EQUILIBRIUM RELATIONS IN Mg-RICH PART OF THE PYROXENE QUADRILATERAL

Abstract

Coexisting inverted protoenstatite and bronzite from Cape Vogel, Papua (Dalwitz, Green & Thompson, 1966) were re-examined to obtain partition coefficient of Mg and Fe between contiguous protopyroxene and orthopyroxene. Stability relations of pyroxenes in the system MgSiO₃-FeSiO₃ are suggested mainly on the basis of the partition coefficients of Mg and Fe between natural coexisting protopyroxene and orthopyroxene and between natural coexisting orthopyroxene and Ca-poor clinopyroxene. The most probable isothermal sections in the Mg-rich part of the ternary system CaSiO₃-MgSiO₃-FeSiO₃ are presented.