Meteorites:
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Washington University in St. Louis |
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Microsampling Raman spectroscopy is an ideal technique for the non-destructive characterization of minerals and their polymorphs on a microscale and can be done in-situ in a geological thin-section. This makes it ideally suited for the study of problems of interest to meteoriticists. One exciting new area of research concerns the Raman spectroscopic identification of high-pressure polymorphs of olivine, pyroxene and apatite (e.g., wadsleyite , ringwoodite, majorite , phase A) in heavily shocked meteorites. An additional advantage of the Raman technique is that it allows the identification of shock-induced densified silica glasses. In collaboration with Dr. Ahmed El Goresy (Max Planck Institute for Cosmochemistry in Mainz, Germany), Dr. Ming Chen (Institute of Geochemistry of the Chinese Academy of Sciences in Guangzhou), and Dr. Tom Sharp (Arizona State University), we studied the heavily shocked L6 chondrites Mbale, Peace River, Sixiangkou, and Tenham , and the SNC meteorite Shergotty. The interpretation of the presence and/or absence of shock-induced high-pressure phases in such chondritic and differentiated meteorites in terms of possible solid-state transformations, high-pressure liquidus phases, and alkali vapor fractionation is not only of interest to the meteoriticist, but it also opens up a new window to the understanding of the mineralogy of the Earth's mantle. Our understanding and interpretation of shock-induced phase transformations and of high-pressure and -temperature conditions in shocked meteorites is unfortunately complicated by the fact that dynamic shock experiments in the laboratory do not result in the same effects due to the extremely short duration of the peak pressures in the experiments compared to that in the natural events. Mineralogy clearly is not what it used to be, and "getting out into the field" has taken on a whole new meaning for some geologists! |
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