Petrological and mineralogical study of enstatite chondrites with reference to their thermal histories

• Main Authors: Makoto Kimura, Yangting Lin
• Format: Report
• Language: English
• Published: Institute of Astrophysics and Planetary Science, Faculty of Science, Ibaraki University 1999
• Subjects: Antarctic; Yamato; Antarc*
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=5942; http://id.nii.ac.jp/1291/00005942/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=5942&item_no=1&attribute_id=18&file_no=1

We investigated the complicated thermal histories of 8 Antarctic enstatite chondrites. In this report we present results of our mineralogical and petrological studies. Three of them (Yamato (Y)-791790,791810 and 791811) are EH4 chondrites, but experienced higher temperature events in comparison with most of the other EH4s. Y-791790 includes a shock-induced melt vein. Y-86760 is recognized as a new EH melt rock that cooled rapidly from high temperatures. Absences of daubreelite in the EH4s and roedderite and forsterite in the melt rocks are consistent with such high temperature events. We infer that the parent body (or bodies) of EH chondrites experienced heavy impacts after or during metamorphism. Some EH4s and melt rocks cooled rapidly from high temperatures near the surface of the parent body, whereas the others cooled slowly in the depth of the parent body or were later reheated. Y-791510 contains glassy matrix unusually enriched in CaO, in the interstices among enstatite grains. The opaque mineralogy of Y-791510 is inconsistent with that of EH or EL. We propose that Y-791510 represents a new grouplet of enstatite chondrites.