Qm

Lt

Figure 3. Triangular diagram showing petrographic composition ofPagoda Formation sandstones ("ss," N = 54) and diamictites("dmct," N 21). ("Om" denotes monocrystalline quartz?' "F" de-notes "feldspar?' "Lt" denotes "lithic fragments," including poly-crystalline quartz.)

In summary, the terrestrial glacial facies assemblage, paleo-ice flow directions, and provenance data for the Pagoda Forma-tion indicate deposition in a stable cratonic region distant fromthe paleo-Pacific margin of East Antarctica. There is no evidencefor an active continental margin in the vicinity of the presentcentral Transantarctic Mountains during Permo-Carboniferoustime. These data, therefore, lend support to reconstructions ofthe Pacific margin of Gondwana which place microcontinentalblocks, now in West Antarctica and New Zealand, adjacent tothe present continental outline of East Antarctica (Daiziel andElliot 1982).

This study is based on data collected from 17 Pagoda sectionsin the Beardmore Glacier area visited during November and

December 1985. The research was supported by National Sci-ence Foundation grant DPP 84-18445.

References

Askin, R.A. 1987. Personal communication.Barrett, P.J., G.W. Grindley, and P.N. Webb. 1972. The Beacon Super-

group of East Antarctica. In R.J. Adie (Ed.), Antarctic geology andgeophysics. Oslo: Universitetsforlaget.

Berner, R.A. 1986. Personal communication.Coates, D.A. 1985. Late Paleozoic glacial patterns in the Central Trans-

antarctic Mountains, Antarctica. Antarctic Research Series, 36(13),325-338.

Collinson, J.C. In Preparation. The paleo-Pacific margin as seen fromEast Antarctica. Fifth International Symposium on Antarctic EarthSciences.

Dalziel,I.W.D., and D.H. Elliot. 1982. West Antarctica: Problem child ofGondwanaland. Tectonics, 1, 3-19.

Dickinson, W.R., L.S. Beard, G.R. Brakenridge, J.L. Erjavec, R.C. Fer-guson, K.F. Inman, R.A. Krepp, EA. Lindberg, and P.T. Ryberg.1983. Provenance of North American Phanerozoic sandstones inrelation to tectonic setting. Geological Society of America Bulletin, 94,222-235.

Elliot, D.H. 1975. Gondwana basins in Antarctica. In K.S.W. Campbell(Ed.), Gondwana geology, Canberra, Australia: National UniversityPress.

Frakes, L.A., J.L. Matthews, and J.C. Crowell. 1971. Late Paleozoicglaciation: Part Ill, Antarctica. Geological Society of America Bulletin, 82,1581-1584.

Lindsay, J.F. 1968. Stratgraphy and sedimentation of the lower Beacon rocks ofthe Queen Alexandra, Queen Elizabeth, and Holland Ranges, Antarctica,with emphasis on Paleozoic glaciation. (Ph.D. Dissertation, Ohio StateUniversity.)

Lindsay, J.F. 1970. Depositional environment of Paleozoic glacial rocksin the Central Transantarctic Mountains. Geological Society of AmericaBulletin, 83, 1149-1172.

Miller, J.M.G. In preparation. Glacial advance and retreat sequences in aPermo-Carboniferous section, central Transantarctic Mountains.

Miller, 1MG., and B.J. Waugh. 1986. Sedimentology of the PagodaFormation (Permian), Beardmore Glacier area. Antarctic Journal of theU.S., 21(5), 45-46.

S.G. BORG, J.W. GOODGE, V.C. BENNETT, and D.J. DEPAOLO

Geochemistry of granites andmetamorphic rocks: Central

Transantarctic Mountains

Department of Earth and Space SciencesUniversity of California

Los Angeles, California 90024

B.K. SMITH

Department of GeologyArizona State University

Tempe, Arizona 85287

This note summarizes our work on the late Precambrian toearly Paleozoic basement of the central Transantarctic Moun-tains from 1 June 1986 through 1 June 1987 and is intended tosupplement two reports published in the 1986 review issue ofthe Antarctic Journal (Borg et al. 1986; Borg and DePaolo 1986).Current results of specific aspects of this work are available inthree abstracts (Borg and DePaolo 1987a, 1987b; and Goodgeand Borg 1987).

