Geothermometric and Oxygen Fugacity Studies of Mayurbhanj Basic Igneous Complex

The basic igneous complex of Mayurbhanj is a differentiated suite composed of harzburgite, gabbronorite, leucogabbronorite and anorthosite. EPMA of the coexisting oxides in the rock samples reveal that magnetite-ilmenite have re-equilibrated between 770°C and less than 500°C and fo₂, of 10_-16 to less than 10_-25. Ilmenite granules and thick lamellae have identical composition and approach pure FeTiO₃. The chrominn spinel-olivine geothermometry in harzburgite suggests a temperature of 1263°C. The pyroxene geothermometric data in gabbroic rocks indicate equilibration temperature range of 819° C to 1071° C. The thermometric data indicate that the magnetite and ilmenite equilibrated at lower temperature than the coexisting pyroxenes for a particular rock sample.