Magmatic inclusions in martian meteorites

概要

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Magmatic inclusions in martian meteorites occur mainly within olivine and pyroxene grains. They are a few hundreds of micrometers to less than 10 micrometers across in size and have various mineral assemblages. They are grouped into five types on the basis of their silicate mineral assemblages, from glassy inclusions of type I to kaersutite-bearing inclusions of type V. The types of magmatic inclusions in shergottites reflect cooling rates of their host lithologies. The compositions of glasses in magmatic inclusions have a wide range, even if they occur within a single grain of olivine or pyroxene. The wide compositional range of the glasses in magmatic inclusions is caused by metastable crystallization of the residual melts; some magmatic inclusions crystallize only wall olivine, although some crystallize pyroxene, a silica mineral, plagioclase, or kaersutite in addition to wall olivine. The wide compositional range of glasses and the variety in texture and mineral assemblages of magmatic inclusions seem to be controlled by cooling rates of the host lithology, nucleation processes of the minerals, chemical compositions of the residual melts, and so on. The chemical trends of residual melts in magmatic inclusions are explained by using a pseudoternary phase diagram of quartz-olivine-plagioclase.
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