Field program. Geologic mapping and sampling of granitic andmetamorphic rocks was done in the Gabbro Hills in November1986. Early Paleozoic plutonic rocks occupy a large proportionof the region (approximately 80-90 percent) and are mainlydiorite, tonalite, and granodiorite with only one gabbroic plu-ton (compare with McGregor 1965). December was spent com-pleting our mapping and sampling of the Miller Range whichwas begun in 1985-1986. Work on the structural geology of theMiller Formation and the Nimrod Group has confirmed andelaborated on our findings described last year (Borg et al. 1986).

1987 REVIEW 21

,Ross IceShelf

, ennox-King Glacier

/ 7O°E

EastAntarctic

Ice Sheet ( 5

o255075100I.I

kilometers

Axel!iIHeiberg

Glacier+

Laboratory program. The laboratory program is directed to-ward using the isotopic and chemical compositions of graniticand metamorphic rocks to elucidate the tectonomagmatic evo-lution of the east antarctic craton (EAc) margin in Early Paleozoictime. This work has already yielded results that substantiallymodify previous models. Figure 1 is a neodymium evolutiondiagram showing 143neodymium/'neodumium in epsilon no-tation (€Nd) for granitic and metamorphic rocks calculated at thetime of granite emplacement, approximately 500 million yearsago. These data demonstrate that the Miller Formation is com-posed of Archean material. This was not clear from previousgeochronological studies. Our data, when combined withstructural relations, suggest that an Archean portion of the EAC

is nearby under the polar ice sheet and strongly suggest that thebulk of the EAC may be of Archean age. The late Precambriangeoclinal turbidites (Goldie Formation) have isotopic composi-tions that require a sedimentary source other than the exposedpreexisting basement rocks. This observation is important forreconstructions of the Paleozoic tectonics. Proterozoic base-ment (approximately 1.8-2.0 billion years old) is inferred to bepresent in the Miller Range on the basis of the isotopic composi-tions of the peraluminous granites. Metaluminous granites east

10

0

0

ENd() Archean crust

D Met-Al GHIo Per-AlGHI• Goldie Fm• Miller Fm

-30 ..0.0 1.0 2.0 3.0

Age (G a)

Figure 1. Neodymium evolution diagram for granites of the centralTransantarctic Mountains and related metamorphic rocks. ("Met-AlGHI" denotes "metaluminous Granite Harbor Intrusives." "Per-AlGHI" denotes "peraluminous Granite Harbor Intrusives." "Fm" de-notes "formation:' END(i)denotes 143neodymium/1 neodymium com-position in epsilon notation. "Ga" denotes "giga annum" or billionyears.)

Mesozoic Ferrar Group and Mesozoic-Permian Beacon Super Group

Cambrian Granite Harbour Intrusives

Cambrian Byrd Group

Precambrian Beardmore Group

Precambrian Nimrod Group

Argosy Formation

Miller Formation

f__I \;s 1,. \(y

Figure 2. Geologic sketch map of the central Transantarctic Mountains. Sample locations are shown by circles. Section line A-B is perpen-dicular to structural trends of the Ross Orogeny and relates to figure 3.

22 ANTARCTIC JOURNAL

of the Marsh Glacier are inferred to be products of mixingbetween a depleted-mantle component and a crustal compo-nent.

An important feature of the data is the pattern of variationover the region. Figure 2 shows the study area, locations ofanalyzed samples, and a cross-section line perpendicular tostructural trends of the Ross Orogeny. Figure 3 shows ENd ofseveral rock types (calculated for crystallization ages of 500million years) projected onto the section line. Three crustalelements or "terranes" are indicated. The oldest is the MillerFormation, which is composed of Archean material but is con-fined to the upper plate of a major east-directed thrust zone inthe Miller Range. This material was not involved in formation ofthe granites. A second terrane is crystalline crust of Proterozoicage located between the thrust zone and the Marsh Glacier. It isidentified by the presence of peraluminous granites (whollycrustal melts) in the Miller Range, and its neodymium modelage is fixed by the isotopic compositions of these granites (fig-ure 1). The third crustal element, defined by the metaluminousgranites in the axis and the eastern side of the TransantarcticMountains, is characterized by continuous variation of initialENd of the granites from ENd equals approximately -8 to 2across the range. These granites are mixtures of mantle-derivedmagma and a Precambrian component similar to that whichproduced the peraluminous granites of the Miller Range. It isinferred that this region is underlain by thinned Proterozoiccrust. The pattern of isotopic variation in the metaluminousgranites is compatible with westward subduction of oceaniccrust beneath the EAC at the time of granite genesis. The discon-

