Department of Polar Science, School of Mathematics and Physics, The Graduate University for Advanced Studies/Antarctic Meteorite Research Center, National Institute of Polar Research/Antarctic Meteorite Research Center, National Institute of Polar Research/Antarctic Meteorite Research Center, National Institute of Polar Research
抄録(英)
Allan Hills (ALH-) 77252 is a regolith breccia consisting of various types of clasts differing in metamorphic grades (L3-6). Titanium/aluminum ratios of low-Ca pyroxene in ALH-77252 are bimodally distributed. In equilibrated clasts, Ti/Al ratios of low-Ca pyroxene are ∿0.5 which are quite different from those in unequilibrated clasts of ∿0.07. Among equilibrated and unequilibrated clasts, the Ti/Cr ratio of low-Ca pyroxene also shows large differences. Because titanium and aluminum are not diffusive elements in the pyroxene crystal structure, diffusional redistribution of titanium and aluminum in low-Ca pyroxene requires significantly higher metamorphic temperature than Fe-Mg homogenization, possibly above ∿800℃. Alternatively, if the source materials of L-group chondrites were initially different, the fingerprints of mineral properties resistant to thermal metamorphism remain unchanged. If this was the case, the distinctly higher Ti/Al ratios of low-Ca pyroxene in equilibrated clasts originated from the primary signatures of low-Ca pyroxene prior to thermal metamorphism.
Minor element chemistry of low-Ca pyroxene in Allan Hills-77252, an L3-6 regolith breccia
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KJ00000041004
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概要
