Combining Observations of Shock-induced Minerals with Calculations to Constrain the Shock History of Meteorites.

Details Combining Observations of Shock-induced Minerals with Calculations to Constrain the Shock History of Meteorites. Combining Observations of Shock-induced Minerals with Calculations to Constrain the Shock History of Meteorites.

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmmr54a..04d&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #MR54A-04

Physics

3662 Meteorite Mineralogy And Petrology (1028, 6240), 3919 Equations Of State, 3924 High-Pressure Behavior, 6022 Impact Phenomena (5420, 8136), 6240 Meteorites And Tektites (1028, 3662)

Scientific paper

All available evidence from shock Hugoniot and release adiabat measurements and from shock recovery experiments supports the hypothesis that the conditions for shock-induced phase transitions are similar to the conditions under which quasistatic phase transitions are observed. Transitions that require high temperatures under quasistatic pressures require high temperatures under shock pressures. The high-pressure phases found in shocked meteorites are almost invariably associated with shock melt veins. A shock melt vein is analogous to a pseudotachylite, a sheet of locally melted material that was quenched by conduction to surrounding cooler material. The mechanism by which shock melt veins form is not known; possible mechanisms include shock collisions, shock interactions with cracks and pores, and adiabatic shear. If one assumes that the phases within the vein crystallized in their stability fields, then available static high-pressure data constrain the shock pressure range over which the vein solidified. Since the veins have a sheet-like geometry, one may use one-dimensional heat flow calculations to constrain the cooling and crystallization history of the veins (Langenhorst and Poirier, 2000). Although the formation mechanism of a melt vein may involve transient pressure excursions, pressure equilibration of a mm-wide vein will be complete within about a microsecond, whereas thermal equilibration will require seconds. Some of our melt vein studies have indicated that the highly-shocked L chondrite meteorites were exposed to a narrow range of shock pressures, e.g., 18-25 GPa, over a minimum duration of the order of a second. We have used the Autodyn(TM) wave propagation code to calculate details of plausible impacts on the L-chondrite parent body for a variety of possible parent body stratigraphies. We infer that some meteorites probably represent material that was shocked at a depth of >10 km in their parent bodies.

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