Petrology of Yamato-75261 meteorite: An enstatite (EH) chondrite breccia

• Main Author: Hiroko Nagahara
• Format: Report
• Language: English
• Published: Geological Institute, Faculty of Science, University of Tokyo 1991
• Subjects: Antarctic; Clayton; Yamato; Antarc*
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=4542; http://id.nii.ac.jp/1291/00004542/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=4542&item_no=1&attribute_id=18&file_no=1

Yamato-75261 is a breccia with a non-porphyritic clast embedded in the partly porphyritic matrix. The clast consists mainly of closely packed finegrained enstatite with interstitial material rich in Al. Metallic iron and troilite are rare. An anomalous Fe-Mn-Mg-Ca-Cr monosulfied, of which composition lies intermediate between alabandite in EL chondrites and niningerite in EH chondrites, occurs in the interstices of the clast. The heterogeneous matrix consists of enstatite, forsterite, glass, fine-grained materials, and rare troilite. Chemical compositions of bulk meteorite, clast, and matrix obtained by the broad beam analysis of a microprobe are highly fractionated. Both the clast and matrix are especially depleted in siderophile elements, which is in accordance with apparent depletion of metallic iron over the thin section. Aluminum, Fe, Na, Si, Ca, and S are enriched in the matrix portion; on the contrary, Mg is enriched in the clast. Texture, mineral assemblage, and mineral compositions along with oxygen isotopic compositions (T. K. MAYEDA and R. N. CLAYTON; Papers presented to the 14th Symposium on Antarctic Meteorites, Tokyo, Natl Inst. Polar Res., 172,1989) suggest that Y-75261 is a breccia related to enstatite chondrites. The CaO content of enstatite, Ni, Si, and P contents of kamacite, and Ti and Cr contents of troilite indicate a closer affinity to EH chondrites than to EL's in spite of the intermediate composition of the sulfide.