Sodium-metasomatism of Ca-Al-rich inclusions in the anomalous carbonaceous chondrite Ningqiang

概要

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A petrographic and mineralogical study of Ningqiang reveals that a significant proportion of the Ca-Al-rich inclusions (CAIs) consist entirely of fine-grained porous aggregates, and melilite in them has been extensively replaced by nepheline. Small fragments of nepheline-bearing inclusions and fine nepheline grains are widely scattered in the matrix. We found evidence suggesting that those fine-grained porous inclusions were formed by replacing primary Type A CAIs and spinel-pyroxene type CAIs. The results suggest that Ningqiang has experienced extensive Na-metasomatism on its parent body. In that process, part of CAIs became fine-grained porous, and during subsequent brecciation, they were disaggregated and segregated from the original portion in the parent body. We infer that these processes may be responsible for the low abundances of CAIs and bulk refractory lithophiles that are characteristic of Ningqiang.
日本鉱物科学会の論文
2009-10-01