ing paleontologic, microstructural kinematic analysis, andargon-40/argon-39 and uranium! lead geochronologic inves-tigations will constrain more closely the timing and kinemat-ics of this deformational event. If deformation resulted fromthe Ross Orogeny as we suspect, then the structural history ofthe Ellsworth Mountains is much more similar to that of theTransantarctic Mountains than previously proposed.

This research was supported by National Science Foun-dation grants OPP 92-20395 and OPP 93-12040.

References

Craddock, C. 1983. The East Antarctica-West Antarctic boundarybetween the ice shelves: A review. In R.L. Oliver, P.R. James, andJ.B. Jago (Eds.), Antarctic earth science. New York: Cambridge Uni-versity Press.

Craddock, C., G.F. Webers, R.H. Rutford, K.B. Sporli, and J.J. Ander-son. 1986. Geologic map of the Ellsworth Mountains, Antarctica.Geological Society ofAmerica, Map and Chart Series, MC-57.

Goldstrand, P.M., P.G. Fitzgerald, T.F. Redfield, E. Stump, and C.Hobbs. 1994. Stratigraphic evidence for the Ross orogeny in theEllsworth Mountains, West Antarctica: Implication for the evolutionof the paleo-Pacific margin of Gondwana. Geology, 22(5), 427-430.

Jago, J.B., and G.F. Webers. 1992. Middle Cambrian trilobites from theEllsworth Mountains, West Antarctica. In G.F. Webers, C. Crad-dock, and J.F. Spettstoesser (Eds.), Geology and paleontology of theEllsworth Mountains, WestAntarctjca (Memoir 170). Boulder, Col-orado: Geological Society of America.

Shergold, J.H., and G.F. Webers. 1992. Late Dresbachian (Idamean)and other trilobite faunas from the Heritage Range, EllsworthMountains, West Antarctica. In G.F. Webers, C. Craddock, and J.F.

Spettstoesser (Eds.), Geology and paleontology of the EllsworthMountains, West Antarctica (Memoir 170). Boulder, Colorado:Geological Society of America.

Sporli, K.B. 1992. Stratigraphy of the Crashsite Group, EllsworthMountains, West Antarctica. In G.F. Webers, C. Craddock, and J.F.Spettstoesser (Eds.), Geology and paleontology of the EllsworthMountains, West Antarctica (Memoir 170). Boulder, Colorado:Geological Society of America.

Sporli, K.B., and C. Craddock. 1992. Structure of the Heritage Range,Ellsworth Mountains, West Antarctica. In G.F. Webers, C. Crad-dock, and J.F. Spettstoesser (Eds.), Geology and paleontology of theEllsworth Mountains, WestAntarctica (Memoir 170). Boulder, Col-orado: Geological Society of America.

Vennum, W.R., P. Gizycki, V.V. Samsonov, A.G. Markovich, and R.J.Pankhurst. 1992. Igneous Petrology and Geochemistry of thesouthern Heritage Range, Ellsworth Mountains, West Antarctica.In G.F. Webers, C. Craddock, and J.F. Spettstoesser (Eds.), Geologyand paleontology of the Ellsworth Mountains, West Antarctica(Memoir 170). Boulder, Colorado: Geological Society of America.

Webers, G.F., R.L. Bauer, J.M. Anderson, W. Buggisch, R.W. Ojakan-gas, and K.B. Sporli. 1992. In G.F. Webers, C. Craddock, and J.F.Spettstoesser (eds.), Geology and paleontology of the EllsworthMountains, West Antarctica (Memoir 170). Boulder, Colorado:Geological Society of America.

Webers, G.F., C. Craddock, and J.F. Splettstoesser. 1992. Geologic his-tory of the Ellsworth Mountains, West Antarctica. In G.F. Webers,C. Craddock, and J.F. Splettstoesser (eds.), Geology and paleontol-ogy of the Ellsworth Mountains, West Antarctica (Memoir 170).Boulder, Colorado: Geological Society of America.

