The Kirkpatrick Basalt, Mesa Range, V1640E northern Victoria Land The D. H. ELLIoT, M. SIDERS, C. FAURE, and K. S. TAYLOR cop c V 0 Cl Institute of Polar Studies U and Department of Geology and Mineralogy P0Z Evans Névé Ohio State University Columbus, Ohio 43210 Solo N.% Wgote Peak Pain Mesa 1 As part of the Northern Victoria Land Project, we examined Half—RatI017 $ -730S N W6 the Kirkpatrick Basalt of northern Victoria Land between early Sheehan Mes Mills Valley November 1981 and mid-January 1982. We measured and sampled stratigraphic sections at Solo Nunatak, Pain Mesa (Mills Valley), Tobin Mesa, and Sheehan Mesa (figure). In addi- Section tion, we examined the Kirkpatrick Basalt at Agate Peak and the Tobin Mesa :. Ferrar Dolerite at Section Peak, Vantage Hills, and Exposure Hill (figure). The base of the basalt sequence is exposed only at the south- Gair ern end of Gair Mesa, where it rests on Beacon strata that were, Me3j.5holrnP 0 km 40 Hls subsequent to lava eruption, intruded by diabase sills. No lavas Vantage;Exposure Hills Ferrar Supergroup are present west of the Rennick Glacier in the Section Peak to Hills Beacon Supergroup c Vantage Hills area, contrary to earlier reports (Gair 1967). At and Ferrar Supergroup Agate Peak (Nathan and Schulte 1968) the lowest exposed lava, a Undifferentiated bedrock pillow basalt, is overlain by a thick pyroclastic bed containing El I blocks of sediment similar to the Mawson Formation that sepa- rates rocks of the Beacon Supergroup from the Kirkpatrick Location map for the Mesa Range region of northern Victoria Land. Basalt in southern Victoria Land. It is possible that the Agate Peak rocks are close to the base of the Kirkpatrick Basalt. Contin- uous stratigraphic sections in the Mesa Range are more than 670 meters thick, and the total stratigraphic thickness in the range Glacier (Sheehan Mesa to Monument Nunataks) may not be may well exceed 800 meters. As many as 40 flows are present in stratigraphically higher than the Mesa Range. several places where sections were measured. If a tentative Petrographically the lavas are typical tholeiites, having two correlation between Solo Nunatak and the Mills Valley is con- pyroxenes, plagioclase, and opaques set in a groundmass that firmed by later study, the total thickness will be more than 1,000 ranges from glassy through cryptocrystalline to micro- meters, and the number of flows more than 50. Flow thick- crystalline aggregates of quartzofeldspathic minerals, with or nesses range from less than 1 meter to possibly as much as 100 without ferromagnesian minerals (principally pyroxene). meters. Sills may be present within the lava sequence, but none Zeolites (stilbite and probably others) and other secondary min- have been positively identified. Sedimentary interbeds occur erals including quartz (chalcedony) and calcite are a common sporadically in the section, but no widespread units have been occurrence, filling vesicles in the upper parts of flows, as well as identified; all sedimentary interbeds found so far in situ consist forming masses within the rubbly flow tops and between the of reworked volcanic material. Lake beds such as occur at Car- pillows at Agate Peak and elsewhere. apace Nunatak (Ball et al. 1979) and in the Beardmore Glacier Selected samples collected this season will be analyzed geo- region (Tasch 1970) have been found only as disrupted blocks of chemically for major- and trace-element, rare-earth, and stron- conchostracan-bearing sediment caught up in the pillow basalt tium-isotopic data. The study of zeolites and other secondary at Agate Peak. Fossil wood has been found in a number of minerals will include identifying mineral and establishing a places. The presence of a 60-meter (200-foot) sedimentary inter- zonation (if possible) and the relationship to temperature dis- bed that was recorded by Gair on Silva Ridge has not been tribution and groundwater circulation in the lava pile. confirmed. Major faulting has been postulated for the Rennick Glacier Correlation of flows within the Mesa Range is possible only region (Gair 1967; Gair et al. 1969), and it has been suggested where flows have distinctive characteristics. Two that appear to that the Kirkpatrick Basalts are situated within a graben, the be very widespread have been identified; one is a thick black "Rennick Graben" (Kyle and Cole 1974). There is no compelling basalt that caps much of the Mesa Range, and the other is a evidence for a major fault at the head of the Rennick Glacier composite flow with a remarkable wavy unit at its top which between Vantage Hills and Exposure Hill. The lavas have a very occurs near the base of Tobin Mesa. Correlation from the Mesa low-angle regional dip to the west or northwest, and it is clear Range to other outcrops is more problematic, but may be aided that a fault may exist between Sheehan Mesa and Section Peak. by information about the chemical and isotopic compositions of Therefore, the postulated fault must have a scissorslike charac- the flows. Tentative identification of flows suggests that the ter, opening to the north. Sheehan Mesa section is largely encompassed by that of the This study was supported by National Science Foundation Mesa Range. If this is correct, the outcrops west of the Rennick grant DPP 80-21401. 