A unique omphacite, amphibole, and graphite-bearing clast in Queen Alexandra Range (QUE) 99177: A metamorphosed xenolith in a pristine CR3 chondrite

作者: Neyda M. Abreu

DOI: 10.1016/J.GCA.2012.11.041

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摘要: Abstract A metamorphosed, unshocked, chondritic clast, containing approximately equal volumes of matrix and chondrules, has been identified in the primitive CR3 chondrite QUE 99177. The most striking features this clast are presence ferroan omphacitic pyroxenes, amphiboles (pargasite pargasitic hornblende) coarse-grained (up to 70 μm) graphite laths. also contains relatively equilibrated FeO-rich olivine, low-Ca pyroxene, sulfides (pentlandite troilite). clast’s coarse, interlocking crystals. chondrules extensively recrystallized, contain no mesostasis or metal, present poorly-defined boundaries. Based on its compositional crystallographic features, omphacite appears have formed at high pressures (>6 GPa). Amphibole formation probably postdated occurred by reaction clinopyroxene, an oxidizing, Na-rich fluid temperatures (>700 °C). absence metal suggests that was rich S.

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