This work was supported in part by National Science Foun- Francis, J. 1986. Growth rings in Cretaceous Tertiary wood from Ant- dation grant DPP 88-15976. arctica and their palaeoclimatic implications. Palaeontology, 29(4), 665- 684. Jefferson, T.H. 1982. Fossil forests from the Lower Cretaceous of Alex- ander Island, Antarctica. Palaeontology, 25(4), 681-708. References Spicer, R.A., and J.T. Parrish. 1990. Latest Cretaceous wood of the central North Slope, Alaska. Palaeontology, 33, 225-242. Cook, E.R., and L.A. Kairiukstis (Eds.). 1990. Methods of dendrochron- Taylor, E.L. 1989. Tree-ring structure in woody axes from the central Dordrecht: Kluwer Academic Publications. ology. Transantarctic Mountains, Antarctica. In Proceedings of the International Creber, G.T. 1990. The south polar forest ecosystem. In T.N. Taylor and Symposium on Antarctic Research. (Hangzhou, P.R. China, May 1989.) E.L. Taylor (Ed.), Antarctic paleobiology: Its role in the reconstruction of Tianjin: China Ocean Press. Gondwana. New York: Springer-Verlag. Studies of granitic 1960s (Murtaugh 1969; Faure, Murtaugh, and Montigny 1968). Our goal is to characterize the crystalline basement rocks in and metamorphic rocks, terms of their neodymium, strontium, and oxygen isotopic Horlick and Whitmore compositions and to delineate crustal provinces (see Borg and mountains area DePaolo 1990; Borg, DePaolo, and Smith 1990). The basement in the Horlick Mountains region is composed of granitic and metamorphic rocks (see Murtaugh 1969). The S.G. BORG, D.J. DEPAOLO, E.E. DALEY, metamorphic rocks include both metasedimentary and metaig- and K.W.W. SIMS neous lithologies. At Spear Nunatak in the upper Reedy Glacier area, the metasedimentary rocks are represented by complexly Berkeley Center for Isotope Geochemistry folded amphibolite-grade banded gneisses and schists. This Department of Geology and Geophysics unit is lithologically similar to the Miller Formation in the upper University of California Nimrod Glacier region. In the lower Reedy Glacier area, meta- Berkeley, California 94720 sedimentary rocks are represented by greenschist facies gray- wacke-shale sequences, probably equivalent to the LaGorce Formation. Metaigneous rocks are represented by dacitic por- This paper reports on field work on the granitic and meta- phyritic volcanic rocks, probably Wyatt Formation, exposed at morphic basement rocks of the Transantarctic Mountains dur- Metavolcanic Mountain, in the Mims Spur region, and in the ing the 1990-1991 austral summer. It supplements previous Long Hills. Granitic rocks that have intruded these metamor- reports in Antarctic Journal (see Borg and DePaolo 1990). phic rocks range from granite to granodiorite and include de- Geologic mapping and sampling of granitic and metamorphic formed and undeformed lithologies. The deformed lithologies rocks were carried out in the Horlick Mountains (including the are associated with well-developed shear zones, and there is Wisconsin Range, the Ohio Range, Long Hills, Metavolcanic no compelling field evidence to suggest that any of these gran- Mountain, and Minna Spur) and the Whitmore Mountains dur- ites are significantly older than the undeformed lithologies. All ing the 1990-1991 austral summer. This was accomplished with of the granites in the Horlick Mountains are probably associ- a combination of Twin Otter support and ground traverses. In ated with the Cambro-Ordovician Ross Orogeny. early December, a tent camp, including several fuel drums for Analytical work is underway to characterize the granites and Twin Otter operations, was placed by LC-130 about 4 kilometers metamorphic units. This will allow us to trace basement prov- north of Metavolcanic Mountain on the east side of the upper inces delineated in the Nimrod-Shackleton Glaciers region to- Reedy Glacier (figure) for later occupancy. The field party and ward the southeast in the Transantarctic Mountains. geologic field equipment were staged at the Corridor Aerogeo- We would like to thank National Science Foundation Polar physics of the Southeastern Ross Transect Zone (CASERTZ) Operations, Kenn Borek Air Ltd., VXE-6, and Antarctic Sup- camp (figure) for Twin Otter operations. An additional fuel port Associates, Inc., for their efforts in support of our field cache was established in the northwestern Horlick Mountains work. Special thanks go to Henry Perk, Jim Pearce, and Doug by the Twin Otter crew prior to beginning science support. The Gaunt of Kenn Borek Air Ltd., and to Kevin Killilea (manager Twin Otter was used in a close-support role for reconnaissance of the CASERTZ camp) and Rick Campbell (field party liaison) geologic mapping and sampling directly from the CASERTZ of Antarctic Support Associates. This research was supported camp. Although the CASERTZ camp was approximately 1 hour by National Science Foundation grant DPP 88-16925. flight time from the nearest outcrop, it provided access to a large segment of the Transantarctic Mountains, from the upper Reedy Glacier to the Whitmore Mountains. In a close-support role, the Twin Otter proved to be ideal for our purposes, pro- References viding a large operational area with the ability to land within Borg, 5G., and D.J. DePaolo. 1990. Crustal basement provinces of the walking distance of outcrops. About 1,600 kilograms of rock Transantarctic Mountains, Ross Sea sector. Antarctic Journal of the was collected representing all the basement lithologies (79 sam- U.S., 25(5), 29-31. ples from 46 localities). Borg, 5G., D.J. DePaolo, and B.M. Smith. 1990. Isotopic structure and Our work follows up on reconnaissance studies done in the tectonics of the central Transantarctic Mountains. Journal of Geophys- Horlick Mountains by J. Murtaugh and G. Faure in the late ical Research, 95(135), 6647-6667. 24 ANTARCTIC JOURNAL Faure, G., J.G. Murtaugh, and R.J.E. Montigny. 1968. The geology and Murtaugh, J.G. 1969. Geology of the Wisconsin Range Batholith, Trans- geochronology of the basement complex of the central Transantarctic antarctic Mountains. New Zealand Journal of Geology and Geophysics, Mountains. Canadian Journal of Earth Sciences, 5, 555-560. 12(2&3), 526-550. SP Antarctica Northern Victoria Land I I I I 0 kilometers 300 I I I 0 miles 200 Ross Sea CO TI Southern cMurdo V 1..#LUII IQ OU Land Station 180 + 80S Byrd Glacier IS Marie Byrd Land çjC / Ross Ice Shelf Nimrod Glacier Central Beardmore Glacier Antarctic Shackleton Glacier Ice Sheet I Transantarctic Scott Glacier IQ CASE RTZ 0 Reedy Glacier East Antarctic Mountains Ice Sheet Wisconsin Range Camp Samples are now Whitmore being processed Mtns Light gray shading shows outcrop from this region. area in the Transantarctic Mountains. + South Pole Thiel Mtns Locations in the Transantarctic Mountains. 1991 REVIEW 25.