The development of evaporite minerals during weathering of Antarctic meteorites.

摘要

The purpose of this thesis is to advance the understanding of Antarctic weathering of meteorites (especially the development of evaporite minerals) at the scale of a single specimen and the scale of the entire population and continent. In the first paper, Scanning Electron Microscopy and Energy Dispersive Spectroscopy examination of eucrite EET790004 allowed identification of weathering phases present in the meteorite, as well as some inferences about the elemental redistribution within the specimen. Even though EET79004 is not indicated in the ANSMET database as evaporite-bearing, the outer most layer (3-4 mm) of the meteorite has its properties modified by weathering. Cracks are filled with Ca-sulfates; fusion crust vesicles are filled with large euhedral tabular Ca-S phases and small microcrystalline or amorphous K-S phases. Secondary REE carrying phases were not identified. The second paper discusses weathering of meteorites at the scale of the entire Antarctic Search for Meteorites program population. This paper updates, supplements and expands on the last Antarctic meteorite weathering census by Velbel (1988. Meteoritics 23, 151-159.) by analyzing the most recent version of the online ANSMET database that includes information about 15,263 meteorites. Meteorite compositional class and petrologic type have influence on formation of evaporites, while correlation with weathering classification is not conclusive. Number of evaporite-bearing meteorites vary also with geographic location of meteorite-bearing ice fields where the meteorites were found, and the year of collection.