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High-pressure mineral assemblages in shocked meteorites and shocked terrestrial rocks: Mechanisms of phase transformations and constraints to pressure and temperature histories

By
Philippe Gillet
Philippe Gillet
Laboratoire de Sciences de la Terre, Ecole Normale Supérieure de Lyon et Université Lyon I (UMR CNRS 5570), 46 Allée d'Italie, 69364 Lyon Cedex, France
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Ahmed El Goresy
Ahmed El Goresy
Bayerisches Geoinstitut, Universität Bayreuth, D-95440 Bayreuth, Germany
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Pierre Beck
Pierre Beck
Laboratoire de Sciences de la Terre, Ecole Normale Supérieure de Lyon et Université Lyon I (UMR CNRS 5570), 46 Allée d'Italie, 69364 Lyon Cedex, France
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Ming Chen
Ming Chen
Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Wushan, Guangzhou 510640, China
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Published:
January 01, 2007

After an overview of the most recent results of static high-pressure and high-temperature experiments, we present a review of the mineralogy of shocked meteorites. The high-pressure minerals in these rocks result either from solid-state reactions or from the crystallization of melts at high pressures. Comparisons of naturally shocked samples with samples processed in dynamic experiments must be made with extreme caution. The durations of the equilibrium shock pressure experienced by meteorites can vary over at least three orders of magnitude (10−2 s to 10 s), and they lie within the lower range of the duration of static experiments conducted in diamond anvil cells or multianvil apparatus. We emphasize that dynamic experiments up to 130 GPa have never produced any reconstructive solid-state phase transition or liquidus high-pressure minerals that offer a reliable calibration of the continuum of shock pressures and temperatures. The solid-state transformations observed in shocked meteorites are in many cases incomplete and provide only insights into the initial stages of high-pressure phase transitions, crystallization, and chemical interdiffusion. In contrast, the natural high-pressure species crystallized from silicate liquids at high pressures and temperatures provide more precise information on the pressures and temperatures reached during a shock event on the parental asteroid. The kinetics of phase transitions and diffusion of trace elements permit meaningful estimates of the pressure, temperature, and shock durations. We also present information on new dense minerals (C and TiO2) in terrestrial shocked rocks in impact craters and discuss their relevance to a reliable estimate of pressure and temperature conditions.

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GSA Special Papers

Advances in High-Pressure Mineralogy

Eiji Ohtani
Eiji Ohtani
Institute of Mineralogy, Petrology, and Economic Geology, Faculty of Science, Tohoku University, Sendai 980-8578, Japan
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Geological Society of America
Volume
421
ISBN print:
9780813724218
Publication date:
January 01, 2007

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