Granulite facies middle-lower crustal xenoliths from Nushan alkali basalt in northeastern Anhui Province, China

Abstract

Metamorphic xenoliths within the Nushan alkali basalt of northeastern Anhui (NEA), China, are from the middle-lower crust. They could be divided into two end-members: basic and acid. Intermediate xenoliths are scarcely found. Basic two-pyroxene granulites (pyriclasites) were formed at 720–810° C and 7–8 kb. Petrological and geochemical studies indicate that the primary magma of the protoliths of basic granulites was derived from the metasomatized upper mantle, while the parental magma of the acid end-member was probably produced by partial melting of the basic rocks. The protoliths of charnockites and grey gneisses represent respectively the early and late crystallization products of the granitic magma. The Nushan granulites are much different in many aspects from the granulites exposed in the northern part of North China, which implies the inhomogeneity regarding to the early evolution of the North China terrane.