Chrome‐rich clinopyroxene in orthopyroxenite from Maowu, Dabie Mountains, central China: A second record and its implications for petrogenesis

Abstract

A second occurrence of chrome‐rich clinopyroxene has been discovered as inclusions in orthopyroxene in orthopyroxenite from Maowu, the Dabie Mountains, Central China. The average formula for chrome‐rich clinopyroxene can be expressed as (Na 0.39 Ca 0.54 ) 0.93 (Mg 0.57 Fe 2+ 0.06 Fe 3+ 0.01 Cr 0.24 Al 0.15 ) 1.03 Si 2.02 O 6 , with a maximum amount of kosmochlor component of 28.52 mol%. The unit cell parameters obtained from a single‐crystal are a = 9.614 Å, b = 8.800 Å, c = 5.240 Å, β = 106.59°, space group C2 / c . The indices of refraction are α = 1.697, β = 1.704, γ = 1.726. Chrome‐rich clinopyroxene, which coexists with chromite, chromian rutile and chromian pyrope, crystallized at a temperature of 1025 °C and very high pressure, and therefore represents a mantle relic. Together with the appearance of low‐pressure inclusion mineral assemblage and the estimation of physical–chemical conditions for matrix minerals, the Maowu eclogite–ultramafic complex is considered to be formed during ultrahigh‐pressure metamorphism from the mantle‐derived protolith.