Neoproterozoic(750–711 Ma) Tectonics of the South Qinling Belt, Central China: New Insights from Geochemical, Zircon U-Pb Geochronological, and Sr-Nd Isotopic Data from the Niushan Complex

The Xiejiaba and Fuqiangbei plutons form part of the newly identified Neoproterozoic Niushan complex, which is located in the southern South Qinling belt(SQB). The plutons are compositionally similar, were emplaced at 750–711Ma, and provide insights into Neoproterozoic tectonism within the South Qinling belt. The Xiejiaba pluton contains diorite,quartz diorite, granodiorite, and granite phases, all of which are sub-alkaline and have variable major element compositions with negative correlations between SiO2and MgO, TFe2O3, Al2O3, CaO, TiO2and P2O5. These rocks are enriched in light rare earth elements(LREEs) and large ion lithophile elements(LILEs) and have negative Nb, Ta, P and Ti anomalies, all of which are indicative of arc-type magmatism. The Fuqiangbei pluton contains granitoids that are compositionally similar to the rocks in the Xiejiaba pluton. Samples from these plutons have similar εNd(t) values(1.24–5.99) but very variable(87Sr/86Sr)i values(0.7010–0.7054). Combining these data with the geochemical data for these rocks suggests that the magmas that formed the Niushan complex were derived from the crust–mantle boundary. This, combined with the results of previous research, suggests that the transition from low pressure-low temperature to low pressure-high temperature conditions within a subduction zone caused melting during a period of late subduction and backarc extension. This constrain the timing of subduction within the South Qinling belt and the northern Yangtze Block(YB) to 750–711 Ma, with this Neoproterozoic subduction associated with an ocean to the north overprinting an existing continental rift-type tectonic setting within the northern margin of the Yangtze Block and the South Qinling belt.