Metamorphism of basement rocks in the Central Zone of the North China Craton: implications for Paleoproterozoic tectonic evolution

Abstract

Lithological, structural, metamorphic and geochronological data for the North China Craton enable its division into the Western and Eastern Blocks of Archean to Paleoproterozoic age separated by a north–south trending Paleoproterozoic orogenic belt: the Central Zone. The Central Zone is divisible into a series of low- to medium-grade granite–greenstone belts and high-grade metamorphic terrains containing reworked Archean material and late Archean to Paleoproterozoic juvenile igneous and sedimentary rocks which developed in intra-continental magmatic arc and intra-arc basin environments bordering the western margin of the Eastern Block. The basement rocks from the Central Zone, regardless of their protolith age, composition and metamorphic grade, record a metamorphic history characterized by nearly isothermal decompression (M 2) and then retrogressive cooling (M 3) following peak metamorphism (M 1). The decompression textures are represented by worm-like hypersthene+plagioclase symplectites or clinopyroxene+orthopyroxene+plagioclase coronas in mafic granulites, hornblende/cummingtonite+plagioclase symplectites in amphibolites, and cordierite coronas and cordierite+orthopyroxene or cordierite+spinel symplectites in pelitic rocks. The cooling textures are shown by hornblende+plagioclase symplectites in mafic granulites, chlorite+epidote+mica retrogressive rims around garnet or hornblende grains in amphibolites, and biotite+K-feldspar±muscovite±magnetite replacing garnet, cordierite and sillimanite in pelitic gneisses. These textural relations and their P–T estimates define near-isothermal decompressional clockwise P–T paths, which, in combination with lithological, structural and geochronological constraints, are in accord with collision between the Eastern and Western Blocks of the North China Craton at ∼1.8 Ga.