19 1982 REVIEW References and C. Craddock (Eds.), Geologic maps of Antarctica 1:100,000, Antarctic maps folio series. New York: American Geographical Society. Ball, H. W., Borns, H. W., Hall, B. A., Brooks, H. K., Carpenter, F. M., Kyle, P. R., and Cole, J. W. 1974. Structural control of volcanism in the and Delevoryas, T. 1979. In B. Laskar and C. S. Raja Rao (Eds.), Fourth McMurdo volcanic group. Bulletin Volcanologique, 38, 16-25. International Gondwana Symposium (Vol. 1). Delhi: Hindustan Publish- ing Corporation. Nathan, S., and Schulte, F. J. 1968. Geology and petrology of the Camp- bell-Aviator Divide, northern Victoria Land, Antarctica. New Zealand Gair, H. S. 1967. The geology from the upper Rennick Glacier to the Journal of Geology and Geophysics, 11, 960-975. coast, northern Victoria Land. New Zealand Journal of Geology and Geophysics, 10, 309-344. Tasch, P. 1970. Antarctic and other Gondwana conchostracans and insects: New data; Significance for continental drift. In S. H. Haugh- Gair, H. S., Sturm, A., Carryer, S. J., and Grindley, G. W. 1969. The ton (Ed.), Second Gondwana Symposium. Pretoria, South Africa: Coun- geology of northern Victoria Land (Folio 12, Plate 12). In V. C. Bushnell cil of Scientific and Industrial Research. Paleomagnetic results from the samples from 15 sites in 15 flows) (figure 1). Paleomagnetic results show that the samples possess strong normal rema- Kirkpatrick Basalt Group, nence, with stability equal to or greater than that of Ferrar Victoria Land Supergroup dolerites and gabbros. The natural remanent mag- netization (NRM) includes a small viscous component that is readily removed by alternating field demagnetization in fields WILLIAM C. MCINTOSH of 20 to 50 millitesla. The mean VGP of the David Glacier samples lies at 55°S 138°W, which is nearly coincident with the average of VGPs previously reported from the Ferrar Supergroup. The New Mexico Bureau of Mines and Mineral Resources Socorro, New Mexico 87801 mean VGP of the Mesa Range samples, however, lies signifi- cantly farther south at 64°S 150°W (figure 2) (page 22). PHILIP R. KYLE It is unlikely that the anomalously high latitude of the mean VGP of the Mesa Range samples is an effect of unremoved Department Geoscience of viscous or chemical components, tectonic tilting or rotation, or New Mexico Institute of Mining and Technology Socorro, New Mexico 87801 incomplete averaging of paleosecular variation. In addition, an ERIC M. CHERRY and HALLAN C. NOLTIMIER 162E Department of Geology and Mineralogy Ohio State University Columbus, Ohio 43210 Li -i s etop5 Several previous paleomagnetic studies have been made of Jurassic-age antarctic igneous rocks, including (as summarized and referenced in the table): (1) Ferrar Dolerite sills from four SECTION localities along the Transantarctic Mountains; (2) Forrestal Gab- PEAK 1.2 I I bros from the Dufek Stratiform Intrusion; (3) Kirkpatrick Basalt 158E 15YE -7548S BRIMSTONE- lava flows from the Queen Alexandra Range in the central PEAK c_3"\ Transantarctic Mountains; and (4) tholeiites from Queen Maude 7 to I I to6 Land. The results have shown generally high stabilities and I predominantly normal polarities. The average virtual geomag- Gorgon Itol4 netic pole (vcP) is near 55°S 140°W, in good agreement with li -75303 Jurassic VGPs of Africa, South America, India, and Australia in GRIFFIN NUNATAK - their Gondwanaland configurations (Schmidt 1976). 10km 1 10 km The purpose of the present study was to investigate further DAVID GLACIER AREA MESA RANGE AREA the paleomagnetism of the Kirkpatrick Basalts. Oriented sam- ples were collected from Kirkpatrick Basalts in the David Glacier Figure 1. Map showing location of sample sites in the David Glacier Area, southern Victoria Land (55 samples from 25 sites in 24 area, southern Victoria Land, and at the Mesa Range, northern flows), and at the Mesa Range, northern Victoria Land (60 Victoria Land. 20 ANTARCTIC JOURNAL.