Webers, G.F., and K.B. Sporli. 1983. Palaeontological and stratigraphicinvestigations in the Ellsworth Mountains, West Antarctica. In R.L.Oliver, P.R. James, and J.B. Jago (Eds.) Antarctic earth science. NewYork: Cambridge University Press, New York.

Geologic investigations in the Shackleton Range and CoatsLand nunataks, Antarctica

IAN W.D. DALZIEL, MARK A. HELPER, FREDERICK E. HUTSON, and STEPHEN W. GRIMES, Department of Geological Sciencesand Institute for Geophysics, University of Texas, Austin, Texas 78712

Recent global plate reconstructions for the Neoproterozoic(Daiziel 1991; Hoffman 1991; Moores 1991) suggest that

prior to the latest Precambrian to Cambrian amalgamation ofGondwana, the east antarctic craton was the core of an earliersupercontinent, Rondinia, whose break-up gave rise to NorthAmerica. Our research tests this hypothesis by comparing thePrecambrian geology of crustal provinces in North Americaand East Antarctica that the plate reconstructions suggestwere once contiguous. The reconstructions start from thepremise that two, distinct, Precambrian crustal provinces ofthe southwestern United States, the 1.8-1.6 billion-year-oldYavapai-Mazatzal and the 1.3-1.0 billion-year-old Grenvilleorogens, have equivalents in the Weddell Sea region of the eastantarctic craton. Although previous work by British, German,and Russian geologists (cited below) has identified rocks of theformer age range in the Shackleton Range and of the latter innunataks along the Weddell Sea coast in Coats Land (Bertraband Littlewood Nunataks), existing data are insufficient to test

the hypothesis thoroughly. To facilitate a more detailed com-parison, we spent 6 weeks examining and sampling the rocksof these regions. A major goal of the work at both locations wasthe collection of well-characterized suites of samples suitablefor petrologic, isotopic, and paleomagnetic study.

Fieldwork during the 1993-1994 field season was con-ducted from an LC-130-placed tent camp on Recovery Glac-ier, approximately 3 kilometers south of Watts Needle in theRead Mountains of the Shackleton Range (figure). The fieldparty consisted of Ian W.D. Dalziel, Mark A. Helper, FrederickE. Hutson, and Stephen W. Grimes and mountaineers AndyHarris and John Roberts. The camp was supported for 10 daysearly in the season by Twin Otter, which provided transport tothe Coats Land nunataks and allowed 5 days of reconnais-sance work in the Shackleton Range in areas remote from thecamp. These included reconnaissance study and sampling ofsites near the eastern end of the Pioneers Escarpment and thenorthern side of the Read Mountains, a site in the central Her-

ANTARCTIC JOURNAL - REVIEW 19944

C LAG 1amMSRCOATS

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READ M 0 I'

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FILCHNERICESHELF

FUCHSDOME

Generalized outcrop map of the Shackleton Range (asterisk shows location of base camp) and its geographic setting (inset, with area of mainmap outlined). BI—Berkner Island; FIS—Filchner Ice Shelf; HM—Herbert Mountains; LBN—Littlewood and Bertrab Nunataks; MG—MountGass; MP—Mount Provender; MS—Mount Sheffield; MW—Mount Wegener; OH—Otter Highlands; PE—Pioneers Escarpment; SB—Stephen-son Bastion; SR—Shackleton Range; WN—Watts Needle; LGN—La Grange Nunataks.

bert Mountains, and sites at the northern ends of the Otterand Haskard Highlands and at Mount Sheffield in the LaGrange Nunataks. Fieldwork during the remainder of the sea-son was by Ski-Doo and sledge-supported ground traversesfrom the Recovery Glacier camp. Ancillary camps establishedduring extended trips included a temporary camp nearMount Wegener in the Read Mountains and a succession oftemporary camps established during a 2-week traverse to theLa Grange Nunataks, Haskard Highlands, and StephensonBastion.

