Interpretative Mineral Chemistry of Ultramafic Rocks of Chalk Hills, Tamil Nadu

The ultramafic rocks of Chalk Hills near Salem, comprise dunite, wehrlite and olivine clinopyroxenite in association with mafic alkaline rocks. The constituent phases of the ultramafics have been analysed and their compositional data have been evaluated to assess petrogenetic factors. Dunite appears to be restite formed through mantle melting whereas wehrtite and olivine clinopyroxenite represent successive progressive cumulation products from transported high magnesian melt. Mineral chemistry of mafic phases and compositional interrelation between them indicates an equilibration temperature of 1022° to 1088°C for wehrtite and a relatively lower temperature level (ca 900°C) for olivine clinopyroxenite. It appears that the extracted high magnesian melt generating the wehrlite and olivine clinopyroxenicte cumulates, equilibrated at shallower level near base of the crust under ca 11 kb pressure.