FROM CRUSTAL THINNING TO MANTLE EXHUMATION: WHAT …€¦ · Cataclastic breccias of marbles- Aulus...
Transcript of FROM CRUSTAL THINNING TO MANTLE EXHUMATION: WHAT …€¦ · Cataclastic breccias of marbles- Aulus...
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sedimentarybreccias
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upper Aptianlower Albian
middle Albianlower Cenomanian
333 RSCM Peak Temperaturethis study
570 Temperature fromGoldberg and Leyreloup(1990)
Simplified geologic map of the North Pyrenean Hercynian Massifs and peridotite outcrops
P e a k t e m p e r a t u r e s o f t h e H T / L P c r e t a c e o u s m e t a m o r p h i s m i n t h e P y r e n e e s
Clerc Camille1, 2 ; Lagabrielle Y.2 ; Reynaud J.-Y.3 ; Boulvais P.4 ; Bousquet R.4 ; Lahfid A.1, 5 ; Vauchez A.2 ; Mahé S.2, 6
FROM CRUSTAL THINNING TO MANTLE EXHUMATION: WHAT THE PYRENEAN BRECCIA FORMATIONS TELL US ?
Corresponding author: [email protected] Laboratoire de Géologie, CNRS-UMR 8538, Ecole Normale Supérieure, Paris, France; 2 Géosciences Montpellier, Montpellier, France;
3 Muséum national d'Histoire naturelle, Paris and ISTeP Paris, France; 4 Géosciences Rennes, France;5 BRGM / LMA / MIN, Orléans, France; 6 Ecole des Mines, Alès, France
Aude
Agly
Luzenac
St. Barthélémy
C a s t i l l o n
B a r o u s s e
M i l h a s
Trois seigneurs
A r i z e
BessèdeSalvezines
A g l y
Aigue
tte
Boulzane
S y n f o r mB a s A g l y
B o u c h e v i l l e S y n f o r m
A X I A L Z O N E
A X I A L Z O N E
St GaudensLannemezan
TARBES
PAU
St Girons
Pamiers
Foix
Tarascon-sur-Ariège
Quillan
Limoux
PERPIGNAN
Mauléon-Licharre
St JeanPied-de-Port
St Jean-de-Luz
BAYONNE
SAN SEBASTIAN
Orthez
Oloron-Ste Marie
PAMPLONA
Lourdes
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INTRODUCTION: Several formations with various breccia types occur in Mesozoic basins disseminated along the North Pyrenean fault, on the northern flank of the French Pyrenees. Due to their location along the Iberia-Europa plate boundary, the North Pyrenean breccia formations represent complex archives documenting the tectonic and
LOOKING FOR A POSTDOCCenomanianSantonian
sedimentarybreccias
Peridotite upper Cretaceousto Quaternary
Paleozoicbasement
Triassic tolower Aptian
upper Aptianlower Albian
middle Albianlower Cenomanian
References: Goldberg, J.-M., et A.F. Leyreloup. 1990. High temperature-low pressure Cretaceous metamorphism related to crustal thinning (Eastern North Pyrenean Zone, France). Contributions to Mineralogy and Petrology 104, 194–207; * Barbieri, M., U. Masi, & L. Tolomeo. 1979. Stable isotope evidence for a marine origin of ophicalcites from the north-central Apennines (Italy). Marine Geology 30, 193–204; ** Evans, C.A., & M. Baltuck. 1988. Low-Temperature Alteration of Peridotite, Hole 637A. Proceedings of the Ocean Drilling Program, 103 Scientific Results, 235–239; Milliken, K.L., & J.K. Morgan. 1996. Chemical Evidence for Near-Seafloor Precipitation of Cacite in Serpentinites (Site 897) and Serpentinite Breccias (Site 899), Iberia Abyssal Plain. Proceedings of the Ocean Drilling Program, 149 Scientific Results, 553–558; Skelton, Alasdair D.L., and J. W. Valley. 2000. The relative timing of serpentinisation and mantle exhumation at the ocean-continent transition, Iberia: constraints from oxygen isotopes. Earth and Planetary Science Letters 178, 327–338; *** Weissert, Helmut, & Daniel Bernoulli. 1984. Oxygen isotope composition of calcite in Alpine ophicarbonates: a hydro-thermal or Alpine metamorphic signal ? Eclogae geol. Helv. 77, 29–43; Barrett, Timothy J., & H. Friedrichsen. 1989. Stable isotopic composition of atypical ophiolitic rocks from east Liguria, Italy. Chemical Geology: Isotope Geoscience section 80, 71–84; Demeny, A., T. Vennemann, & F. Koller. 2007. Stable isotope compositions of the Penninic ophiolites of the Köszeg-Rechnitz series. Central European Geology 50, 29–46; Früh-Green, G., H. Weissert, & D. Bernoulli. 1990. A multiple fluid history recorded in Alpine ophiolites. Journal of the Geological Society 147, 959–970.
