Magnesium phosphates experienced high-temperature transition found on the CI-like carbonaceous chondrite Yamato 980115 by Raman microspectroscopy.

Abstract

Magnesium phosphate grains, minor accessory minerals found on the primitive meteorite Yamato 980115 (Y 980115), were investigated by Raman microspectroscopy. All magnesium phosphate grains found in the present study can be assigned to farringtonite, dehydrated magnesium phosphate Mg₃(PO₄)₂-I. Since the Mg₃(PO₄)₂-I is generally formed via the irreversible thermal transition from the polymorphs of Mg₃(PO₄)₂-II and -III at above 750-800 degree Celsius, we can infer that the parent body of the Y 980115 meteorites experienced thermal alteration with such a high temperature. This result is in good accordance with the previous studies and the proposals on the alteration history of Y 980115 by the electron-beam microscope and X-ray diffraction analyses. Furthermore, the hydrated form of the magnesium phosphates of Mg₃(PO₄)₂·4H₂O, Mg₃(PO₄)₂·8H₂O, and Mg₃(PO₄)₂·22H₂O was not found in the present research, also suggesting that the extensive vaporization of the hydrated water molecules with magnesium phosphate occurred by such high-temperature thermal alteration. Since Y 980115 has been historically categorized to heavily aqueously altered CI (Ivuna-type) carbonaceous chondrites but has distinct characteristic to CI meteorites, the present result would provide further evidence to the complexed alteration history of the parent body of Y 980115 meteorite.