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Fission Track Studies in Northern Victoria Land in the 1991-1992 Field

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Fission Track Studies in Northern Victoria Land in the 1991-1992 Field References Faure,G.,M. L. Strobel, and E. H. Hagen. 1987b. Supraglacial moraines on the east antarctic ice sheet: Evidence for ice retreat? Geological Society Faure, C., M. L. Kalistrom, and T. M. Mensing. 1984. Classification and of America Abstracts with Programs. 19(7):660. age of terrestrial boulders in the Elephant and Reckling moraines. Faure,G. and D. Buchanan. 1987. Glaciology of the east antarctic ice sheet Antarctic Journal of the U.S., 19(5):28-29. at the Allen Hills: A preliminary interpretation. Antarctic Journal of the Faure, C. and K. S. Taylor. 1985. The geology and origin of the Elephant mo- U.S., 22(5):74-75. raine on the east antarctic ice sheet. Antarctic Journal of the U.S., 20(5):12-14. Taylor, K. S. and G. Faure. 1985. The lithologies and curious distributions Faure, C., M. L. Strobel, and E. H. Hagan. 1987a. Glacial geology of the of clasts in the Elephant moraine, Allan Hills, south Victoria Land, Reckling moraine on the east antarctic ice sheet. Antarctic Journal of the Antarctica. Geological Society of America Abstracts with Programs. U.S. 22,(5):61-63. 17(6):733. Ar ages in Jurassic dolerite and basalt at Litell Rocks and the Mesa Fission track studies in northern Range have been interpreted to record movement at this time Victoria Land in the (Kreuzer et al. 1981; Elliot and Foland 1986; DeLisle and Fromm 1989). Schmierer and Bummeister (1986) suggested that paleo 1991-1992 field season magnetic results from the Bowers Supergroup were most consis- tent with remnant magnetization recorded during uplift within the Cretaceous normal polarity superchron period (118 to 83 PAUL G. FITZGERALD, THOMAS F. REDFIELD, million years ago). STEPHEN J. REYNOLDS, AND EDMUND STUMP The primary objective of this field season was to sample a detailed vertical profile over the greatest elevation range possible from the higher peaks of the Admiralty Mountains. Fission track Department of Geology dating of the profile samples would help in the acquisition of Arizona State University information about thermotectonic events from the Cretaceous Tempe, Arizona 85287-1404 and early Cenozoic periods. • The linking of the area of extreme uplift in the southeastern part of NVL with the rest of NVL. The 10-kilometer total uplift postu A previous reconnaissance fission track study in northern lated for the southeastern part of NVL (the Mount Murchison and Victoria Land (Fitzgerald and Gleadow 1988) determined that lower Tucker Glacier areas) is considerably greater than total uplift and denudation responsible for the formation of the uplift estimates for the rest of NVL. Horizontal and vertical Transantarctic Mountains (TAM) began about 55 million years traverses linking the Murchison area with the Admiralty Moun- ago. The pattern of apatite ages with elevation over most of tains could help determine if the areas have the same timing of northern Victoria Land (NVL) is similar to individual vertical initiation of uplift (about 55 million years ago) and different profiles collected in southern Victoria Land (SVL) (Fitzgerald amounts of uplift and denudation, as was suggested by Fitzgerald 1992): Age profiles show a distinctive "break-in slope" about 50 and Gleadow (1988). Alternatively, uplift could have begun to 55 million years ago, with samples above the break-in slope earlier in the Mount Murchison area. defining a shallow gradient and those below the break defining The team planned to collect a suite of samples at a locality a steep gradient. Track length distributions below the break-in between the two different areas with different amounts of uplift slope have long means (greater than 14 microns) with small to resolve the questions of different amounts of uplift and/or standard deviations indicative of rapid cooling, whereas those different timing of uplift. The area selected for this was Mount above the break have shorter mean lengths (12-13 microns) with Supernal, a high granitic peak midway between the Mount larger standard deviations indicative of more complex thermal Murchison area (extreme uplift) and the rest of NVL (less ex- histories. Samples below the break were quickly cooled because treme, more regional uplift). of rapid uplift and denudation in the early Cenozoic, whereas • The pattern of post-Jurassic uplift in NVL. Fitzgerald and samples above the break in slope resided for some time in an Gleadow (1988) postulated a very simple pattern of uplift over apatite partial annealing zone, before early Cenozoic uplift. NVL, with approximately 10 kilometers in the southeastern The 1991-1992 field season in NVL was designed to further the coastal area and 5 to 6 kilometers over the rest of NVL, the am- scope of the reconnaissance study. We targeted specific areas ount decreasing inland toward the Wilkes subglacial basin. Roland where a carefully planned sampling strategy