Journal Article Discovery of natural MgSiO3 tetragonal garnet in a shocked chondritic meteorite

富岡, 尚敬  ,  宮原, 正明  ,  伊藤, 元雄  ,  TOMIOKA, Naotaka  ,  MIYAHARA, Masaaki  ,  ITO, Motoo

2 ( 3 )  , p.e1501725 , 2016-03-25 , American Association for the Advancement of Science
ISSN:23752548
Description
MgSiO3 tetragonal garnet, which is the last of the missing phases of experimentally predicted high-pressure polymorphs of pyroxene, has been discovered in a shocked meteorite. The garnet is formed from low-Ca pyroxene in the host rock through a solid-state transformation at 17 to 20 GPa and 1900° to 2000°C. On the basis of the degree of cation ordering in its crystal structure, which can be deduced from electron diffraction intensities, the cooling rate of the shock-induced melt veins from ~2000°C was estimated to be higher than 103°C/s. This cooling rate sets the upper bound for the shock-temperature increase in the bulk meteorite at ~900°C.
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