Prior work on the Grenville-age igneous rocks of theBertrab and Littlewood Nunataks (Eastin and Faure 1971;Marsh and Thomson 1984) suggests that these rocks have notbeen affected by a Ross-age (approximately 500 million years)thermal overprint and, thus, that they may preserve a primarymagnetization. Comparison with extensive North Americanpaleomagnetic reference data for the same time period could,thus, provide a test of the proposed reconstructions. Toexamine this possibility, we collected hand specimens andapproximately 90 oriented rock cores of granophyre and rhy-olite from both groups of nunataks for paleomagnetic analysisand uranium-lead zircon geochronometry. Recently com-pleted paleomagnetic analyses of these samples indicates anexceptionally well-defined primary magnetization that yieldsa pole position that, within the framework of the platerestoration suggested by the Dalziel (1991), is not far from theNorth American Grenville apparent polar wander path for thistime period (see Gose et al. 1994). These data are thus consis-tent with, and lend support to, the suggested Neoproterozoicplate reconstructions.

In the Shackleton Range, a major focus of study was thePaleo- to Mesoproterozoic basement gneisses and granitoidsof the Read Mountains and their Neoproterozoic to LowerCambrian sedimentary cover (Clarkson 1982; Marsh 1983a,pp. 190-193; Pankhurst, Marsh, and Clarkson 1983, pp.176-182; Buggisch et al. 1990). Basement rocks in the ReadMountains have previously yielded rubidium-strontiumwhole-rock ages within the range of those of the Yavapai-Mazatzai province in the southwestern United States and,although in part at higher grade, appear lithologically similar.The fabric of the gneisses throughout the Read Mountains isdominated by a steeply north-dipping mylonitic foliationwith kinematic indicators consistently indicative of a reverseshear sense. This fabric least affects migmatites in the north-ernmost exposures and is most strongly developed in ortho-and paragneisses in central portions of the range. The fabric islocally cut by at least two generations of shallow to steep brit-tie faults and by discordant felsic and mafic dikes and veins.Attitudes of these features were measured throughout therange and samples of basement units representing the spec-trum of cross-cutting relations and compositions were col-lected for uranium-lead geochronometry and neodymium,strontium, and lead isotopic characterization.

The sedimentary cover sequence of the Read Mountainsincludes the Neoproterozoic Watts Needle Formation. TheWatts Needle Formation rests depositionally on Read Moun-tain basement and, at two localities along the southernmountain front, is not appreciably deformed or metamor-phosed (Clarkson 1984; Buggisch et al. 1990; Paech, Hahne,and Maass 1991). Stratigraphic sections at both of these loca-

ANTARCTIC JOURNAL - REVIEW 19945

tions were measured and sampled in detail. Hand specimensand oriented rock cores, keyed to the measured sections, willbe used in an integrated paleomagnetic, stable isotopic andgeochemical study of this sequence in order to establish amore precise age and provide a basis for comparison withsimilar sequences elsewhere. Additional work in the coversequence of the Read Mountains and elsewhere in the Shack-leton Range included• sampling, clast counts, and analysis of sedimentary struc-

tures in the overlying Turnpike Bluff and upper BlaikiockGlacier Groups;

• study of cleavage/ bedding relationships and folding in theTurnpike Bluff Group; and

• measurement of stratigraphic sections and collection oforiented samples for paleomagnetic analysis in the lowerBlaiklock Glacier Group at Mount Gass and Mount Proven-der and in conglomerate of the upper Blaikiock Group atTrey Peaks, Otter Highlands.

In the northern Shackleton Range, tectonically inter-leaved basement and high-grade metamorphic cover of theShackleton Range Metamorphic Complex (Clarkson 1982;Marsh 1983a, pp. 190-193) were examined and sampled dur-ing a 2-week traverse through the La Grange Nunataks andHaskard Highlands. Most of the basement and supracrustalmetamorphic units recognized by Marsh (1983b, 1984) weresampled for uranium-lead geochronometry to establish pro-tolith and metamorphic ages for the complex and to assessthe ages and relationships between fabric formation, thrust-ing, and metamorphism.

