Petrological Study of Martian Meteorites

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The petrological study on Martian meteorites was carried out in details. Especially it was stressed to investigate the occurrence and to clarify the genesis of magmatic inclusions that occur in Martian cumulative and basaltic shergottites. Magmatic inclusions in Martian meteorites are very small with about 10-100 micrometers across, and occur in phenocrystic minerals (olivine and pyroxene). They consist mainly of olivine, fassaite, plagioclase, a silica mineral, or Kaersutite in addition to igneous glass, and are very important because they have direct information on their parent magmas and formational conditions. Two lherzolitic (cumulative) shergottites (ALH77005 and Yamato-793605) have a nearly same mineral assemblage, although the two show slightly different lithologies. They may have been produced from Martian parent magmas that have chemical compositions similar to a typical basaltic meteorite (the shergotty meteorite). It was also clarified that magmatic inclusions occurring in olivine in the lherzolitic meteorites are different in mineral assemblages and mineral compositions from those in pyroxene. This difference may be due to their different stages of magmatic fractional crystallization. Kaersutite was found o to occur in the two lherzolitic shergottites, and the water vapor pressure of their coexisting magmas was estimated to be less than 1 kilo bars. Magmatic inclusions in basaltic shergottites (DaG735, and so on) also were surveyed in details. They differ in mineral assemblage from those in the lherzolitic shergottites, and seem to have crystallized on a meta-stable condition. The DaG735 may have formed as a cumulative basaltic lithology, which contains a large number of phenocrystic olivine in a basaltic melt.