Petrology of silicate inclusions in the Miles IIE iron

概要

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The Miles IIE iron contains many silicate inclusions with gabbroic and cryptocrystalline textures. The gabbroic inclusions consist of inverted pigeonite, orthopyroxene, high-Ca pyroxene, olivine, sodic plagioclase, antiperthite, K-feldspar, tridymite, granitic glass, chromite, rutile, armalcolite, ilmenite, whitlockite, chlorapatite, troilite, schreibersite, taenite, and kamacite. They are the crystallization products of silicate melts which were produced by equilibrium or impact partial melting of an H chondritic precursor, and the degree of melting was variable, but about 25% on the average. Partial melting probably took place in a regolithic breccia on an H chondritic parent body. The melts experienced reduction during their crystallization. The cryptocrystalline inclusions consist mainly of cryptocrystalline albite and alkali feldspar, and sometimes have phenocrystic clinopyroxene, needles of orthopyroxene, and/or whitlockite-predominant nodules. Some nodules include P-bearing magnesian olivine, sodalite, and rutile, and these nodules appear to have separated as P_2O_5-rich melts from the albite-rich melt by liquid immiscibility. The inclusions cooled rapidly, resulting in their cryptocrystalline textures.
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