Geological investigations in eastern Marie Byrd Land ...
Geological investigations in eastern Marie Byrd Land, West Antarctica Vic DIVENERE, Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964 J.D. BRADsHAw and S.D. WEAVER, Geology Department, University of Canterbury, Christchurch 1, New Zealand D.G. PALAIS, Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109 R.J. PANKHURST and B.C. STOREY, British Antarctic Survey, High Cross, Cambridge CB3 OET, United Kingdom
n international team, with members from the United tates, United Kingdom, and New Zealand, conducted geological investigations in the region of the Kohler Range in eastern Marie Byrd Land during the 1992-1993 austral summer. This was the final of three field seasons for the South Pacific Rim International Tectonic Expedition (SPRITE). During the 1990-1991 season, outcrops had been visited via Skidoo and Twin Otter parties in the Saunders! Ruppert/Hobbs coast area of western Marie Byrd Land. During the 1991-1992 season, outcrops in the Pine Island Bay area were visited by helicopter from the U.S. Coast Guard vessel Polar Sea. The purpose of these investigations is to develop an understanding of the evolution of the Pacific margin of the Gondwana supercontinent, particularly the relationship of Marie Byrd Land, with the remainder of West Antarctica, New Zealand, and the east antarctic craton, through field and laboratory studies of the pre-Cenozoic rocks of Marie Byrd Land. During the 1992-1993 season, a base camp was established at 75 0 10.5'S 113 024'W on the southern side of the Kohler Range (figure 1). The New Zealand Antarctic Program (NZAP) provided ground support including mountaineers, Ski-doos, camping gear, food, and clothing. The British Antarctic Survey (BAS) provided a Twin Otter aircraft and air crew. The U.S. Antarctic Program (USAP) provided LC-130 support for field put-in and take-out as well as fuel for the Twin Otter. Six geologists, two mountaineers, and a two-person air crew lived in polar tents from 27 November through 30 December 1992. The Twin Otter and air crew returned to the BAS base at Rothera on 22 December. A total of 33 days was spent in the field: 1 establishing camp, 17 doing geological work, 11 lying up in bad weather, and 4 waiting for pull-out. Outcrops were visited and sampling was conducted at 31 locations in the Kohler Range, Bear Peninsula, and Mount Murphy in eastern Marie Byrd Land (figure 1). In addition, two locations were visited on the Usas Escarpment in central Marie Byrd Land. All work was accomplished between 1 December and 24 December 1992. Travel was mostly by Twin Otter. Two teams were put in the field when weather permitted. This enabled as many as three or four locations to be visited in a single day, under ideal conditions. Sampling was conducted for paleomagnetic, geo chronological (rubidiumstrontium, zircon uranium-lead, fission track), and geochemical (x-ray florescence, XRF) laboratory analyses. The geology of eastern Marie Byrd Land has been briefly described by Wade and Wilbanks (1972) and Lopatin and Orlenko (1972) as a result of a reconnaissance survey during the 1967-1968 field season. Plutonic igneous rocks are the
dominant rock type, the most abundant being a granite-granodiorite suite with potassium-argon (K-Ar) (Wade 1972; Lopatin, Krylov, and Liapyshev 1974) and rubidium-stron tium (Rb-Sr) (Halpern 1972) ages indicating a possible Permian emplacement. Cretaceous alkali plutonic rocks are not seen in eastern Marie Byrd Land in the abundance in which they are found in western and central Marie Byrd Land, but there are a few K-Ar ages from granitic rocks (Wade 1972; Lopatin et al. 1974) indicating a Cretaceous event. Gneissic rocks on the eastern Bear Peninsula are granitoids, strongly deformed in discrete north-south trending shear zones, with development of mylonites. In contrast, basement rocks discovered at the base of Mount Murphy consti tute a paragneiss sequence, partly migmatized but with shear-
114W
112W
Figure 1. Map of study area in eastern Marie Byrd Land. Large dots are approximate locations of sampling sites. Triangle marks base camp.
