to have had only a small effect on uplift of the TransantarcticMountains" (about 100 meters), we suggest that the converseis not necessarily true. If uplift of about 1 kilometers per millionyears since early- or mid-Pliocene did occur, it may in fact havetriggered the most recent advance of the east antarctic ice sheetby a mechanism similar to that proposed for the norther hemi-sphere (winter cooling and increased precipitation caused bymountain uplift culminating in the Plio-Pleistocene ice ages)by Ruddiman and Kutzbach (1989) although their model sug-gested plateau uplift. We suggest a probable synergistic rela-tion between episodic tectonism in the Cenozoic west antarcticrift system and the waxing and waning of the antarctic icesheet (Webb 1990) approximately coincident in time with rift-ing, mountain uplift, and volcanism since Oligocene or earliertime.

References

Behrendt, IC., and A.K. Cooper. 1990. Speculations on the uplift ofthe shoulder escarpment of the Cenozoic West Antarctic rift systemand its relation to Late Cenozoic climate change. In A.K. Cooperand P.N. Webb (Eds.), ANTOSTRAT. (U.S. Geological Survey OpenFile Report 90-309.) U.S. Geological Survey.

Behrendt, J.C., and A.K. Cooper. In press. Evidence of rapid Cenozoicuplift of the shoulder escarpment of the west antarctic rift systemand a speculation of possible climate forcing. Geology.

Cooper, A.K., F.J. Davey, and J.C. Behrendt. 1987. Seismic stratig-raphy and structure of the Victoria Land Basin, western Ross Sea,Antarctica. In A.K. Cooper and F.J. Davey (Eds.), The Antarctic Con-tinental Margin geology and geophysics of the western Ross Sea. Circum-

Pacific Council for Energy and Natural Resources Earth Science Se-ries.

Craddock, C., R.J. Campbell, S.J. Adie, S.J. Carryer, A.B. Ford, H.S.Gair, G.W. Grindley, K. Kizaki, L.L. Lackey, M.G. Laird, T.S. Lau-don, V.R. McGregor, I.R. McLeod, A. Mirsky, D.C. Neethling, R.L.Nichols, P.M. Otway, P.G. Quilty, E.F. Roots, D.L. Schmidt, A.Sturm, T. Tatsumi, D.S. Trail, T. VanAutenboer, F.A. Wade, andG. Warren. 1969. Geologic maps of Antarctica: American GeographicalSociety, Folio 12. New York: American Geographic Society.

Fitzgerald, P.G. 1989. Uplift and formation of Transantarctic Moun-tains—Applications of apatite fission track analysis to tectonic prob-lems. 28th Geological Congress, Abstracts. Washington, D.C.: GeologicalCongress.

LeMasurier, W.E. 1990. Late Cenozoic volcanism on the Antarcticplate—An overview. In W.E. LeMasurier and J.W. Thomson (Eds.),Volcanoes of the Antarctic plate and southern oceans. (Antarctic ResearchSeries, Vol. 48.) Washington, D.C.: American Geophysical Union.

Ruddiman, W.F., and J.E. Kutzbach. 1989. Forcing of the Late Cen-ozoic northern hemisphere climate by plateau uplift in SouthernAsia and the American West. Journal of Geophysical Research, 94(D15),18,409-18,427.

Schmidt, D.L., and P.D. Rowley. 1986. Continental rifting and trans-form faulting along the Jurassic Transantarctic rift, Antarctica. Tec-tonics, 5, 279-291.

Stern, T.A., and U. ten Brink. 1989. Flexural uplift of the TransantarcticMountains. Journal of Geophysical Research, 94, 10,315-10,330.

Tessensohn, F., and G. Woerner. In press. The Ross Sea Rift system(Antarctica)—Structure, evolution, and analogues. In M.R.A.Thomson and J.W. Thomson (Eds.), Proceedings of the Fifth Interna-tional Symposium on Antarctic Earth Science. Cambridge: CambridgeUniversity Press.

Webb, P.N. 1990. The Cenozoic history of Antarctica and its globalimpact. Antarctic Science, 2(1), 3-21.

