Antarctic howardites and their primitive crust

• Main Authors: Hiroshi Takeda, Hiroshi Mori, Yukio Ikeda, Teruaki Ishii, Keizo Yanai
• Format: Report
• Language: English
• Published: Mineralogical Institute, Faculty of Science, University of Tokyo/Mineralogical Institute, Faculty of Science, University of Tokyo/Department of Earth Sciences, Faculty of Science, Ibaraki University/Ocean Research Institute, University of Tokyo/National Institute of Polar Research 1984
• Subjects: Antarctic; Yamato; Antarc*; Memoirs of National Institute of Polar Research; Polar Research
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=1719; http://id.nii.ac.jp/1291/00001719/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=1719&item_no=1&attribute_id=18&file_no=1

Lithic clasts and mineral fragments in Yamato-79 howardites, Y-790727,Y-791208 and Y-791492 have been investigated by optical microscopy, electron microprobe and single crystal X-ray diffraction. These howardites are chemically intermediate between ordinary diogenites and eucrites, and distinct from Y-7308. Some lithic clasts are also intermediate in mineralogy between endmember diogenites and eucrites, including a cumulate eucrite clast with a partly inverted pigeonite, an ordinary eucrite-like gabbroic clast intermediate in chemical composition between cumulate eucrites and ordinary eucrities, and an augite rich clast with a silica mineral. A partial melting model and fractional crystallization models have been compared to account for these new howardites, and models involving two-stage process are proposed. These howardites may have been products of excavation by an impact or impacts shallower than that for Y-7308 but deeper than those for polymict eucrites.