ANTARCTIC JOURNAL - REVIEW 1993 5
bounded pods of marble and calc-silicate. Moderately preserved plant stems were found in fresh scree at the base of the cliff face at Rogers Spur (Bear Peninsula) where andesitic and rhyolitic volcanic agglomerate are also found Outcrops of rhyolitic lavas and ignimbrites were visited at Benes Peak and Mount Galla on the Usas Escarpment. Cenozoic volcanic rocks cap older rocks in the Kohler Range and at Mount Murphy. Preliminary paleomagnetic results from Early Bluff (101±4 million years, K-Ar; Wade 1972) and Barter Bluff are in good agreement with the approximately 100-million-year paleomagnetic results from the Ruppert/Hobbs Coast of west-central Marie Byrd Land (DiVenere, Kent, and Daiziel in preparation; DiVenere 1993). The Marie Byrd Land results are in good agreement with a 110-million-year paleomagnetic result from Thurston Island (Grunow, Kent, and Dalziel 1991); this agreement supports the conclusion that Marie Byrd Land and Thurston Island have not experienced any significant differential motion since about 100 million years ago. Comparison of the 100- to 110-million-year paleomagnetic poles for Marie Byrd Land (MBL 100) and Thurston Island (TI 110) with a synthetic apparent polar wander path for the east antarctic craton (figure 2) indicates, however, that there has been significant motion of West Antarctica (at least Marie Byrd Land and Thurston Island) with respect to East Antarctica since about 100 million years ago. The sense and amount of the off set are consistent with geological evidence for extension between East and West Antarctica (Behrendt and Cooper
Figure 2. Mid-Cretaceous paleomagnetic poles from Marie Byrd Land (MBL 100) and Thurston Island (TI 110) with circles of 63 percent confidence, compared with the apparent polar wander path for the east antarctic craton with 63 percent confidence envelope. motion between East and West Antarctica. EOS, Transactions of the American Geophysical Union, 74(16), 115. [Abstract] Grunow, A.M., D.V. Kent, and I.W.D. Dalziel. 1991. New Paleomagnetic data from Thurston Island: Implications for the tectonics of West Antarctica and Weddell Sea opening. Journal of Geophysical Research, 96(B11), 17935-17954. Halpern, M. 1972. Rb-Sr total-rock and mineral ages from the Marguerite Bay area, Kohler Range and Fosdick Mountains. In R.J. Adie (Ed.), Antarctic geology and geophysics. Oslo: Universitetsforlaget. Lopatin, B.G., A.Y. Krylov, and O.A. Liapyshev. 1974. Main tectonomagmatic stages of development of Marie Byrd Land and Eights Coast, West Antarctica according to radioactive data, Antarktika, 13,36-51. Lopatin, B.G., and E.M. Orlenko. 1972. Outline of the geology of Marie Byrd Land and the Eights Coast. In R.J. Adie (Ed.), Antarctic geology and geophysics. Oslo: Universitetsforlaget. Wade, F.A. 1972. Geologic survey of Marie Byrd Land. Antarctic Journalof the U.S., 7(5), 144-145. Wade, F.A., and J.R. Wilbanks. 1972. Geology of Marie Byrd and Ellsworth Lands. In R.J. Adie (Ed.), Antarctic geology and geophysics. Oslo: Universitetsforlaget.
1991).
We would like to thank the mountaineers (Andy Harris and John Roberts) and the air crew (pilot Lee Proudfoot and mechanic Steve Tucker) for their expert and enthusiastic support. This research was supported by National Science Foundation grants OPP 89-16470 and OPP 90-14854.
References Behrendt, J.C., and A. Cooper. 1991. Evidence of rapid Cenozoic uplift of the shoulder escarpment of the Cenozoic west antarctic rift system and a speculation on possible climate forcing. Geology, 19(4), 315-319. DiVenere, V.1., D.V. Kent, and I.W.D. Daiziel. In preparation. Mid-Cretaceous paleomagnetic results from Marie Byrd Land, West Antarctica: A test of post-100 Ma relative motion between East and West Antarctica. Journal
of Geophysical Research.
