Composite nature of the North China Granulite-Facies Belt: Tectonothermal and geochronological constraints

Abstract

Granulite-facies rocks are intermittently exposed in a roughly E–W trending belt that extends for approximately 2000 km across the North China Craton, from the Helanshan, Qianlishan, Wulashan–Daqingshan, Guyang and Jining Complexes in the Western Block, through the Huai'an, Hengshan, Xuanhua and Chengde Complexes in the Trans-North China Orogen, to the Jianping (Western Liaoning), Eastern Hebei, Northern Liaoning and Southern Jilin Complexes in the Eastern Block. The belt is generally referred to as the North China Granulite-Facies Belt, previously interpreted as the lowest part of an obliquely exposed crust of the North China Craton. Recent data indicate that the North China Granulite-Facies Belt is not a single terrane. Instead, it represents components of three separate terranes: the Eastern and Western Blocks and Trans-North China Orogen. Each of these units records different metamorphic histories and reflect the complex tectonic evolution of the NCC during the late Archean and Paleoproterozoic. Mafic granulites in the Eastern Block and the Yinshan Terrane (Western Block) underwent medium-pressure granulite-facies metamorphism at about ∼2.5 Ga, with anticlockwise P–T paths involving near isobaric cooling following peak metamorphism, reflecting an origin related to intrusion and underplating of mantle-derived magmas. Pelitic granulites in the Khondalite Belt (Western Block) underwent medium-pressure granulite-facies metamorphism at about 2.0–1.9 Ga, with clockwise P–T paths, which record the Paleoproterozoic amalgamation of the Yinshan and Ordos Terranes to form the Western Block. Mafic and pelitic granulites in the Trans-North China Orogen experienced high- to medium-pressure granulite-facies metamorphism at ∼1.85 Ga, with clockwise P–T paths involving nearly isothermal decompression following peak metamorphism, which are in accord with the final collision between the Eastern and Western Blocks to form the North China Craton at ∼1.8 Ga. The NCGB cannot therefore represent a separate unique terrane; instead it reflects the amalgamation of three separate granulite terranes that evolved independently and at different times.