Fission-Track Tectonic Studies of the Transantarctic Mountains

ment deformation features were formed during episodic rapid Collinson, L.A. Krissek, T. C. Homer, B. Lord, and J. Isbell, for sedimentation and slumping events. Pinchout of the Mackellar their assistance. just north of the Nimrod Glacier and southward-directed pal- This research was supported by National Science Foundation eocurrents suggest that the edge of the basin was to the north. grant DPP 84-18445. Lack of broadly correlative units and the abundance of discon- tinuous sand beds reflects deposition in a temporally and later- References ally complex mosaic of deltaic subenvironments. Gradual coar- Barrett, P.J. 1969. Stratigra pity and petrology of the mainly fluviatile Permian sening upward to sandstones of the Fairchild Formation and Triassic Beacon rocks, Beardmore Glacier area, Antarctica. (Ohio State represents basin filling and establishment of fluvial University Research Foundation, Institute of Polar Studies, Report 34.) Columbus: Ohio State University Press. environments. Barrett, P.J., and C. Faure. 1973. Strontium isotope compositions of non- Was the Mackellar Formation deposited under marine condi- marine carbonate rocks from the Beacon Supergroup of the Transan- tions as were portions of the correlative Polarstar Formation tarctic Mountains. Journal of Sedimentary Petrology, 43(2), 447-457. (Ellsworth Mountains; Collinson and Vavra 1982) and Discov- Bradshaw, MA., J. Newman, and J.C. Aitchison. 1984. Preliminary ery Ridge Formation (Ohio Range; Bradshaw, Newman, and geological results of the 1983-84 Ohio Range Expedition. New Zealand Aitchison 1984), or was it deposited under brackish to fresh- Antarctic Record, 5(3), 1-17. water conditions (Barrett and Faure 1973)? Low diversity and Collinson, J.W., and J. Isbell. 1986. Permo-Triassic sedimentology of the abundance of trace fossils and paucity of bioturbation may be Beardmore Glacier area. Antarctic Journal of the U.S., 21(5). characteristic of Paleozoic brackish and nonmarine facies; this Collinson, J.W., and C.L. Vavra. 1982. Sedimentology of the Polarstar Geological So- and the absence of the Permian Eurydesma body-fossil fauna Formation (Permian), Ellsworth Mountains, Antarctica. suggests deposition in brackish to freshwater environments. ciety of America, (Abstracts with Programs), 14(7), 466. Elliot, D.H. 1975. Gondwana basins in Antarctica. In K.S.W. Campbell, However, low faunal diversity and absence of shelled bottom (Ed.), Gondwana geology. Canberra: Australian National University fauna might also be caused by low-oxygen conditions and rapid Press. sedimentation, both of which were prevalent in the Mackellar Grindley, G.W. 1963. The geology of the Queen Alexandra Range, basin. Thus, although it appears that the starved post-glacial Beardmore Glacier, Ross Dependency, Antarctica; with notes on the Mackellar basin was filled with sediments which were derived correlation of Gondwana sequences. New Zealand Journal of Geology from the north and deposited in and adjacent to relatively and Geophysics, 6(3), 307-347. small-scale distributaries, the relationship between this basin Laird, MG., G.D. Mansergh, and J.M.A. Chappell. 1971. Geology of and the Pacific Ocean remains problematic. Planned additional the Central Nimrod Glacier area, Antarctica. New Zealand Journal of work, including study of the trace fossils, analyses of sequences Geology and Geophysics, 14(3), 427-468. of bedding types, petrographic analyses of sandstone and shal- La Prade, K.E. 1970. Permian-Triassic Beacon Group of the Shackleton Glacier area, Queen Maud Range, Transantarctic Mountains, Ant- es, and organic geochemical analyses of shales may clarify arctica. Geological Society of America Bulletin, 81(4), 1403-1410. provenance and depositional environments and allow more Lindsay, J.F. 1970. Depositional environment of Paleozoic glacial rocks accurate paleogeographic reconstructions. in the Central Transantarctic Mountains. Geological Society of America We would like to thank the other members of the nine-person Bulletin, 81(4), 1149-1171. Vanderbilt University and Ohio State University team (studying Miller, J.M.G., and B.J. Waugh. 1986. Sedimentology of the Pagoda the Permo-Triassic sequence in the Beardmore Glacier area) Formation (Permian), Beardmore Glacier area. Antarctic Journal of the including J.M.G. Miller and B.J. Waugh (Vanderbilt) and J.W. U. S., 21(5). 