Least squares technique to the P-T estimation of ultramafic rocks involving olivine, orthopyroxene and garnet

Abstract

The mathematical background has been established to evaluate the equilibrium pressure and temperature of ultramafic xenolith by the application of least squares technique to the equilibrium among olivine, orthopyroxene and garnet. Estimated pressures in the approximated system SiO₂-Al₂O₃-FeO-MgO-CaO are slightly greater than those in the additional correction of Mn-Ni-Cr-Ti for the granular type of lherzolites and are shifted to lower pressure sides for the sheared lherzolites. The inflection in the paleogeotherm beneath northern Lesotho is observed at the depths 150 km.