Ma pegmatite cross-cutting the basal breccia adds to the suite of ages constraining initial rifting and open-ing of the basin. The overlying package of dominantly siliciclastic marine sediments that fills the Toekems Sub-basin is most likely equivalent to the Chuos Formation, based on apparent glacial influence, the pres-ence of iron-formation and stratigraphic position beneath the Rasthof cap carbonate. This correlation im-plies that the Naauwpoort Formation and Ugab Subgroup, are almost completely absent in this section, and hence that the unconformity spans a significant amount of time. Our new data provide evidence for multi-phase, middle Neoproterozoic extension on the south-western margin of the Congo Craton. Future studies in this area should focus on dating the felsic intrusives in the region to better constrain rifting and sedimentation within these basins.
The key outcome of chapter 2 is placing a minimum age constraint on the cessation of orogenesis within the northern Paraguay Belt. The Paraguay Belt in central South America is part of a larger chain of orogenic belts, including the Araguaia Belt to the northeast and potentially the Pampean Belt to the south that are interpreted amongst the youngest of the Gondwana amalgamation orogens. Placing a minimum age con-straint on this deformation is achieved via dating the post-orogenic São Vicente Granite, which crops out in the northern Paraguay Belt and cuts the basal unit of the deformed and metamorphosed sediments of the belt. Based on LA-ICPMS dating of more than 100 zircons from three separate samples we interpret a robust crystallisation age for the São Vicente batholith at 518 ± 4 Ma. This age constrains the termination of deformation within the Paraguay Belt and the final accretion of the supercontinent Gondwana. Dating crystallisation of this important intrusion proved challenging due to the presence of considerable common-Pb. Future studies should focus on removing this uncertainty from the age of this intrusive.
Chapter 3 of this thesis outlines the current field of knowledge for glacial deposits that are potentially of Gaskiers age (ca. 580 Ma) using the northern Paraguay Belt as a locality to document new evidence for glaciation at this time. Based on the observations in this chapter we infer that the canyon found at the São Sebastião section was most likely formed by a combination glacioeustatic drawdown and isostatic uplift due to glacial erosion. Given current geochronologic constraints and its stratigraphic location it appears that this glaciation is mid-Ediacaran in age and most likely associated with the ~582 Ma Gaskiers Forma-tion glaciation. Without suggesting that the Gaskiers glaciation was global in extent, the geological record certainly indicates a global record of glaciation and potentially related glacially incised valleys. In order to illu-minate our knowledge of this period, future work should focus on increasing the palaeomagnetic database for cratonic blocks at this time to gain a better understanding of their palaeogeography. A better idea of the stratigraphic relationships between these glacial deposits would also be beneficial, which could be made possible by an increased number of geochronological, chemo-stratigraphic and bio-stratigraphic studies.
In addition to elaborating on the sedimentology and stratigraphy of the previous chapter, chapter 4 also provides the first age constraints on the glacial sediments of the northern Parguay Belt, the Serra Azul Formation. The key finding is that these ages, when considered with other data, that the Serra Azul Formation developed in a mid-Ediacaran glaciation consistent with that expressed in the Gakiers Forma-tion of Newfoundland, Canada. Another key outcome is the presentation of a tectonic model based the new ages and sedimentological work showing the transition from a marine passive margin environment to a compressional setting where the Paraguay Belt developed as a peripheral bulge in the lithosphere of the Amazonian Craton.
Chapter 5 provides additional ages constraints on the northern Paraguay Belt, presenting the first com-prehensive detrital zircon study from the region. The ages from the top of this sequence, the Diamantino Formation, indicate final sedimentation in the Paraguay Belt began no earlier than 527 Ma. Based on the integrated U-Pb and Hf isotope data of detrital zircons presented here, potential sources for these sedi-ments are consistent with a predominantly Amazonian source until the early-Neoproterozoic at which point the signal becomes significantly more evolved and influence from the Paranapanema, and Goiás Massif to the east are inferred. Available evidence from Chapters 4 and 5 suggests that final sedimentation, defor-mation and metamorphism in the Paraguay Belt occurred between 540 and 510 Ma. Despite providing an excellent regional overview of the provenance of the sediments within the northern Paraguay Belt, a further study could certainly focus on finding volcanic horizons to provide more concise age constraints on sedi-mentation and glaciation within the belt.
The final chapter of this thesis presents new palaeomagnetic data from siliciclastic rocks of Alto Para-
Key Findings
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guay Group, overlying Marinoan cap carbonates. Our results indicate that care should be taken when inter-preting magnetisation of rocks in this region as primary, given that we obtained similar results to an earlier study much lower in the stratigraphy of the Alto Paraguay Group. We advocate a much younger age for remagnetisation during the Jurassic, a reasonable conclusion given to the presence of a large tholeiitic ba-saltic intrusion into the north-west margin of the northern Paraguay Belt. Future research in this area should focus on placing better constraints on the timing of magnetisation within these rocks.
Chapter 8: AppendixThe U-Pb zircon analyses and data presentation and interpretation were conducted by the PhD candidate and this chapter is published as:
Bandeira, J., McGee, B., Nogueira, A.C.R., Collins, A.S. and Trindade, R.I.F., 2012. Closure of the Neo-proterozoic Clymene Ocean: sedimentary and detrital zircon geochronology evidence from the siliciclastic upper Alto Paraguai Group, northern Paraguay Belt, Brazil. Gondwana Research.
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Chapter 8 Sedimentological and provenance response to the Cambrian closure of the Clymene Ocean
A Bandeira, J., McGee, B., Nogueira, A.C.R., Collins, A.S. & Trindade, R. (2012) Sedimentological and provenance response to Cambrian closure of the Clymene ocean: The upper Alto Paraguai Group, Paraguay Belt, Brazil. Gondwana Research, v. 21(2-3), pp. 323-340
NOTE:
This publication is included on pages 135-152 in the print copy of the thesis held in the University of Adelaide Library.
It is also available online to authorised users at:
http://dx.doi.org/10.1016/j.gr.2011.04.006