EP El

El

t---Marsh Glacier

100200300

kilometers B

Figure 3. Neodymium composition ( 143neodymium/ 1 neodymium inepsilon notation, N) at 500 million years ago plotted against dis-tance across the Transantarctic Mountains. ("Met-Al GHI" denotes"metaluminous Granite Harbor Intrusives." "Per-Al GHI" denotes"peraluminous Granite Harbor Intrusives." "Fm" denotes"formation.")

tinuity in the isotopic and chemical compositions of the granitesat the Marsh Glacier is interpreted as a transition betweenthinned and normal-thickness crust.

These data have important implications for the early Pal-eozoic tectonic evolution of this segment of Antarctica and arealso important in defining the age, nature, and extent of thePrecambrian basement of Antarctica. Our continuing analyticalwork is aimed at broadening the geographic coverage of theisotopic variations in the granitic rocks and better defining theisotopic signature of other metamorphic rocks of the region. Thepattern of isotopic variation we are finding in the central Trans-antarctic Mountains is an important feature of the basementwhich we believe may be traceable northward. These isotopic"markers" will be valuable in working out the structural de-velopment of the Transantarctic Mountains.

We would like to thank VXE-6, National Science Foundation,Polar Operations and Antarctic Services, Inc., for their efforts insupport of our field work. This research was supported byNational Science Foundation grant DPP 83-16807.

References

Borg, S.C., and D.J. DePaolo. 1986. Geochemical investigations of lowerPaleozoic granites of the Transantarctic Mountains. Antarctic Journal ofthe U.S., 21(5), 41-43.

Borg, S.C., and D.J. DePaolo. 1987a. Isotopic studies of granites in thecentral Transantarctic Mountains (Abstract). LOS, 68,442.

Borg, S.C., and D.J. DePaolo. 1987b. Isotopic studies of lower Paleozoicgranites of the central Transantarctic Mountains (Abstract). Fifth Ant-arctic Earth Sciences Symposium, Cambridge, U.K., August, 1987.

Borg, S.C., J.W.Goodge, D.J. DePaolo, and J.M. Mattinson. 1986. Fieldstudies of granites and metamorphic rocks: Central TransantarcticMountains. Antarctic Journal of the U.S., 21(5), 43-45.

Coodge, J.W,, and S.C. Borg. 1987. Metamorphism and crustal struc-ture in the Miller Range, central Transantarctic Mountains (Abstract).Fifth Antarctic Earth Sciences Symposium, Cambridge, U.K., Au-gust, 1987.

McGregor, V. 1965. Geology of the area between the Axel Heiberg andShackleton Glaciers, Queen Maud Range, Antarctica: Part 1—Base-ment complex, structure, and glacial geology. New Zealand Journal ofGeology and Geophysics, 8,314-343.

Borg, S.C., J.W.Goodge, D.J. DePaolo, and J.M. Mattinson. 1986. Fieldstudies of granites and metamorphic rocks: Central TransantarcticMountains. Antarctic Journal of the U.S., 21(5), 43-45.

Goodge, J.W., and S.C. Borg. 1987. Metamorphism and crustal struc-ture in the Miller Range, central Transantarctic Mountains (Abstract).Fifth Antarctic Earth Sciences Symposium, Cambridge, U.K., Au-gust, 1987.

McGregor, V.R. 1965. Geology of the area between the Axel Heiberg andShackleton Glaciers, Queen Maud Range, Antarctica: Part 1—Base-ment complex, structure, and glacial geology. New Zealand Journal ofGeology and Geophysics, 8,314-343.

ENdW

-20

-300A

o Met-Al GHIo Per-Al GHI• Goldie Fm• Miller Fm

1987 REVIEW 23