The heart of China revisited, I. Proterozoic tectonics of the Qin mountains in the core of supercontinent Rodinia

摘要

The Qinling-Dabie orogenic collage, central China, constitutes the geographic, geologic, and cultural heart of China; it plays a key role in understanding the amalgamation and breakup of the Rodinia supercontinent and the subduction and exhumation of continental crust under ultrahigh-pressure conditions. Herein, we investigate the Proterozoic evolution of the Qinling-Dabie orogenic collage and surrounding segments of the bounding South China craton (SCC) and North China craton (NCC), employing published and new U/Th-Pb geochronology. The Kongling, Hong'an-Dabie, and Douling-Foping complexes constitute the nucleus of the Yangtze block, recording a common ～2.0 Ga orogenic event that integrated the Yangtze block into the supercontinent Columbia. The ～1.10-0.95 Ga Miaowan "ophiolite"-Shennongjia arc association of the Huangling dome-Shennongjia massif seems to have split and reassembled that nucleus. It formed earlier than or contemporaneously with the Sibao orogeny along the southeastern margin of the Yangtze block. The ～0.95-0.80 Ga Mian-Lue complex comprises an oceanic accretionary wedge that formed outboard of an associated fore-arc-arc system represented by the Bikou-Hannan-Micangshan massifs along the north (western) margin of the Yangtze block. The Qinling complex, currently sandwiched between the SCC and NCC, lacks pre-Mesoproterozoic cratonal basement, and its igneous rocks intruded a ～1.7-1.0 Ga old clastic wedge that incorporates meta-basites; it might have been part of the extended passive margin of East Antarctica and/or Australia. Neoproterozoic Qinling-complex magmatism spanned ～260 Myr and evolved from partial melting of the thick clastic sequence over an arc to a rift setting; most Qinling-complex paragneisses are erosional products of these igneous rocks. The ～1.0-0.85 Ga Qinling-complex magmatism formed independently from that along the north(west)ern Yangtze-block margin, but its ～0.8-0.7 Ga magmatism, peaking at ～750Ma, is widespread throughout the Yangtze block; this suggests post- ～825 Ma accretion of the Qinling complex to the Yangtze block. The Daba and Wudang Shan, Douling, and Hong'an-Dabie areas of the northern Yangtze block are dominated by ～0.8-0.6 Ga bimodal continental-rift igneous rocks; in accordance with similar ages in the Qinling complex and the entire SCC, continental rifting appears to have been most active at ～750 Ma. Our Rodinia scenario suggests that the Qinling-Dabie orogenic collage records the final stages of the assemblage of the core of Rodinia, and this was completed not earlier than ～825 Ma, and its breakup, which was most active at ～750 Ma.