A dark inclusion in the Manych LL (3.1) ordinary chondrite: A product of strong shock metamorphism

概要

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A dark inclusion (MNC-1) from the Manych LL (3.1) chondrite contains elliptical objects ("augen"; 50-500μm in long axis) embedded in a fine-grained matrix. Most augen are composed of parallel intergrowths of fine laths of Fe-rich olivine, high-Ca pyroxene, and Na-rich feldspathic glass that commonly enclose coarse grains (5-80μm in diameter) of Fe-rich olivine (Fo_<62-83>). The matrix of MNC-1 consists predominantly of interlocking, granular grains (<1-10μm in diameter) of Fe-rich olivine (Fo_<63-66>), interstitial high-Ca pyroxene and Na-rich feldspathic glass. Both the Manych host and MNC-1 have experienced strong shock metamorphism. The texture and mineralogy of MNC-1 suggest that the matrix of MNC-1 experienced shock melting, whereas the "augen" represent unmelted precursor material. Bulk major element composition of MNC-1 is generally similar to the average values for LL chondrites, except that MNC-1 is considerably depleted in S and enriched in FeO. The large S depletion may be due to volatilization during impact-induced melting. Texture and mineralogy of the augen are distinct from those of the Manych host, so MNC-1 may not be a melt dike which formed in situ in the host rock. MNC-1 appears to be a xenolith that solidified elsewhere on the LL chondrite parent body and was later incorporated to the present location.
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