TY - JOUR
T1 - Transformation textures, mechanisms of formation of high-pressure minerals in shock melt veins of L6 chondrites, and pressure-temperature conditions of the shock events
AU - Ozawa, Shin
AU - Ohtani, Eiji
AU - Miyahara, Masaaki
AU - Suzuki, Akio
AU - Kimura, Makoto
AU - Ito, Yoshinori
PY - 2009/11
Y1 - 2009/11
N2 - The high-pressure polymorphs of olivine, pyroxene, and plagioclase in or adjacent to shock melt veins (SMVs) in two L6 chondrites (Sahara 98222 and Yamato 74445) were investigated to clarify the related transformation mechanisms and to estimate the pressure-temperature conditions of the shock events. Wadsleyite and jadeite were identified in Sahara 98222. Wadsleyite, ringwoodite, majorite, akimotoite, jadeite, and lingunite (NaAlSi3O 8-hollandite) were identified in Yamato 74445. Wadsleyite nucleated along the grain boundaries and fractures of original olivine. The nucleation and growth of ringwoodite occurred along the grain boundaries of original olivine, and as intracrystalline ringwoodite lamellae within original olivine. The nucleation and growth of majorite took place along the grain boundaries or fractures in original enstatite. Jadeite-containing assemblages have complicated textures containing "particle-like," "stringer-like," and "polycrystalline-like" phases. Coexistence of lingunite and jadeite-containing assemblages shows a vein-like texture. We discuss these transformation mechanisms based on our textural observations and chemical composition analyses. The shock pressure and temperature conditions in the SMVs of these meteorites were also estimated based on the mineral assemblages in the SMVs and in comparison with static high-pressure experimental results as follows: 13-16 GPa, >1900 °C for Sahara 98222 and 17-24 GPa, >2100 °C for Yamato 74445.
AB - The high-pressure polymorphs of olivine, pyroxene, and plagioclase in or adjacent to shock melt veins (SMVs) in two L6 chondrites (Sahara 98222 and Yamato 74445) were investigated to clarify the related transformation mechanisms and to estimate the pressure-temperature conditions of the shock events. Wadsleyite and jadeite were identified in Sahara 98222. Wadsleyite, ringwoodite, majorite, akimotoite, jadeite, and lingunite (NaAlSi3O 8-hollandite) were identified in Yamato 74445. Wadsleyite nucleated along the grain boundaries and fractures of original olivine. The nucleation and growth of ringwoodite occurred along the grain boundaries of original olivine, and as intracrystalline ringwoodite lamellae within original olivine. The nucleation and growth of majorite took place along the grain boundaries or fractures in original enstatite. Jadeite-containing assemblages have complicated textures containing "particle-like," "stringer-like," and "polycrystalline-like" phases. Coexistence of lingunite and jadeite-containing assemblages shows a vein-like texture. We discuss these transformation mechanisms based on our textural observations and chemical composition analyses. The shock pressure and temperature conditions in the SMVs of these meteorites were also estimated based on the mineral assemblages in the SMVs and in comparison with static high-pressure experimental results as follows: 13-16 GPa, >1900 °C for Sahara 98222 and 17-24 GPa, >2100 °C for Yamato 74445.
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U2 - 10.1111/j.1945-5100.2009.tb01206.x
DO - 10.1111/j.1945-5100.2009.tb01206.x
M3 - Article
AN - SCOPUS:76749136784
VL - 44
SP - 1771
EP - 1786
JO - Meteoritics and Planetary Science
JF - Meteoritics and Planetary Science
SN - 1086-9379
IS - 11
ER -