Geology of metamorphic rocksand granitoids: Ford Rangesof western Marine Byrd Land

D.L. KIMBROUGH

Department of Geological SciencesSan Diego State UniversitySan Diego, California 92182

B.P. LUYENDYK, S.M. RICHARD, and C. SMITH

Institute for Crustal StudiesUniversity of California

Santa Barbara, California 93106

The Ford Ranges provide the most widespread exposuresof pre-Cenozoic (more than 65 million-year-old) rocks in MarieByrd Land (Bradshaw, Andrews, and Field 1983; Adams 1987).Geologic similarities have led previous workers to suggest that

western Marie Byrd Land was adjacent to portions of NewZealand and the Campbell Plateau prior to the late Cretaceousand early Tertiary breakup of the southern margin of Gond-wanaland (e.g., Cooper et al. 1982). The goal of our project isto gain insight into the Mesozoic and Cenozoic tectonics ofWest Antarctica, to explore geologic ties with New Zealand,and to understand the geologic history of separation of NewZealand and the Campbell Plateau from this margin of theGondwanaland supercontinent.

A multidisciplinary investigation of crystalline basement rockin the Ford Ranges of Marie Byrd Land was initiated duringaustral summer 1989-1990. Work was concentrated on the high-grade metamorphic rocks of the Fosdick Mountains and plu-tonic rocks in the adjacent Chester Mountains. The scientificparty consisted of Bruce P. Luyendyk, Stephen M. Richard,and Christine Smith of the University of California at SantaBarbara, and David L. Kimbrough of San Diego State Univer-sity. Thirty-nine days were spent in the field area during De-cember and January with logistic support by VXE-6 LC-130flights. We completed an east-west traverse of the FosdickMountains, with a linking north-south traverse to the ChesterMountains, mapping, making detailed structural observations,and collecting rock samples for paleomagnetic, geochronol-ogic, and petrologic studies (figure).

Three major geologic domains were recognized in the base-

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Generalized map of the Fosdick Mountains and Chester Mountains area adapted from Wade, Cathey, and Oldham (1977, 1978) showingcamps and traverses made during the 1989-1990 field season. BP denotes Birchall Peaks; Ml denotes Mount Iphigene; OG denotes OchsGlacier; MA denotes Mount Avers; ML denotes Mount Lockhart; BB denotes Bird Bluff; GN denotes Griffiths Nunataks; ON denotes O'ConnorNunataks; MR denotes Mount Richardson; MG denotes Mount Getz; NN denotes Neptune Nunataks; MC denotes Mount Corey. (ml denotesmile; km denotes kilometer.)

ment rocks. These are the Fosdick domain, consisting of mig-matitic paragneiss, and orthogneiss; the Chester domain,consisting mostly of granodioritic plutons; and the Mount Coreydomain, consisting of granite plutons. The contacts betweenthese domains are buried under the intervening glaciers, butour observations suggest that a high strain zone separates theFosdick and Chester domains, and that the Mount Corey gran-itoids are younger than rocks in either of the other domains.

Fosdick domain. The Fosdick Mountains consist of a mig-matite-gneiss complex of strikingly uniform lithologic characterfrom Birchall peaks at the west to Bird Bluff on the east. Thecomplex consists of interlayered migmatitic metasedimentaryrocks and granodiorite. These rocks provide the best oppor-tunity for direct observation of the deeper levels of continentalcrust in this segment of Marie Byrd Land. A small area ofheterogeneous high-grade paragneiss and lesser orthogneissat Scott Nunataks and Mount Swadener in the Edward VIIPeninsula are the only comparable rocks in the Ford Ranges(Adams et al. 1988).

