New shock-induced transformations of olivines in Martian meteorites

Details New shock-induced transformations of olivines in Martian meteorites New shock-induced transformations of olivines in Martian meteorites

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmmr54a..07r&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #MR54A-07

Physics

3900 Mineral Physics, 3944 Shock Wave Experiments, 5420 Impact Phenomena, Cratering (6022, 8136), 5709 Composition (1060), 6022 Impact Phenomena (5420, 8136)

Scientific paper

Transient high pressures and temperatures generated during the impact of meteors or asteroids on planetary surfaces can induce phase transformations in low-pressure minerals that mimic those occurring at depth within the silicate mantle of terrestrial planets. For olivine, phase transitions to the high-pressure polymorphs wadsleyite and ringwoodite are observed in shocked chondrites. Melting transitions have also been reported in some samples. We have investigated the transformations of the olivine presenting an unusually black color in two newly-described Martian meteorites NWA2737 and NWA1950. The shock conditions were not sufficient to cause melting or transformation into the high-pressure polymorphs. The black color of the olivines is due to the presence of Fe-Ni metallic nanoparticles that result from loss of oxygen during the shock event. Raman spectroscopy and high-resolution transmission electron microscopy indicate that the shocked "olivines" have a hexagonal close-packed (hcp) structure similar to that observed in the metastable transformations of olivine at high pressure and low temperature, and of wadsleyite at low pressure and moderate temperatures. We propose a metastable phase diagram of olivine including a new hcp phase that accounts for the observations in natural samples and the experimental results.

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