This research is supported by National Science Founda-tion grant OPP 91-17996. We wish to thank Antarctic SupportAssociates, U.S. Navy personnel, and Captain Harry Hanlanand his Twin Otter crew of Ken Borek Air Ltd. for their effortsin support of our work. Special thanks go to the personnel ofthe Instituto Antartico Argentino station Belgrano II for theirgracious hospitality, to Werner Buggisch, who kindly provideda geologic map of the Read Mountains resulting from his workwith the German Antarctic program, and to Peter Clarkson ofthe Scientific Committee on Antarctic Research for advice onLC-130 landing sites and logistics.

References

Buggisch, W., G. Kleinschmidt, H. Kreuzer, and S. Krumm. 1990.Stratigraphy, metamorphism and nappe tectonics in the Shackle-ton Range (Antarctica). Geodatische und Geophysikalische Verof-fentlichungen, Reihel, 15, 64-86.

Clarkson, P.D. 1982. Geology of the Shackleton Range I. The Shackle-ton Metamorphic Complex. British Antarctic Survey Bulletin, 51,257-283.

Clarkson, P.D. 1984. Geology of the Shackleton Range II. The Turn-pike Bluff Group. British Antarctic Survey Bulletin, 52, 109-124.

Daiziel, I.W.D. 1991. Pacific margin of Larentia and EastAntarctica/Australia as a conjugate rift pair: Evidence and impli-cations for an Eocambrian supercontinent. Geology, 19(6),598-601.

Eastin, R., and G. Faure. 1971. The age of the Littlewood Volcanics ofCoats Land, Antarctica. Journal of Geology. 79(2), 241-245.

Gose, W.A., I.W.D. Dalziel, M.A. Helper, F. Hutson, and S. Grimes.1994. A positive test of the SWEAT hypothesis: New paleomagneticdata from the "Grenvillian" rocks of Coats Land, Antarctica. Geo-logical Society of America Abstracts with Programs, 26, 503-504.[Abstract]

Hoffman, P.F. 1991. Did the breakout of Laurentia turn Gondwana-land inside out? Science, 252(5011), 1409-1412.

Marsh, P.D. 1983a. The late Precambrian and early Paleozoic historyof the Shackleton Range, Coats Land. In R.L. Oliver, P.R. James,and J.H. Jago (Eds.), Antarctic earth science. Canberra: AustralianAcademy of Science.

Marsh, P.D. 1983b. The stratigraphy and structure of the HaskardHighlands and Otter Highlands of the Shackleton Range. BritishAntarctic Survey Bulletin, 60, 23-43.

Marsh, P.D. 1984. The stratigraphy and structure of the La GrangeNunataks, northern Fuchs Dome and Herbert Mountains of theShackleton Range. British Antarctic Survey Bulletin, 63, 19-40.

Marsh, P.D., and J.W. Thomson. 1984. Location and geology ofnunataks in northwest Coats Land. British Antarctic Survey Bul-letin, 65, 33-39.

Moores, E.M. 1991. The southwest U.S.-East Antarctic (SWEAT) con-nection: A hypothesis. Geology, 19(5), 425-428.

Paech, H.-J., K. Hahne, and I. Maass. 1991. Sedimentological and tec-tonical results on sedimentary rocks outcropping at the southernflank of the Shackleton Range, Antarctica. Zeitschrift für GeologieWissenschaft, 19,159-167.

Pankhurst, R.J., P.D. Marsh, and P.D. Clarkson. 1983. A geochronolog-ical investigation of the Shackleton Range. In R.L. Oliver, P.R.James, and J.H. Jago (Eds.), Antarctic earth science. Canberra: Aus-tralian Academy of Science.

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