200-400 kilometers in width, and having elevations up to 4,500 Fission-track tectonic studies meters. The uplift and formation of the Transantarctic Moun- of the Transantarctic Mountains, tains have always been something of an enigma, but recent Beardmore Glacier area apatite fission-track analysis is providing important new in- formtion not only about their uplift history but also about the implications of that uplift history for the glacial history of Ant- arctica as a whole. P.G. FITZGERALD The main field objective of this project was to collect samples for fission-track analysis to determine the timing and rate of uplift of the Transantarctic Mountains and measure relative Antarctic Research Centre vertical displacements across faults within the range. As part of Victoria University Private Bag, Wellington, New Zealand the 1985-1986 Beardmore Glacier field camp, two general areas and were selected for study: the coastal region around the mouth of Department of Geology the Beardmore Glacier and further inland in the Miller and University of Melbourne Queen Elizabeth Ranges. Fieldwork was done on foot from two Parkville, Victoria, 3052, Australia helicopter-supported satellite camps as well as by close support on day trips out of Beardmore camp during the period from 23 November to 16 December 1985. The two-person field party The Transantarctic Mountains are a major transcontinental consisted of Paul Fitzgerald and Ken Woolfe, also of Victoria range stretching for some 4,000 kilometers, varying from University. 38 ANTARCTIC JOURNAL The study of mountain uplift using fission-track analysis subsidence. The amount of uplift across the mountain range is requires sampling at regular intervals over significant elevation differential; from the axis of maximum uplift about 30 kilo- ranges in order to gain information representing the greatest meters inland of the Victoria Land coast, the mountains dip possible time period. Sampling is limited to those rocks that gently westward under the polar ice cap. contain small amounts of uranium-bearing minerals. Our study The study was extended to the Beardmore Glacier area to see concentrated on apatite, a common accessory mineral in gra- whether the uplift history and tectonics varies from that ob- nitic rocks. The granites in the area outcrop dominantly along served in southern Victoria Land. In the lower Beardmore the Shackleton Coast but make up a large portion of the Miller Glacier area, we sampled every 100 meters over a 1,150-meter Range and also occur as isolated plutons elsewhere. vertical profile in the Mount Ida/Granite Pillars (83°36S Prior to working in the Beardmore Glacier area, a number of 170°35E) area just to the north of the Beardmore Glacier. To- field seasons were spent collecting data from Victoria Land. pographic evidence for faulting in this area includes a decrease Results from those studies determined the sampling strategy in height of the mountains of the Queen Alexandra Range in the employed and the areas visited during the 1985-1986 field sea- form of a number of large generalized terraces and the presence son. The results from southern Victoria Land (Fitzgerald and of scarps, for example the large scarp formed by the east face of Gleadow 1985) show a strong correlation between apatite age Mount Elizabeth (83°53S 168°34E). and sample elevation and indicate a two-stage uplift history for Near-horizontal dolerite sills in southern Victoria Land have the Transantarctic Mountains. A good example (see the table been used to determine the amount of displacement across and figure 1) of these results is a set of samples collected from faults in the Transantarctic Mountain Front. The dolerite sills in Mount Barne on the eastern end of the Kukri Hills (77°35S the Beardmore Glacier area do not outcrop at the coast, so we 163°33E) and from basement cored in the CIROS-2 (Cenozoic took horizontal sampling traverses to generate artifical refer- Investigations of the Ross Sea) drillhole (Barrett 1985), some 1.5 ence planes using apatite fission-track ages and hence confirm kilometers away in New Harbor, southern Victoria Land. the position of faults which had been suspected from analogy Results from southern Victoria Land indicate that uplift of the with other parts of the Transantarctic Mountains or from to- Transantarctic Mountains was initiated at about 50 million years pographical evidence. A horizontal sampling traverse was ago and since that time the mountains have undergone some 5 taken from Mount Hope (83°31S 171°16E) southwest to The kilometers of uplift at an average rate of 100 meters per million Cloudmaker (84°17S 169°29E). Samples were taken from each years (Gleadow and Fitzgerald in press). it is important to suspected fault block to determine relative displacements across realize, however, that this is an average rate and may well the faults and to locate the position of the vertical sampling conceal pulses of faster and slower uplift or even periods of profile with respect to the axis of maximum uplift. Fission-track analytical data for samples from the New Harbor region, southern Victoria Land. Samples were prepared using methods outlined in Gleadow

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