Mineralogy of Antarctic aubrites, Yamato-793592 and Allan Hills-78113: Comparison with non-Antarctic aubrites and E-chondrites

• Main Authors: Makoto Kimura, Yang-Ting Lin, Yukio Ikeda, Ahmed EL Goresy, Keizo Yanai, Hideyasu Kojima
• Format: Report
• Language: English
• Published: Department of Earth Science, Faculty of Science, Ibaraki University/Institute of Geochemistory, Academica Sinica/Department of Earth Science, Faculty of Science, Ibaraki University/Max-Planck Institute fur Kernphysik/National Institute of Polar Research/National Institute of Polar Research 1993
• Subjects: Allan Hills; Antarctic; The Antarctic; Yamato; Antarc*
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=4610; http://id.nii.ac.jp/1291/00004610/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=4610&item_no=1&attribute_id=18&file_no=1

Two Antarctic aubrites, Yamato (Y)-793592 and Allan Hills (ALH)-78113,were mineralogically studied, for comparison with minerals in non-Antarctic aubrites and enstatite chondrites. The Antarctic aubrites are breccias consisting of coarse-grained enstatite fragments and fine-grained matrix. ALH-78113 has 200-300μm dark clasts that are fine-grained aggregates of silicate and opaque minerals. FeO-rich pyroxene (up to Fs_<21>) occurs in the dark clasts. One dark clast has K-feldspar. These dark clasts seem to be exotic inclusions with distinct mineralogy. Daubreelite in the two Antarctic and non-Antarctic aubrites is lower in Zn than those in EH3-5 chondrites. This reflects the depletion of volatile elements in aubrites. Hydrated Na-Cr-sulfides were also found. Djerfisherite is a common accessory mineral in aubrites. It is characterized by low contents of Cu and Na, and high content of Ni, in comparison to djerfisherite in EH3-5 chondrites. Y-793592 has many roedderite grains. The occurrences of roedderite, Na-Cr-sulfides and djerfisherite in aubrites suggest that Al_2O_3 relative to alkali elements may have been fractionated during nebular or magmatic process.