On a local scale, vitrinite reflectance decreases with increas- sistent with an intrusive event that was located along the con- ing distance from intrusive bodies (Homer and Krissek 1989). tinental margin of Antarctica during Jurassic time. This pattern is consistent with the effects on organic carbon distributions that were discussed above. References Vitrinite reflectance values also exhibit a regional pattern Blatt, H. 1985. Provenance studies and mudrocks. Journal of Sedimentary (table). The northern sections consistently have lower average Petrology, 55(1), 69-75. vitrinite reflectance values, and the vitrinite reflectance values Homer, T.C., and L.A. Krissek. 1987. Depositional environments of the increase progressively toward the central sections. The south- Permian Mackellar Formation, central Transantarctic Mountains: A syn- ern section has intermediate vitrinite reflectance values. This thesis of field data and mineralogy. (Abstract.) Abstract volume Fifth pattern is visible in the "lower," "middle," and "upper" Mac- International Symposium on Antarctic Earth Sciences, Cambridge, kellar Formation. England. Conclusions. Analysis of 105 samples from the Mackellar For- Homer, T.C., and L.A. Krissek. 1989, Paleogeographic interpretations mation yields an average organic carbon content of 0.40 per- using organic carbon and mineral abundance patterns in the Permian cent. Localized reductions in this value are due to the presence Mackellar Formation, Antarctica. Geographical Society of America, Ab- of intrusive bodies. Organic carbon contents are relatively uni- stracts with Programs, 21(4), 15. Krissek, L.A., and T.C. Homer. 1986. Sedimentology of fine-grained form within most sections, and organic carbon contents show Permian clastics, central Transantarctic Mountains. Antarctic Journal little regional variation with the exception of the southernmost of the U.S., 21(5), 30-32. section. The southern section was probably influenced by a Krissek, L.A., and T.C. Homer. 1987. Provenance evolution recorded different sediment source, which is also supported by a dif- by fine-grained Permian elastics, central Transantarctic Mountains. ference in paleocurrents between the northern and southern Antarctic Journal of the U.S. 22(5), 26-28. measured sections. Krissek, L.A., and T.C. Homer. In press. Provenance evolution recorded Vitrinite reflectance values help to identify altered samples by fine-grained Permian elastics, central Transantarctic Mountains. Sym- within the Mackellar Formation, and also establish regional posium volume, Fifth International Symposium on Antarctic Earth heating patterns in the Beardmore Glacier area. Within the Sciences, Cambridge, England. Mackellar Formation, the northern section has the lowest vi- Krissek, L.A., and T.C. Homer. 1988. Geochemical record of prove- nance in fine-grained Permian elastics, central Transantarctic Moun- trinite reflectance values. The average vitrinite reflectance is tains. Antarctic Journal of the U.S., 23(5), 19-21. highest in the center of the study area and decreases slightly Miller, M.F., R.S. Frisch, J.W. Collinson, and W.G. Dow. 1987. Per- in the southernmost section. This pattern of heating may have mian black shales of the central Transantarctic Mountains. Proceed- implications that extend beyond the Mackellar Formation. The ings 1987 Eastern Oil Shale Symposium. Kentucky Energy Cabinet pattern described in the Mackellar Formation would be con- Laboratory, Lexington, Kentucky. Studies of granites Details of analytical results are given in recent abstracts (Borg, DePaolo, and Smith 1989; Borg and DePaolo 1989) and in a and metamorphic rocks, manuscript submitted to the Journal of Geophysical Research (Borg, Byrd Glacier area DePaolo, and Smith in preparation). Geologic mapping and sampling of granitic and metamor- phic rocks were carried out along the north side of the Byrd S.G. BORG, D.J. DEPAOLO, and E.D. WENDLANDT Glacier, along the lower Darwin Glacier, and in the Brown Hills during January 1989. This was accomplished with a com- bination of helicopter support and ground traverses. In early Berkeley Center for Isotope Geochemistry Department of Geology and Geophysics January, a tent camp and fuel bladder (for helicopter opera- University of California tions) were placed by an LC-130 about 4 kilometers west of Berkeley, California 94720 Roadend Nunatak on Darwin Glacier near the Darwin Glacier Camp of 1978-1979 (figure). UH-1N helicopters provided sup- T.G. DRAKE port from McMurdo, commuting about 300 kilometers each way on each day of support—an arrangement that was subject to disruption by the unpredictable weather but was necessary Department of Earth and Space Sciences University of California because the north side of the Byrd Glacier is inaccessible by Los Angeles, California 90024 ground traverse. About 1,800 kilograms of rock were collected representing 40 localities. The basement in the region is composed of granitic and This paper summarizes work on the late Precambrian to early metamorphic rocks (figure). The metamorphic rocks includc Paleozoic basement of the Transantarctic Mountains from 1 both metasedimentary and metaigneous lithologies. The me- June 1988 through 1 June 1989. It supplements previous reports tasedimentary rocks are represented by complexly folded am- in the Antarctic Journal (see Borg, DePaolo, and Smith 1988). phibolite-grade banded gneisses and schists and are best exposed 1989 REVIEW 19 Roadend Nunatak Ferrar Group and Beacon Supergroup Brown Hills North of Byrd Glacier Byrd Glacier ca. 500 million year old granites o Fault lacie Canyon Granodiorite (ca. 570 m.y. old) Homey and correlative plutons 1T.