Late Paleoproterozoic post-collisional bimodal magmatism in the North China Craton: Insights from the Miyun gabbro-granite suite

Abstract

Abstract Following the final cratonization of the North China Craton (NCC) through the assembly of major crustal blocks, the craton witnessed post-collisional magmatism during late Paleoproterozoic with the formation of diverse types of magmatic suites in the western and eastern margins of the Trans-North China Orogen (TNCO). Here, we investigate the anorogenic granitoid and associated gabbro from the Miyun complex located at the eastern margin of the TNCO. We present petrology, geochemistry, and zircon U-Pb, and Lu-Hf data on these rocks. The granite pluton is composed of a rapakivi phase with almost totally digested mafic magmatic enclaves, whereas the granite phase hosts gabbroic enclaves. The granitoids show high SiO2 content (71.28 to 78.83\xa0wt%), with peraluminous A2 type affinity and within plate (rift-related) features. The magmatic zircon grains from the granite yielded 207Pb/206Pb weighted mean age of 1696\xa0Ma. A similar crystallization age of 1683\xa0Ma for the gabbro indicates coeval bimodal magmatism. Both rocks carry zircon xenocrysts with older ages that are consistent with the magmatic and metamorphic events recorded from the basement rocks. The eHf(t) values of the zircon grains from the granitoid are markedly negative (−7.9 to −5.0) with two-stage Hf crustal model ages (TC DM) ranging from 2688\xa0Ma to 2855\xa0Ma, indicating the involvement of Mesoarchean to Neoarchean crustal components in the magma source. In contrast, the zircon grains from gabbro show both positive and negative eHf(t) values, suggesting magma derivation from depleted mantle sources with minor juvenile crustal component. We envisage that lower crustal melting induced by mantle-derived mafic magmas during post-collisional rifting generated felsic magmas, into which the mafic magma was injected, resulting in magma mixing and mingling. In conjunction with the information from post-collisional magmatic suites in the adjacent locations including gabbro-anorthosite complex, and similar aged magmatic complexes within the TNCO, we propose a major post-collisional magmatic event in the NCC which involved extensive mantle upwelling and lower crustal melting.