Evolution of Dunites in the Uralian Platinum Belt: Effects of Chemical, Temperature, and Oxygen Factors

摘要

Dunite bodies of two structural types have been established in the Uralian Platinum Belt (UPB): (1) cores of large autonomous (isolated) dunite-clinopy-roxenite bodies unrelated to gabbro and (2) small tectonic lenses (deformed fragments of large bodies) in the layered dunite-pyroxenite-gabbro complex (hot melange). At all dunite/pyroxenite contacts, the "primary" dunite with Mg# 0.94-0.92 is metasomati-cally replaced by a continuous series of olivine rocks varying from Fe-rich dunite (metadunite) to olivinite with Mg# 0.75 and less.The smaller the body, the greater portion of its section is occupied by metaso-matic zones, i.e., the body dimension and Mg# value show a positive correlation. The smallest bodies are completely composed of metadunite and olivinite.