HR: 1340h
AN: MR43B-1234    [Abstracts]
TI: Shock Metamorphism of L6 Chondrites Sahara 98222 and Yamato 74445: the P-T Conditions and the Shock age
AU: * Ozawa, S
EM: ozawasin@ganko.tohoku.ac.jp
AF: Institute of Mineralogy, Petrology and Economic Geology, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan
AU: Ohtani, E
EM: ohtani@mail.tains.tohoku.ac.jp
AF: Institute of Mineralogy, Petrology and Economic Geology, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan
AU: Suzuki, A
EM: a-suzuki@mail.tains.tohoku.ac.jp
AF: Institute of Mineralogy, Petrology and Economic Geology, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan
AU: Miyahara, M
EM: miyahara@ganko.tohoku.ac.jp
AF: Institute of Mineralogy, Petrology and Economic Geology, Graduate School of Science, Tohoku University, Sendai, 980-8578, Japan
AU: Terada, K
EM: terada@hiroshima-u.ac.jp
AF: Department of Earth and Planetary System Sciences, Hiroshima University, Higashi- Hiroshima, 739-8526, Japan
AU: Kimura, M
EM: makotoki@mx.ibaraki.ac.jp
AF: Institute of Astrophysics and Planetary Science, Faculty of Science, Ibaraki University, Mito, 310-8512, Japan
AB: Impact phenomena are the fundamental processes of accretion of the terrestrial planets. Therefore, investigations of meteorites that experienced shock events are useful for understanding mechanisms of planetary impact events and formation of terrestrial planets. Heavily shocked meteorites contain abundant shock melt veins, where some high-pressure minerals have been discovered. In this study, we investigated mineralogy of shock melt veins of two L6 chondrites (Sahara 98222 and Yamato 74445) and estimated the P-T conditions during their impact events.
We found that the shock melt veins of these meteorites contain several high-pressure minerals such as wadsleyite, jadeite and tuite for Sahara 98222 and ringwoodite (+ wadsleyite), akimotoite and lingunite for Yamato 74445. Tuite is a high-pressure polymorph of whitlockite and lingunite is a high-pressure polymorph of albite with hollandite structure. Based on mineralogy in the shock veins; we estimated the pressure and temperature conditions during their impact events: 13-15 GPa, > 2000°C for Sahara 98222 and 15- 24 GPa, > 2200°C for Yamato 74445, respectively.
We also conducted a U-Pb dating of phosphates in and around the shock melt veins of Sahara 98222 using a Sensitive High Resolution Ion Micro Probe (SHRIMP-II) at Hiroshima University to reveal when this shock event occurred. We obtained following radioactive ages: Pb-Pb isochron age: 4466 ± 31 Ma; U-Pb isochron age: 4498 ± 150 Ma; Total U-Pb isochron age: 4467 ± 22 Ma. These ages seem to be slightly younger than the previously reported ages of chondrites, which are usually older than 4500 Ma. This could suggest that Sahara 98222 have recorded a shock event in the very early stage of the solar system where the planetary formation was going on.
DE: 1160 Planetary and lunar geochronology
DE: 3654 Ultra-high pressure metamorphism
DE: 3662 Meteorite mineralogy and petrology (1028, 6240)
DE: 6022 Impact phenomena (5420, 8136)
DE: 6240 Meteorites and tektites (1028, 3662)
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting