Permian tectonic evolution and continental accretion in the eastern Central Asian Orogenic Belt: A perspective from the intrusive rocks

The tectonic evolution and history of continental accretion of the eastern Central Asian Orogenic Belt (CAOB) are not yet fully understood. In this study, we investigate Permian intrusive rocks from the Jiamusi Block of the eastern CAOB to constrain the tectonic evolution and continental accretion of this region during the late-stage evolution of the Paleo-Asian Ocean. Our new data show that Early Permian gabbro-diorites were derived from the partial melting of depleted mantle metasomatized by oceanic-slab-released fluids. Middle Permian adakitic granites have low Na₂O and MgO and high K₂O contents, indicating a thickened-lower-crust source. Late Permian S-type granites were derived from the partial melting of continental crust. A compilation of the available geochronological data for Permian intrusive rocks (including adakitic and A-, S-, and I-type granites and mafic rocks) from the eastern CAOB reveals that the A-type granites formed mainly during the Early–Middle Permian, S-type and adakitic granites mostly during the Middle–Late Permian, and I-type granites and mantle-derived mafic rocks throughout the Permian. The A-type granites, which are proposed to have been sourced from thinned continental crust, indicate an extensional setting in the eastern CAOB during the Early Permian. The Middle–Late Permian adakitic granites imply a thickened continental crust, which indicates a compressional setting. Therefore, the eastern CAOB underwent a transition from extension to compression during the Middle Permian, which was probably triggered by the late-stage subduction of Paleo-Asian oceanic crust. Considering the petrogenesis of the intrusive rocks and inferred regional tectonic evolution of the eastern CAOB, we propose that vertical underplating of mantle- and oceanic-slab-derived magmas contributed the materials for continental crust accretion.