The Onset of Thermal Metamorphism in Enstatite Chondrites



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Five E chondrites, Kota Kota, Parsa, Qingzhen, Sahara 97096, and Yamato 60091, were studied to determine if Cr in olivine is useful as an indicator of thermal metamorphism. E chondrites are important because they are the only meteorites to have an oxygen isotopic composition similar to that of the Earth and Moon and thus may be analog material from which the Earth formed. They are also the most reduced chondrites. The redistribution of Cr in olivine during thermal metamorphism is studied with the petrographic microscope, scanning electron microscope (SEM) and electron microprobe (EMP). The conclusions of this study are 1) Cr in olivine is a good indicator of the early onset of thermal metamorphism in E chondrites, 2) olivine in E chondrites can be used to find the most primitive E chondrites, 3) the petrological types of five meteorites in this study are ordered from most to least primitive: Y-60091, SAH 97096, Parsa, Kota Kota, Qingzhen, and 4) during thermal metamorphism, Cr is redistributed into metal and sulfide phases in and around olivine grains.