Major magmatic and metamorphic events in the Trans-North China Orogen: A geochemical and geochronological synthesis

Abstract

The Trans-North China Orogen (TNCO) was a Paleoproterozoic collisional belt along which the Eastern and Western Blocks amalgamated to form the North China Craton. Recent structural, geochemical and isotopic data show that the orogen was an Andes- or Japanese-type arc at the western margin of the Eastern Block, which was separated from the Western Block by an old ocean, with eastward-directed subduction. At 2550–2520 Ma, the subduction caused partial melting of the medium-lower crust, producing granitoid plutons in the granite-greenstone terranes. At 2530–2520 Ma, subduction of the oceanic lithosphere caused partial melting of the mantle wedge, forming greenstone-type mafic-felsic volcanic assemblages. Extension driven by widespread volcanism led to the development of back-arc basins in the orogen. At 2520–2475 Ma, the subduction caused further partial melting of the lower crust to form large amounts of TTG gneisses. In the Paleoproterozoic, episodic granitoid magmatism occurred, forming 2360 Ma, ~2250 Ma 2110-21760 Ma and ~2050 Ma granites and volcanics in the orogen. At 2150–1920 Ma, the subduction of an oceanic ridge led to emplacement of mafic dykes that were subsequently metamorphosed to high-pressure granulites. At 1880-1820 Ma, the closing of the ocean led to the continentarc-continent collision, which caused large-scale thrusting and isoclinal folds and formed HP granulites or eclogites. Peak metamorphism was followed by exhumation/uplift, resulting in widespread development of symplectic textures in the rocks. This study was financially supported by a China NFSC grant (40730315) and the Hong Kong RGC grants (7055/05P, 7063/06P and 7066/07P).