Field collecting for apatite fission-track analysis of uplift history of the ...

Field collecting for apatite fission-track analysis of uplift history of the Scott Glacier area, Transantarctic Mountains EDMUND STUMP and PAUL

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Department of Geology Arizona State University Tempe, Arizona 85287-1404 ALBANUS < GLAC

During the 1987-1988 field season, we undertook a sampling program in the Scott Glacier area, for an apatite fission-track study of the uplift history of the Transantarctic Mountains in that area. Two collecting strategies were followed: • regional collecting from summits with peak heights indicated on the U.S. Geological Survey 1:250,000 topographic maps, with the goal of determining the relative uplift throughout the area, and • collecting of vertical profiles at 100-meter elevation intervals on high-relief exposures, with the goal of determining the initiation time of uplift by defining the base of an uplifted apatite annealing zone, as well as gathering information on uplift rates. The data from the Scott Glacier area will be an extension of other fission-track uplift studies in southern Victoria Land (Gleadow and Fitzgerald 1987) northern Victoria Land (Fitzgerald and Gleadow 1988), and the Beardmore Glacier area (Fitzgerald 1986). Our four-man (E. Stump, P.G. Fitzgerald, M. Stump, and L. Dean) party occupied four tent camps during the 5-week season (figure); ground transport was by snowmobile and Nansen sled. We were put into the field by Hercules LC-130 aircraft at a landing site near the Ross Ice Shelf south of O'Brien Peak. Nine peaks were collected in the vicinity of camp 1, including a 400-meter profile on Mount Salisbury. From camp 2 on Dragon's Lair Névé vertical profiles were collected from Mount Griffith, Mount Pulitzer, and Heinous Peak. The sampling on Mount Griffith covered 2,300 meters of vertical relief, on Mount Pulitzer, 1,200 meters, and on Heinous Peak, 2,300 meters. An additional 12 summit samples were collected in the vicinity of camp 2. From camp 3 we collected a 1,800-meter section on Mount Borcik. From camp 4 on the east side of Scott Glacier we collected a 1,400-meter section on Mount Zanuck, as well as a summit sample from Altar Peak. In addition, we mapped a roof pendant of metamorphic rocks at Cox Peaks which had been reported by Katz and Waterhouse (1970). Lithologies are similar to those exposed throughout the headreaches of Scott Glacier (Stump, Smit, and Self 1986). These are a metavolcanic unit equivalent to the Wyatt Formation, and an immature sedimentary unit probably equivalent to the La Gorce Formation. However, in addition to the typical association of metagraywacke and phyllite in the La Gorce Formation, metasediments at Cox Peaks contain a considerable fraction of monomict conglomerate with clast lithology the same as the matrix. Wyatt and La Gorce Formations in the Cox Peaks are in fault contact, with a right-lateral strikeslip sense of movement indicated. Returned samples are being processed through crushing, heavy- liquid separation, mounting, etching, and irradiation 12

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Location map, northern and central Scott Glacier area. (km denotes kilometer.)

for determination of apatite fission-track ages by the externaldetector method in the Fission-Track Dating Laboratory at Arizona State University. As part of this project samples collected by Fitzgerald (1986) in the Beardmore Glacier area during the 1985-1986 field season are also being analyzed. Mugs Stump and Lyle Dean provided excellent mountaineering expertise, without which the collecting would not have been so completely successful. This research was supported by National Science Foundation grant DPP 86-12938.

References

Fitzgerald, P.G. 1986. Fission-track tectonic studies of the Transantarctic Mountains, Beardmore Glacier area. Antarctic Journal of the U.S., 21(5), 38-41.

Fitzgerald, P.G., and A.J.W. Gleadow. 1988. Fission track geochron-

ology, tectonics and structure of the Transantarctic Mountains in northern Victoria Land, Antarctica. Isotope Geoscience, 73, 169-198. Gleadow, A.J.W., and P.G. Fitzgerald. 1987. Uplift history and structure of the Transantarctic Mountains: New evidence from fission track dating of basement apatites in the Dry Valleys area, southern Victoria Land. Earth and Planetary Science Letters, 82, 1-14. Katz, H.R., and B.C. Waterhouse. 1970. Geological reconnaissance of the Scott Glacier area, southeastern Queen Maud Range, Antarctica. New Zealand Journal of Geology and Geophysics, 13, 1030-1037. Stump, E., J.H. Smit, and S. Self. 1986. Timing of events during the late Proterozoic Beardmore Orogeny, Antarctica: Geological evidence from the La Gorce Mountains. Geological Society of America Bulletin, 97, 953-965. ANTARCTIC JOURNAL