could address three and Tessensobn (1987) proposed two axes of uplift in NVL, an main tectonic problems. The areas and problems were as follows: older axis (the Rennick trend) responsible for the main phase of The question of Cretaceous uplift and denudation. Antarctica graben formation that possibly occurred during the early Creta- and Australia separated by continental extension during the ceous, and a younger axis (the Borchgrevink trend) that parallels Jurassic to the mid-Cretaceous (Veevers 1988). It would seem the coast from the Admiralty Mountains to the Deep Freeze Range; logical that some uplift of the TAM (especially in NVL, near they speculated that this trend was responsible for the formation where rifting presumably was first initiated) would accompany of the rift shoulder adjacent to the Ross Sea. The younger event continent-continent breakup. would give a northwest tilt to the entire NVL block inland of this Reconnassiance fission track data from the Admiralty Moun- axis. The two trends intersect in the Deep Freeze Mountains, which tains tentatively suggests that a Cretaceous uplift signature is has the greatest amount of terrain over 3,000meters in elevation recorded there (Fitzgerald and Stump 1991). Early Cretaceous K- (although the highest peaks are in the Admiralty Mountains). 12 ANTARCTIC JOURNAL 1660E 1680E Robertson Bay Terrane Vilson Boss —Admiralty I [Terrane Pe k Mountains Mt. 1P 72°S A \ N Mt. Supernal Figure 2. Location map, central northern Victoria Land. Camps are Mt. U marked by solid triangles and approximate skidoo traverse routes Deep by solid lines. RG Rastorfer Glacier. Boxed area marks location of Freeze figure 3. Range 1680E 168030E U 50 km 71045S Terra Nova Bay . II I i 0 Black Prince Volcanics ( Admiralty Intrusives Robertson Bay Group Figure 1. Simplified tectonic map of Victoria Land north of Terra Figure 3. Location and geological sketch map, Admiralty Mountains. Nova Bay, showing terranes, uplift trends (hollow lines, the Rennick Camps are marked by solid triangles and approximate skidoo traverse trend; dark lines, the Borchgrevink trend) of Roland and Tessensohn routes by thin solid lines. Collecting routes are indicated by thicker (71987), and localities mentioned in the text. Boxed area marks solid lines and solid dots. Geology is from Findlay and Jordan lcation of figure 2. Adapted from Roland and Tessensohn (1987) (1984), Ganovex Team (1987), and field observations. Mnd Fitzgerald and Gleadow (1988). The above two scenarios are necessarily speculative. While weather days during field operations) hampered many of our }itzgerald and Gleadow (1988) documented a major period of efforts to collect samples. After landing by LC-130 in the upper i.kplift and denudation in NVL that was initiated in the early Tucker Glacier, 2 kilometers north of Boss Peak on 18 November Cenozoic, the fission track data do not unequivocally describe the (figure 1, 2), we traversed 120 kilometers (figure 2) to a camp on regional extent of that uplift. Nor do the data define tectonic the north branch of the upper Fowlie Glacier (figure 3). Samples vents occurring before or after the initiation of uplift. Fission at approximately 100-meter vertical intervals over 891 meters of track thermochronology built upon a more complete data set relief (from the summit, 4,010 to 3,119 meters) were collected from could constrain these scenarios. Samples collected on either side the north side of Mount Adam during a ten-day period. Change- of major terrane boundary faults would also further determine the able weather, deep snow, and high winds hampered this phase of role of these faults in the post-Jurassic tectonic evolution of NVL. field work. The three questions posed above were the order of priorities Electrical failure of both Southcom SC-130 radios necessitated for our project in the 1991-1992 austral summer. Fitzgerald, a Twin Otter resupply flight on 3 December. We moved camp Redfield, Reynolds, and Charles Hobbs (mountain guide) were from the north branch of the Fowlie Glacier to the south branch the field team. Unfortunately a 10-day delay before put-in and on 7 December. We collected samples down the lower northwest atrocious weather during the season (more than 65 percent bad ridge of Mount Royalist from an elevation of 3,250 meters to 2,750 1992 REVIEW 13 meters. We extended the profile to even lower elevations by References sampling a small granitic nunatak under the northwest shoulder of Mount Black Prince and a previously unmapped granitic body Delisle, C., and K. Fromm. 1989. Further evidence for a Cretaceous therm at 71.68540 S 167.9676° E. Granite was also sighted at previously event in north Victoria Land. Geologisches Jahrbuch, E38:143-151. unmapped localities in bluffs to the west and north of this Elliot, D. H., and K. A. Foland. 1986. Potassium-argon age determination, of the Kirkpatrick Basalt, Mesa Range. In E. Stump (Ed.), Geologica nunatak. We collected 23 samples in total, over an elevation investigations in northern Victoria Land.
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