Yamato-791093, a metal-sulfide-enriched H-group chondritic meteorite transitional to primitive IIE irons with silicate inclusions

摘要

The Y-791093 meteorite consists of volumetrically equal amounts of metal-sulfide-rich and chondritic portions. The chondritic portion is texturally and mineralogically similar to H6 chondrites. The metal-sulfide-rich portion consists mainly of kamacite and troilite; chondritic fragments, including silicate grains and chondrules, are common. The entire assemblage of the metal-sulfide-rich portion is texturally similar to the primitive IIE irons with chondritic inclusions such as Netschaevo and Techado, but richer in sulfide component. The chondritic, sulfide, and metallic components were analysed by INAA, and compared with average compositions of H chondrites and Netschaevo. The chondritic portion has the same composition as that of average H chondrite. The abundances of siderophile and chalcophile elements in the metal-sulfide-rich portion estimated from the compositions of metallic and sulfide components are similar to those of average H chondrite and Netschaevo, except for higher chalcophiles and a lower Ir content than average H chondrite. The metal-sulfide-rich portion of Y-791093 crystallized from Fe-Ni-S melt produced by shock melting of H chondrites, and Y-791093 was formed by mixing of the Fe-Ni-S melt with H6 chondritic material, near the surface of an H-group chondrite parent body. We conclude that Y-791093 is a transitional member between H chondrites and primitive IIE irons with silicate inclusions.