Alpine medium -T ophicalcites*(seawater or metamorphic �uids related)
Iberian marginlow-Temperature ophicalcites
(seawater related)**
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δ18O
veinsmatrixesclasts
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rn P
yrenees
M oncaup
Moncaup
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Ophicalcites fromlitterature:
This study:
Ophicalcites:Agly breccias
F o l d
Semi-ductile syn-metamorphic breccias: The boudinage of silicic or dolomitic beds is the expression of rheologic heterogeneities during the ductile stretching of the meso-zoic cover.
Cataclastic breccias and gouges: The clasts are barely displaced and they display a relatively monogenetic character. These tectonic breccias result from the disruption of the material under cooling conditions. The cata-clastic intervals are mainly hosted by the Triassic and Liassic weaker levels.
Anhydrite vein
Peridotite
Sapphirine bearing
sandstone
Anh
ydrit
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in
Decoupling along the weaker evapo-ritic levels triggers a juxtaposition of the pre-rift sediments directly on the exhumed mantle. We re-interpret the sapphirine bearing sandstones lying around the eastern Pyrenean perido-tites as remnants of these Triassic evaporites transformed by contact metamorphism with the uprising peri-dotites and lower crustal units.
Hydraulic-tectonic breccias: Mid-Cretaceous stretching of the continental crust is accompanied by circulations of hot fluids. These fluids are responsible for allochemical metamorphism, metasomatic reactions and hydrothermalism.
Strike-slip Extension N
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Polymictic sedimentary breccias: Their composition is dominated by clasts of Mesozoic metasediments. Locally, close to subcontinental mantle bodies, the sedimentary breccias include numerous clasts of
ultramafic and/or crustal basement rocks. Such breccias are the witnesses of the disruption and c l a s t i c sedimentation of the sedimentary cover in a context of hyper-extended crust and mantle exhumation.
Stable isotope composition of some Pyrenean breccias and ophicalcites
Syn-metamorphic extensional and/or gravity slidingof pre-rift mesozoic cover on unroofedUB basement
- Tearing of Allochtonous carbonates and UB basement exhumation- Chaotic sedimentation inbetween the individualizing rafts and locally over the mesozoic rafts.- Sliding rafts overthrusting breccia 1- Breccia 2: UB clasts + clasts of mesozoic metasediments + clasts of breccia 1
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Triassic-Liassic evaporitesUB basement Lower crust
breccia 1 breccia 1
olistostrombreccia 2
olistostrombreccia 2
U p l i f t
Parallel carbonate veining in mantle Rock - Urdach
Hydraulic fracturation in mesozoic marbles - Agly
Cataclastic breccias and gouges - Agly
Cataclastic breccias of marbles- Aulus trough
Cataclastic breccias of peridotite - Aulus trough
Polimictic sedimentry breccias - Agly
Ophicalcite - Lherzmarble-peridotite bearing sedimentary breccias- Lherz
The Pyrenean ophicalcites and breccias are displaced toward low d18O values with respect to typicalmarines ones. This could be the sign of their formation in a continental lacustrine environment.
S0
sedimentary evolution of the Pyrenean realm during the Aptian-Albian period. In particular, the North Pyrenean breccia formations have recorded the main stages of crustal thinning, continental break-up and mantle exhumation, which occurred along the North Pyrenean Zone (NPZ).