In rare places, the protolith of the Fosdick Mountains me-tasedimentary material can be seen to be dark gray feldspathicsandstone and argillite, similar to pendants of Swanson For-mation we observed in Chester Mountains granodiorite. Themineral assemblage includes biotite, sillimanite, garnet, cor-dierite, quartz, and K-feldspar throughout the range. Grano-diorite bodies are generally thick concordant layers. Themetasedimentary migmatite has a layered internal structure,with dark and light layers of paleosome and neosome. Partialmelting was apparently quite advanced in the metasedimen-tary component, leading to the formation of block gneiss, inwhich lenses of paleosome 1-4 meters in diameter are engulfedin leucogranitic neosome. In the western part of the complex,bodies of block gneiss have been mobilized and crosscut theregional foliation. Distinctive subunits based on variations inprotolith character were not found.

Migmatization in the Fosdick Range was accompanied bythe intrusion of mafic dikes. The youngest dikes are vertical,strike northerly in general, and consist of hornblende and calcicplagioclase. Progressively older dikes are more deformed bybuckling and boudinage, rotated into parallelism with the en-closing gneiss, and metamorphosed to fine-grained biotite-feldspar granofels. Many of the blocks in the block gneissesare relict mafic dikes.

The foliation in the migmatite defines a gentle, upright an-tiform, with limbs dipping approximately 200 on both flanksof the range. Foliation is defined by compositional banding inthe gneiss; no lineation has been observed. Numerous exten-sion faults cut the foliation at a low to moderate angle. Thesefaults were observed to form conjugate sets in any given out-crop, suggesting bulk flattening of the gneiss. Intrusion ofneosome along many of these fault planes suggest that theyare syn-metamorphic. Sparse intrafolial isoclinal folds werealso observed, but hinge lines could rarely be determined. Thefoliation is folded into a large-scale close, recumbent fold pair,with an east-trending hinge, along the northern side of therange between Mount Lockhart and the Ochs Glacier.

Chester domain. The Chester Mountains consist of mediumgrained biotite granodiorite. Pendants of dark gray sandstoneand argillite with sparse calcareous nodules are present. Thegranodiorite is intruded by medium to fine-grained muscovite-biotite granite, abundant pegmatite dikes, and by mafic dikesresembling those that intrude the Fosdick migmatite-gneisscomplex. At Neptune Nunataks along the south side of thecentral Fosdick Mountains and at Griffith Nunataks to the east,are outcrops of foliated granodiorite in which the foliation isconcordant to that in nearby Fosdick migmatite-gneiss expo-sures. Pegmatite dikes crosscut this foliation. These outcropsmay represent a deeper level of the Chester Mountains bath-olith. The presence of foliation in these rocks suggests increas-ing strain toward the contact with the Fosdick complex.

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Corey domain. Mount Corey and O'Connor Nunataks consistof alkali granite, associated dikes, and minor intrusive rocks.The granite is pinkish, medium grained, and equigranular.Mafic minerals are hornblende and biotite at O'Connor Nun-ataks, and biotite at Mount Corey. A few pegmatite dikes arepresent, but mafic dikes are absent, suggesting that this graniteis younger than the mafic dikes that intrude the Fosdick andChester domains. The only deformation features observed inthis domain are planar crush zones on Mount Corey and chior-itic fractures at O'Connor Nunatak.

The outcrop pattern in the Fosdick Mountain area is con-sistent with the migmatite-gneiss complex forming the coreof a large-scale dome. The deepest crustal level is exposedin the Fosdick Mountains, with the Chester and Mount Coreydomains representing successively higher levels. The anti-formal structure of the range is related to the uplift historyof the migmatite complex. Halpern (1972) reports seven ru-bidium-strontium biotite ages from the Fosdick Mountainsthat cluster from 92 to 102 million years and these ages areregarded as a reliable estimate for the uplift and cooling ofthe migmatite-gneiss complex. These cooling ages are similarto those determined from metamorphic rocks in New Zea-land that were uplifted in response to continental extensionpreceding the breakup to the southern Gondwanaland mar-gin (Tulloch and Kimbrough 1989). Our continuing researchis directed at determining the timing and causes of uplift ofthe Fosdick migmatite-gneiss complex.

This research was supported by National Science Founda-tion grant DPP 88-17615.

References

Adams, C.J. 1987. Geochronology of granite terranes in the Ford Ranges,Marie Byrd Land, West Antarctica. New Zealand Journal Geology Geo-physics, 30, 51-72.

