Petrography and mineral compositions of the Yamato-7308 howardite

• Main Authors: Ikeda,Yukio, Takeda,Hiroshi
• Format: Report
• Language: English
• Published: Department of Earth Sciences, Faculty of Science, Ibaraki University/Mineralogical Institute, Faculty of Science, University of Tokyo 1984
• Subjects: The ''Y''; Yamato; Memoirs of National Institute of Polar Research; Polar Research
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=1722; http://id.nii.ac.jp/1291/00001722/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=1722&item_no=1&attribute_id=18&file_no=1

The constituents of the Y-7308 howardite are classified into four groups : holocrystalline lithic clasts, hypocrystalline to holohyaline materials, mineral fragments and matrix. The holocrystalline lithic clasts include four clans : (1) A diogenitic cumulate type consisting of diogenitic clasts. (2) A eucritic cumulate type consisting of hypersthene-eucritic clasts and coarse-grained inverted pigeonite-eucritic clasts. (3) A Na-rich magma type consisting of fine-grained inverted pigeonite-eucritic clasts. (4) A Na-poor magma type consisting of pigeonite-eucritic clasts and fayalitic olivine-hedenbergitic pyroxene-tridymite-plagiolcase clasts. Most clasts of hypocrystalline to holohyaline materials were probably formed by shock events from breccias and/or regoliths similar in composition to the whole rock of Y-7308. Most mineral fragments were probably derived by shocks from complete disaggregation of holocrystalline lithic clasts and hypocrystalline to holohyaline materials. Magnesian olivine and orthopyroxene fragments may have been derived from dunitic or orthopyroxenitic rocks whose clasts cannot be observed in Y-7308.