A preliminary study of Rb-Sr systematics and trace element abundances on impact-melted LL-chondrites from Antarctica
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概要
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Rb-Sr systematics, REE, Ba, Sr, Rb, K, Ca and Mg abundances were analyzed in 1) whole-rock samples from 8 Antarctic LL-chondrites including 4 impact-melted rocks and 2 non-Antarctic LL chondrites, and 2) 8 mineral separates from one of the impact-melted meteorites, Y-790964. In a ^<87>(Rb)-^<87>(Sr) evolution diagram, analyses from the severely shocked meteorites deviate from the 4.5 b. y.-evolution line although those of normal LL-chondrites are plotted on or close to the line, suggesting a late thermal evolution of these impact-melted meteorites. Analyses of mineral separates and a whole-rock from Y-790964 yield a Rb-Sr internal isochron age of 1197±54 (2σ) m. y. and an initial ^<87>(Sr)/^<87>(Sr) ratio of 0.73160±0.00028 (2σ). This age is the youngest known among impact-related materials in brecciated meteorites. In addition, the impact-melted meteorites have somewhat higher and fractionated REE, Sr, Rb and K abundances compared with normal LL chondrites. The 1.2 b. y. age is interpreted as a time of melting induced by intense impacts on the LL-chondrite parent body, accompanied by REE, Rb/Sr and K fractionations. Therefore, we suggest that strong impact and regolith processes on the LL-chondrite parent body never ceased until at least 1.2 b. y. ago.
- 国立極地研究所の論文
著者
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NAKAMURA NOBORU
Department of Earth and Planetary Sciences, Kobe University
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Nakamura N
Graduate School Of Science And Technology Kobe University
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Nakamura Noboru
Graduate School Of Science And Technology Kobe University
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Misawa Keiji
Department of Earth & Planetary Sciences, Faculty of Science, and Division of the Nature of the Eart
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Misawa K
Department Of Earth And Planetary Sciences Faculty Of Science Kobe University
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Okano Osamu
Department of Geosciences, Faculty of Science, Okayama University
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Honma Hiroji
Institute for Thermal Spring Research, Okayama University
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Goto Hiroya
Laboratory of Geosciences,College of Liberal Arts, Kobe University
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Okano O
Department Of Geosciences Faculty Of Science Okayama University
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Okano Osamu
Department Of Earth Sciences Okayama University
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Goto Hiroya
Laboratory Of Geosciences College Of Liberal Arts Kobe University
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Honma Hiroji
Institute For Thermal Spring Research Okayama University
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Nakamura Noboru
Department Of Earth & Planetary Sciences Kobe University
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Nakamura Noboru
Department Of Earth & Planetary Sciences Faculty Of Science And Division Of The Nature Of The Ea
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