Paper No. 13
Presentation Time: 11:30 AM
METEORITES AND ICE - A COSMIC COCKTAIL
SCHUTT, John W., Dept. of Geology - ANSMET, Case Western Reserve University, 112 A. W. Smith Bldg, Case Western Reserve University, Cleveland, OH 44106-7216, HARVEY, R.P., Dept. of Geology, Case Western Reserve University, Cleveland, OH 44106-7216 and CASSIDY, William A., Dept. of Geology and Planetary Science, University of Pittsburgh, 4107 O'Hara St, SRCC, Rm 200, Pittsbutgh, PA 15260, john.schutt@case.edu
Antarctica has proven to be a vast repository of extraterrestrial material. Prior to 1969 only four meteorites had been recovered from the frozen continent. In 1969 a serendipitous discovery by Japanese glaciologists of nine meteorite specimens found in relative close proximity in the Yamato Mountains, has subsequently led to the discovery of thousands of meteorites being discovered in Antarctica. To date, nearly 60,000 meteorite specimens have been returned and made available to the scientific community by various nationally sponsored meteorite recovery programs. The Antarctic Search for Meteorites (ANSMET) program has been funded continuously by the National Science Foundation since 1976 and has returned nearly 20,000 specimens, including many rare and unique meteorite specimens, as well as martian and lunar meteorites. A significant number of these specimens have played a seminal role in our current understanding of the formation and evolution of our solar system, Earth, Moon, Mars, and asteroids.
The large numbers of meteorites from Antarctica and the concomitant numbers of unusual types is a result of a complex, poorly understood interplay of time and ice sheet dynamics. While isolated finds on ice-free mountain slopes or in the Dry Valleys have occurred, most meteorites are found residing on bare ice surfaces or in superglacial moraines. What was surprising was the large numbers of meteorites in close proximity to each other that could be found in some special situations. Called meteorite stranding sites, these areas are associated with zones of stranded or stagnant ice near the margins of the Antarctic icesheet. These bare ice areas are thought to be ancient, deep ice. Incessant, strong katabatic winds keep the bare ice areas free of snow accumulation.
Meteorites accumulate as a surficial lag concentration by direct infall on to the ice surface and/or by ablation of the ice over long periods of time in which meteorites are entrained. Add to this scenario a component of slow horizontal and vertical ice motion to replace the ice volume lost to ablation, and significant concentrations of meteorites can form over geologic time scales. More than 10,000 meteorite specimens have been found in some large bare ice glacial systems. Many of these specimens have terrestrial residence ages of upwards of a million years.