Adams, C.J., P. Broady, S.D. Weaver, and P.J. Cleary. 1988. Geologicaland biological studies on Edward Vii Peninsula, Marie Byrd Land, WestAntarctica. (Immediate Science Report to the Ross Dependency Re-search Committee. New Zealand Antarctic Research Program FieldSeason 1987/88: Event 151.)

Bradshaw, J.D., P.B. Andrews, and B.D. Field. 1983. Swanson Formationand related rocks of Marie Byrd Land and a comparison with theRobertson Bay Group of Northern Victoria Land. In R.L. Oliver et al.(Eds.), Antarctic earth science. Canberra: Australian Academy of Science.

Cooper, R. A., C. A. Landis, W. E. Le Mauserier, and 1G. Speden. 1982.Geologic history and regional patterns in New Zealand and WestAntarctica—Their paleotectonic and paleogeographic significance.In C. Craddock (Ed.), Antarctic geoscience. Madison: University ofWisconsin Press.

Halpern, M. 1972. Rb-Sr total-rock and mineral ages from the Mar-guerite Bay area Kohler Range and Fosdick Mountains. In R.J. Adie(Ed.), Antarctic geology and geophysics. Oslo: Universitetsforlaget.

Tulloch, A.J., and D.L. Kimbrough. 1989. The Paparoa metamorphiccore complex, Westland-Nelson, New Zealand: Cretaceous exten-sion associated with fragmentation of the Pacific margin of Gond-wana. Tectonics, 8, 1,217-1,234.

Wade, F. A., C. A. Cathey, and J. B. Oldham. 1977. Reconnaissance geo-logic map of the Guest Peninsula quadrangle, Marie Byrd Land, Antarctica.USARP, Antarctic Geological Map, A-7.

Wade, F.A., C.A. Cathey, and J.B. Oldham. 1978. Reconnaissance geo-logic map of the Gutanko Nunataks quadrangle, Marie Byrd Land, Ant-arctica. USARP, Antarctic Geological, Map A-il.

Austral summer 1989-1990at the Executive Committee Range,

Marie Byrd Land, Antarctica

W.C. MCINTOSH and K.S. PANTER

Department of GeoscienceNew Mexico Institute of Mining and Technology

Socorro, New Mexico 87801

J.L. SMELLIE

British Antarctic SurveyCambridge CB3 OET, United Kingdom

J.A. GAMBLE

Department of GeologyVictoria University

Wellington, New Zealand

The West Antarctic Volcanological Exploration (WAVE) pro-gram is a multinational effort (by the United States, the United

Kingdom, and New Zealand) to study in detail the geology ofvolcanoes in Marie Byrd Land, West Antarctica. Marie ByrdLand is Antarctica's largest but least studied volcanic province(LeMasurier 1990). It includes 18 large (greater than 2,000-meter elevation) stratovolcanoes and more than 30 smallereruptive centers. All of these volcanoes show alkaline com-positions and are related to crustal extension associated withcontinental rifting. Most Marie Byrd Land volcanoes have beenstudied only on a reconnaissance level, primarily by helicopter-supported geological parties during the 1967-1968 and 1977-1978 austral summers (LeMasurier and Rex 1989; LeMasurier1990).

During the 1989-1990 austral summer, a snowmobile-equipped, six-person WAVE team performed 23 days of fieldwork at the southern end of the Executive Committee Rangein central Marie Byrd Land. Detailed geologic mapping andsampling was completed on three volcanoes: Mount Waesche,Mount Sidley, and Mount Cummings. This article reports someof our initial field observations.

Mount Waesche. Mount Waesche (3,292 meters) is the south-ernmost and youngest of the Executive Committee Range vol-canoes (figure). It is a coalesced doublet consisting of thetopographically subdued 1.5 million year old, 10-kilometer-wide Chang Peak caldera with the younger (0.1 to 1 millionyear old), higher symmetrical southern peak of Mount Waescheproper developed on its southern flank (LeMasurier 1990). Wesampled the only three exposures on Chang Peak caldera and

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