Studies of Antarctic meteorites: A statistical comparison of Antarctic finds and non-Antarctic falls; and the origin and significance of cosmic dust from the Walcott Neve, Antarctica.

摘要

The masses and numbers of meteorites in four meteorite samples (the modern falls (MF), Antarctic finds (AF), Yamato finds (YAM) and Allan Hills Main icefield finds (ALH)) are compared. The mass frequency distributions and the proportions of different classes of meteorites differ between Antarctic finds and modern falls. Several well known distributions, when compared to the samples, give varying degrees of fit. When Antarctic post-fall processing is empirically corrected for, the proportions of different types converge for the AF and MF samples. There is an excess in numbers of small H chondrites in AF sample relative to the MF sample which cannot be corrected for in this manner.; In four of six sediment samples returned from locations around the Walcott Neve area of Antarctica, a high concentration of ablation spherules was found, averaging roughly 20 spherules per g bulk sediment. These concentrations have an origin similar to that of Antarctic meteorites; strong katabatic winds cause cosmic dust ablating out of blue ice to be transported downwind and downslope to the nearest aeolian sediment trap. In the Walcott Neve, these traps are the crests of moraines, weathering debris around boulders and rough, exposed areas of snow. Their content of ablation spherules is similar to Greenland and Cap Prudhomme sediments, with the exception of a slightly higher proportion of high-Mg glassy spheres, a large number of {dollar}>{dollar}500 {dollar}mu{dollar}m-sized spherules, and a few extremely large (between 1 mm and 1cm) "mini-meteorites" from a firn sample. Most of the spherules are essentially unweathered; however, a great range in weathering is also observed. Only a small number of "unmelted" micrometeorites have been found by comparison to the Greenland and Cap Prudhomme sediments. They may truly be missing, or may be camouflaged by local terrestrial debris.