DiVenere, V.J. 1993. Mid Cretaceous paleomagnetic results from eastern Marie Byrd Land, West Antarctica: Implications for relative
ANTARCTIC JOURNAL - REVIEW 1993 6
n international team, with members from the United tates, United Kingdom, and New Zealand, conducted geological investigations in the region of the Kohler Range in eastern Marie Byrd Land during the 1992-1993 austral summer. This was the final of three field seasons for the South Pacific Rim International Tectonic Expedition (SPRITE). During the 1990-1991 season, outcrops had been visited via Skidoo and Twin Otter parties in the Saunders! Ruppert/Hobbs coast area of western Marie Byrd Land. During the 1991-1992 season, outcrops in the Pine Island Bay area were visited by helicopter from the U.S. Coast Guard vessel Polar Sea. The purpose of these investigations is to develop an understanding of the evolution of the Pacific margin of the Gondwana supercontinent, particularly the relationship of Marie Byrd Land, with the remainder of West Antarctica, New Zealand, and the east antarctic craton, through field and laboratory studies of the pre-Cenozoic rocks of Marie Byrd Land. During the 1992-1993 season, a base camp was established at 75 0 10.5'S 113 024'W on the southern side of the Kohler Range (figure 1). The New Zealand Antarctic Program (NZAP) provided ground support including mountaineers, Ski-doos, camping gear, food, and clothing. The British Antarctic Survey (BAS) provided a Twin Otter aircraft and air crew. The U.S. Antarctic Program (USAP) provided LC-130 support for field put-in and take-out as well as fuel for the Twin Otter. Six geologists, two mountaineers, and a two-person air crew lived in polar tents from 27 November through 30 December 1992. The Twin Otter and air crew returned to the BAS base at Rothera on 22 December. A total of 33 days was spent in the field: 1 establishing camp, 17 doing geological work, 11 lying up in bad weather, and 4 waiting for pull-out. Outcrops were visited and sampling was conducted at 31 locations in the Kohler Range, Bear Peninsula, and Mount Murphy in eastern Marie Byrd Land (figure 1). In addition, two locations were visited on the Usas Escarpment in central Marie Byrd Land. All work was accomplished between 1 December and 24 December 1992. Travel was mostly by Twin Otter. Two teams were put in the field when weather permitted. This enabled as many as three or four locations to be visited in a single day, under ideal conditions. Sampling was conducted for paleomagnetic, geo chronological (rubidiumstrontium, zircon uranium-lead, fission track), and geochemical (x-ray florescence, XRF) laboratory analyses. The geology of eastern Marie Byrd Land has been briefly described by Wade and Wilbanks (1972) and Lopatin and Orlenko (1972) as a result of a reconnaissance survey during the 1967-1968 field season. Plutonic igneous rocks are the
dominant rock type, the most abundant being a granite-granodiorite suite with potassium-argon (K-Ar) (Wade 1972; Lopatin, Krylov, and Liapyshev 1974) and rubidium-stron tium (Rb-Sr) (Halpern 1972) ages indicating a possible Permian emplacement. Cretaceous alkali plutonic rocks are not seen in eastern Marie Byrd Land in the abundance in which they are found in western and central Marie Byrd Land, but there are a few K-Ar ages from granitic rocks (Wade 1972; Lopatin et al. 1974) indicating a Cretaceous event. Gneissic rocks on the eastern Bear Peninsula are granitoids, strongly deformed in discrete north-south trending shear zones, with development of mylonites. In contrast, basement rocks discovered at the base of Mount Murphy consti tute a paragneiss sequence, partly migmatized but with shear-
114W
112W
Figure 1. Map of study area in eastern Marie Byrd Land. Large dots are approximate locations of sampling sites. Triangle marks base camp.
