CHROME-RICH CLINOPYROXENE IN ORTHOPYROXENITE FROM MAOWU, DABIE MOUNTAINS, CENTRAL CHINA - A 2ND RECORD AND ITS IMPLICATIONS FOR PETROGENESIS

A second occurrence of chrome-rich clinopyroxene has been discovered a s inclusions in orthopyroxene in orthopyroxenite from Maowu, the Dabie Mountains, Central China. The average formula for chrome-rich clinopy roxene can be expressed as .3)9Ca(0.54))(0.93)(Mg(0.57)Fe(2+)0.06Fe(0. 01)(3+) Cr0.24Al0.15)(1.03)Si2.02O6, with a maximum amount of kosmochl or component of 28.52 mol%. The unit cell parameters obtained fi om a single-crystal are a = 9.614 Angstrom b = 8.800 Angstrom c = 5.240 Ang strom, beta = 106.59 degrees, space group C2/c. The indices of refract ion are alpha = 1.697, beta = 1.704, gamma = 1.726. Chrome-rich clinop yroxene, which coexists with chromite, chromian rutile and chromian py rope, crystallized at a temperature of 1025 degrees C and very high pr essure, and therefore represents a mantle relic. Together with the app earance of low-pressure inclusion mineral assemblage and the estimatio n of physical-chemical conditions for matrix minerals, the Maowu eclog ite-ultramafic complex is considered to be formed during ultrahigh-pre ssure metamorphism from the mantle-derived protolith.