--- Bluff 1111111111Homey Formation: amphibolite- grade Pr banded gneiss and migmatitic gneiss, granite pods are present locally Undifferentiated crystalline basement (includes three units above) Dame!! Nunatak South of Byrd Glacier 3$J Byrd Group !ZN I Beardmore Group Argosy Formation (Nimrod Group) Craton margin c7 projected from the Marsh Glacier East 0 50 100 Antarctic I I I kilometers Ice Sheet Geologic sketch map of the Byrd Glacier region. Compiled from Grindley and Laird (1969), Felder (1980), and our mapping. A star marks the location of our camp. at Homey Bluff along Byrd Glacier. This unit is very distinctive, but most contacts are migmatitic. A deep level of emplacement and we propose the term "Homey Formation" to describe it. is inferred for these "older" granites. Granites emplaced about The metaigneous rocks are represented by deformed and me- 500 million years ago, during the Ross Orogeny, are unequi- tamorphosed granites which have intruded the Homey For- vocally exposed only at Roadend Nunatak and in regions north mation and were themselves intruded by younger granites of the Brown Hills along the Ross Ice Shelf. These are identified about 500 million years ago. The metagranites are exemplified in the field by their lack of deformational fabrics (cf., Felder by the Carlyon Granodiorite in the Brown Hills [568 ± 10 1980). million years old as dated by Felder (1980)] but they are ex- In overall character, the metamorphic rocks of the Byrd Gla- tensively exposed in the cliffs on the north side of the upper cier area, especially the Homey Formation, resemble the Miller Byrd Glacier in the vicinity of Darnell Nunatak. The Canyon Formation in the Miller Range to the south. The Miller For- Granodiorite contains a large amount of included metamorphic mation is constrained to be greater than about 1.7 billion years material ranging from pendants several hundred meters across old and has samarium/neodymium model ages of about 2.8 in outcrop to xenoliths (and presumably xenocrysts) less than billion years (Borg, DePaolo, and Smith in preparation). It is 1 centimeter across. The contact of the metagranite with Hor- part of the East Antarctic Craton. Isotopic data on granites ney Formation is complex and has been obscured somewhat from the Miller Range and areas to the east suggest that the by deformation. Clearly discordant contacts are present in places edge of the Miller Range-type crust is at the Marsh Glacier, 20 ANTARCTIC JOURNAL immediately east of the Miller Range, and that this type of References crust does not extend beneath the region characterized by the Shackleton Limestone. If correlation of the Homey Formation Borg, S.G., and D.J. DePaolo. 1989. Crustal structure and tectonics of with the Miller Formation is corroborated, and if the edge of the Antarctic margin of Gondwana and implications for the tectonic the East Antarctic Craton (as represented by Miller Range-type development of southeastern Australia. 28th International Geolog- crust) is projected northward parallel to the average structural ical Congress, Washington, D.C., (abstract) Vol. 1, 173-174 grain in the Transantarctic Mountains, then a strike-slip fault Borg, S.G., D.J. DePaolo, and B.M. Smith. 1988. Geochemistry of can be postulated beneath the Byrd Glacier with a minimum Paleozoic granites of the Transantarctic Mountains. Antarctic Journal of the U.S., of about 125 kilometers of right-lateral offset (figure). The con- 23(5), 25-29. cept of a strike-slip fault in the Byrd Glacier had been proposed Borg, S.G., D.J. DePaolo, and B.M. Smith. 1989. Isotopic structure and tectonics of the central Transantarctic Mountains basement:Ev- by Grindley and Laird (1969) to explain the lack of continuity idence from granitoids. American Geophysical Union, Fall Meeting between the basement rocks on each side on the glacier. The 1988. EQS, 70(32), 769. idea was discussed further by Grindley (1981) in relation to Borg, 5G., D.J. DePaolo, and B.M. Smith. In preparation. Isotopic geophysical studies by Davey (1981) which suggested that a structure and tectonics of the central Transantarctic Mountains. Jour- series of rifting centers and transform faults was responsible nal of Geophysical Research. for opening of the Ross Sea. Comparison of the neodymium- Davey, F.J. 1981. Geophysical studies in the Ross Sea region. isotopic compositions of the Homey Formation and associated Journal of the Royal Society of New Zealand, 11(4), 465-479. granites with those of the Miller Formation and associated Felder, R. P. 1980.