Allan Hills Main Icefield
The Allan Hills Main Icefield was the first meteorite concentration locality or stranding site found in the Transantarctic Mountains. The Allan Hills Main Icefield is located immediately west of the Y-shaped Allan Hills nunatak (ALH-DAV- Figure 1 - 46 KB JPEG). The area is covered by the U.S.G.S. 1:250000 scale Convoy Range quadrangle. Approximately 75 square kilometers of ice is exposed on this northward trending icefield. Nearly 22 kilometers long and 7.5 kilometers at the widest point, this icefield has yielded approximately 1200 named meteorites. ALH1-Figure 1 (68 KB JPEG), an enlarged portion of a satellite image, shows the area covered by the Main Icefield map sheets and the locations of two slope profiles. The two slope profiles (ALH1-Figure 2- 12 KB JPEG) are give in order to show the general topographic trend in the area. Annexstad (1983) and Faure and Buchanan (1987) provide detailed descriptions of the Main Icefield area, and attempt to explain the meteorite concentration mechanism(s). Delisle et al. (1989 and 1991) conducted a radio-echo sounding survey across the Main Icefield in order to define ice thickness and bottom topography.
At the close of the 1976-1977 field season a helicopter reconnaissance visit resulted in the recovery of 45 specimens representing 9 individual meteorites. This was the first concentration of meteorites discovered from icefields in the Transantarctic Mountains. Detailed foot searches in the next two seasons produced nearly 560 specimens. A total of 85 specimens were recovered in random searches during visits to the Main Icefield in the 1979-1980 and 1980-1981 seasons. Systematic searching was continued during the 1981-1982 season when nearly all of the exposed ice area of the Main Icefield was searched in detail or visited on reconnaissance traverses, resulting in 261 specimens being recovered. Brief periodic return visits by ANSMET expeditions have resulted in additional finds in the 1983-1984 (28), 1984-1985 (35), 1985-1986 (17), 1986-1987(13), 1987-1988 (6), and 1990-1991 (6) seasons. During the 1988-1989 season a German expedition (GANOVEX) conducting radio-echo sounding studies in the area recovered 163 specimens from the Main Icefield (Delisle et al, 1989). These meteorites were transferred to the EUROMET group for curation. During the 1994-95 season a field party studying dust bands in the ice recovered 20 meteorite specimens from the Main Icefield. In the 1995-96 season this same field party collected another 10 small meteorites. A brief visit while conducting GPS survey of the base stations at the Main Icefield during the 1999-2000 season resulted in a single meteorite find. During the 1999-2000 and 2003-2004 field season other researchers conducting studies in the arera recovered another three specimens.
ALH1-Table 1 gives a tabulation of meteorite types from the 1979-2004 Allan Hills Main Icefield collections.
A small number of meteorites have been found in the vicinity of the Allan Hills or on the Main Icefield areas not covered by the map sections. One specimen (ALH 84243) was found on bedrock in Man Haul Bay, far removed from any ice (ALH1-Figure 1- 68 KB JPEG). Only one meteorite has been found on the ice in Man Haul Bay (see Yanai 1984). Seven meteorites (ALHA81037, ALHA81093, ALHA81100, ALH 84056, ALH 84071, ALH 84101, and ALH 85122) have been found on ice during random traverse and searches north of the main search area (ALH1-Figure 1- 68 KB JPEG). Other meteorites have been found on outcrop, apparently stranded by retreating ice. Three specimens (ALH 85037, ALH 85048, ALH 85123) were found on bedrock 2-4 meters above the present ice surface on a small nunatak near the south end of the icefield.
Most of the meteorite locations on the Main Icefield have been referenced to the survey network established by Nishio and Annexstad (1979) or to surveyed geographic features. Field note and sketch map data were used to document the locations of meteorites found during the 1979-80 and 1980-81 seasons. Crude locating or surveying methods (pelorus and snowmobile odometer) were used in the 1981-1982 season. In the 1983-1984 season we began to use a theodolite and EDM to precisely survey meteorite locations. The locations of the 1986-1987 meteorites were obtained from sketch map data provided by Gunter Faure. All meteorites that were not surveyed with the theodolite/EDM were plotted on a hand-drawn base map. The data points were then digitized along with the geographic features. The map was generated from merged databases of digitized and computed meteorite locations. Therefore, even though most of the meteorite locations not derived from the theodolite/EDM survey are not precisely determined, the locations of those meteorites found within a given season are accurately shown relative to one another. Since there are many precise control stations, the meteorite locations determined by the different location methods can be constrained so that the map accurately shows the relative distribution of meteorites on the icefield.
For additional information on the meteorites from the 1988 collection, refer to Meteoritical Bulletins 69, 70, 72, 77, and 80 (Wlotzka 1990; Wlotzka 1991; Wlotzka 1992; Wlotzka 1994; Grossman 1995).
Acknowledgments; We thank John Annexstad, William Cassidy, Fumihiko Nishio, and Louis Rancitelli (1979-1980); John Annexstad, William Cassidy, Harry McSween, Louis Rancitelli, Ludolf Schultz, and John Schutt (1980-1981); William Cassidy, Ghislaine Crozaz, Robert Fudali,and Ursula Marvin, and John Schutt (1981-1982); Robert Fudali, A.C. Hitch, Kunihiko Nishiizumi, Paul Pellas, Ludolf Schultz, John Schutt, and Paul Sipiera (1983-1984); William Cassidy, Catherine King-Frazier, Scott Sandford, Roberta Score, John Schutt, Robert Walker, and Carl Thompson (1984-1985); Ludolf Schultz, Ernst Zinner, and Michael Zolensky (1985-1986); Sue Iveson, Miriam Jackson, Suzanne Traub-Metlay, John Schutt, and Peter Wasilewski (1990-1991) for their contributions to the Allan Hills Main Icefield Meteorite Location Map. We also thank David Buchanan, Gunter Faure, Eric Hagen, and Michael Strobel for contributing to the Main Icefield meteorite collection and mapping project in the 1986-1987 season. Their efforts were supported by NSF Grant DPP 83-14136. Ludolf Schultz provided location data for meteorites recovered in the 1988-1989 season. We appreciate the continuity of effort by John Annexstad, Georg Delisle, Ludolf Schultz, and Joachim Sievers in determining the positions of the meteorites recovered by the GANOVEX expedition. Nelia Dunbar, Rich Esser, and Bill Macintosh provided the samples from the 1994-95 and 1995-96 seasons as well as the position data. John Schutt contributed the 1999 sample. A group led by Blue Spikes contributed the two specimens found during the 2003-2004 season.
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