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

Lithological, structural, metamorphic and geochronological data for the Nor th China Craton enable its division into the Western and Eastern Blocks of Archean to Paleoproterozoic age separated by a north-south trending Paleopr oterozoic orogenic belt: the Central Zone. The Central Zone is divisible in to 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 are and intra-arc basin environments borderi ng the western margin of the Eastern Block. The basement rocks from the Cen tral Zone, regardless of their protolith age, composition and metamorphic g rade, record a metamorphic history characterized by nearly isothermal decom pression (M-2) and then retrogressive cooling (M-3) following peak metamorp hism (M-1). The decompression textures are represented by worm-like hyperst hene + plagioclase symplectites or clinopyroxene + orthopyroxene + plagiocl ase coronas in mafic granulites, hornblende/cummingtonite + plagioclase sym plectites in amphibolites, and cordierite coronas and cordierite + orthopyr oxene or cordierite + spinel symplectites in pelitic rocks. The cooling tex tures are shown by hornblende + plagioclase symplectites in mafic granulite s, chlorite + epidote + mica retrogressive rims around garnet or hornblende grains in amphibolites, and biotite + K-feldspar +/- muscovite +/- magneti te replacing garnet, cordierite and sillimanite in pelitic gneisses. These textural relations and their P-T estimates define near-isothermal decompres sional clockwise P-T paths, which, in combination with lithological, struct ural and geochronological constraints, are in accord with collision between the Eastern and Western Blocks of the North China Craton at similar to 1.8 Ga. (C) 2000 Elsevier Science B.V. All rights reserved.