摘要：

Composition of coexisting ortho- and Ca-pyroxene or pigeonite may be used to estimate the temperature of crystallization at low to moderate pressures by solving the equation: RT ln X/sub Mg--M1//sup Cpx/ X/sub Mg--M2//sup Cpx/ ..gamma../sub Mg--M2//sup Cpx/ = RT ln ..cap alpha../sub Mg--Opx/ - 500 where R is gas content, T temperature in /sup 0/K to be estimated, X/sub Mg--M1//sup Cpx/ the site of occupancy of Mg on the site M1 or M2 in clinopyroxene (Cpx), ..gamma.. the M2 site activity coefficient and ..cap alpha../sub Mg--Opx/ the activity of Mg in orthopyroxene. A non-ideal model for the M2 site in both the pyroxenes is used to obtain the activity composition relations. The site occupancy data in orthopyroxene are available in the literature. The site occupancy data in clinopyroxene are obtained by using compositional data on three coexisting pyroxenes by using the condition that in such coexisting pyroxenes the intracrystalline equilibrium constants are simply related. Using the activity--composition data, the equation may be solved graphically or by using a computer to match the two sides of the equation at various assumed temperatures. The temperature estimates must be based on an accurate compositional analysis of several samples. It is expected that further

展开