Shocked plagioclase in the lunar meteorites Yamato-793169 and Asuka-881757: Implications for their shock and thermal histories

スポンサーリンク

概要

• 論文の詳細を見る

• Yamato (Y)-793169 and Asuka (A)-881757 are unbrecciated lunar mare meteorites that contain shocked plagioclase as a main constituent phase. Plagioclase in Y-793169 is composed of fine-grained microlitic grains that preserve the overall optical orientation of the original grain. Small vesicles are also observed within plagioclase grains. Plagioclase shows chemical zoning from the An-rich core (An_<96>) to the An-poor rim (An_<85>). These observations suggest that plagioclase in Y-793169 recrystallized from a diaplectic glass by thermal annealing as the heating experiment of a diaplectic plagioclase suggests. The thermal annealing event might occur sometime later than 750Ma that has been derived from the K-Ar study of plagioclase. A-881757 plagioclase has completely transformed into an isotropic glass similar to "maskelynite" in Martian meteorites. Chemical zoning of plagioclase is well preserved, showing a systematic change of composition from the An-rich core (An_<95>) to the slightly An-poor rim (An_<90>). Plagioclase glass partly converts to crystalline (optically single crystal) plagioclase near the fusion crust due to reheating during the atmospheric entry. All of these observations suggest that plagioclase glass in A-881757 is probably a diaplectic glass. Unlike Y-793169,plagioclase glass in A-881757 has not been modified by later thermal events, which is consistent with the old ^<40>Ar-^<39>Ar age (3.8Ga) of A-881757 plagioclase glass. Thus, Y-793169 and A-881757 contained (A-881757 still contains) a diaplectic plagioclase glass that was shock-induced perhaps during the late heavy bombardment of the Moon as their old crystallization ages (3.8-3.9Ga) indicate.

• 国立極地研究所の論文

著者

• Mikouchi Takashi

  Mineralogical Institute Graduate School Of Science University Of Tokyo

関連論文

• Mineralogical consideration of possible microfossils in martian meteorite ALH84001
• Mineralogical study of angrite Asuka-881371: Its possible relation to angrite LEW87051
• Evaluation of diffusion coefficients of Fe-Mg and Ca in olivine
• Mineralogical comparison of Hammadah al Hamra 126 with some ureilites
• Yamato-793605: A new lherzolitic shergottite from the Japanese Antarctic meteorite collection
• Shocked plagioclase in the lunar meteorites Yamato-793169 and Asuka-881757: Implications for their shock and thermal histories
• Cooling rates of olivine xenocrysts in the EET79001 shergottite
• Chemical zoning of olivines in the Yamato-791717 CO3 chondrite
• Diffuse reflectance spectra for heated samples of an H5 chondrite: Importance of oxygen fugacity at heating

スポンサーリンク