ANTARCTIC JOURNAL - REVIEW 1993 5
bounded pods of marble and calc-silicate. Moderately preserved plant stems were found in fresh scree at the base of the cliff face at Rogers Spur (Bear Peninsula) where andesitic and rhyolitic volcanic agglomerate are also found Outcrops of rhyolitic lavas and ignimbrites were visited at Benes Peak and Mount Galla on the Usas Escarpment. Cenozoic volcanic rocks cap older rocks in the Kohler Range and at Mount Murphy. Preliminary paleomagnetic results from Early Bluff (101±4 million years, K-Ar; Wade 1972) and Barter Bluff are in good agreement with the approximately 100-million-year paleomagnetic results from the Ruppert/Hobbs Coast of west-central Marie Byrd Land (DiVenere, Kent, and Daiziel in preparation; DiVenere 1993). The Marie Byrd Land results are in good agreement with a 110-million-year paleomagnetic result from Thurston Island (Grunow, Kent, and Dalziel 1991); this agreement supports the conclusion that Marie Byrd Land and Thurston Island have not experienced any significant differential motion since about 100 million years ago. Comparison of the 100- to 110-million-year paleomagnetic poles for Marie Byrd Land (MBL 100) and Thurston Island (TI 110) with a synthetic apparent polar wander path for the east antarctic craton (figure 2) indicates, however, that there has been significant motion of West Antarctica (at least Marie Byrd Land and Thurston Island) with respect to East Antarctica since about 100 million years ago. The sense and amount of the off set are consistent with geological evidence for extension between East and West Antarctica (Behrendt and Cooper
Figure 2. Mid-Cretaceous paleomagnetic poles from Marie Byrd Land (MBL 100) and Thurston Island (TI 110) with circles of 63 percent confidence, compared with the apparent polar wander path for the east antarctic craton with 63 percent confidence envelope. motion between East and West Antarctica. EOS, Transactions of the American Geophysical Union, 74(16), 115. [Abstract] Grunow, A.M., D.V. Kent, and I.W.D. Dalziel. 1991. New Paleomagnetic data from Thurston Island: Implications for the tectonics of West Antarctica and Weddell Sea opening. Journal of Geophysical Research, 96(B11), 17935-17954. Halpern, M. 1972. Rb-Sr total-rock and mineral ages from the Marguerite Bay area, Kohler Range and Fosdick Mountains. In R.J. Adie (Ed.), Antarctic geology and geophysics. Oslo: Universitetsforlaget. Lopatin, B.G., A.Y. Krylov, and O.A. Liapyshev. 1974. Main tectonomagmatic stages of development of Marie Byrd Land and Eights Coast, West Antarctica according to radioactive data, Antarktika, 13,36-51. Lopatin, B.G., and E.M. Orlenko. 1972. Outline of the geology of Marie Byrd Land and the Eights Coast. In R.J. Adie (Ed.), Antarctic geology and geophysics. Oslo: Universitetsforlaget. Wade, F.A. 1972. Geologic survey of Marie Byrd Land. Antarctic Journalof the U.S., 7(5), 144-145. Wade, F.A., and J.R. Wilbanks. 1972. Geology of Marie Byrd and Ellsworth Lands. In R.J. Adie (Ed.), Antarctic geology and geophysics. Oslo: Universitetsforlaget.
1991).
We would like to thank the mountaineers (Andy Harris and John Roberts) and the air crew (pilot Lee Proudfoot and mechanic Steve Tucker) for their expert and enthusiastic support. This research was supported by National Science Foundation grants OPP 89-16470 and OPP 90-14854.
References Behrendt, J.C., and A. Cooper. 1991. Evidence of rapid Cenozoic uplift of the shoulder escarpment of the Cenozoic west antarctic rift system and a speculation on possible climate forcing. Geology, 19(4), 315-319. DiVenere, V.1., D.V. Kent, and I.W.D. Daiziel. In preparation. Mid-Cretaceous paleomagnetic results from Marie Byrd Land, West Antarctica: A test of post-100 Ma relative motion between East and West Antarctica. Journal
of Geophysical Research.
DiVenere, V.J. 1993. Mid Cretaceous paleomagnetic results from eastern Marie Byrd Land, West Antarctica: Implications for relative
ANTARCTIC JOURNAL - REVIEW 1993 6
