Geochemistry of metaanorthosites from a greenstone belt in Karnataka, India
Sheet-like fine-grained metaanorthosite bodies occur in the 3.5–3.2 Ga greenstone belt of Holenarasipur, Karnataka, India. These bodies are associated with metaperidotitic komatiites, serpentinites, and amphibolites. In texture, grain size, major, and trace element composition, including rare-earth elements (REE), they resemble lunar anorthositic basalts and anorthositic microgabbros. On the basis of these resemblances, similar trends of geochemical evolution of the earth and moon during their early history are indicated. It is suggested that after the accretion of the earth, high temperature conditions might have existed to generate magmas enriched in Ca–Al at or near the surface which resulted in the formation of anorthite-rich basaltic and peridotitic lavas. The incomplete cumulation of the anorthite before and during the extrusion of the ultrabasic lava appears to have given rise to sheet-like anorthosite layers between the metaperidotitic and basaltic komatiites.