Late Permian Bimodal Volcanic Rocks in the Northern Qiangtang Terrane, Central Tibet: Evidence for Interaction Between the Emeishan Plume and the Paleo-Tethyan Subduction System

Many studies provide compelling evidence for a fossil mantle plume beneath the Late Permian Emeishan large igneous province located near the southeastern margin of the central Tibetan Plateau, a region associated with the Paleo-Tethyan subduction system. However, little is known about whether direct plume-subduction interaction occurred during the Late Permian. Here we report geochronological, mineralogical, geochemical, and Sr-Nd-Hf-O isotopic data for the Late Permian (similar to 259-256 Ma) bimodal volcanic rocks (BVRs) in the northern Qiangtang Terrane (NQT), central Tibet. These BVRs consist mainly of basalts, rhyolites, and rhyolitic tuffs. The rhyolites with A-type affinity were generated by partial melting of newly underplated basalts. Geochemical and isotopic data suggest that two components (ocean island basalt-type mantle and subducted sediment-derived fluid) were involved in the generation of the basalts in an extensional back-arc region. Considering the Permian tectonic evolution of the NQT, we propose that this enriched ocean island basalt-type mantle was distinct from the Paleo-Tethyan depleted upper mantle. It most likely originated from Emeishan-plume material that flowed westward from the South China Block to the nearby NQT, driven by slab rollback-induced counterflow. The presence of high-temperature A-type rhyolites in bimodal back-arc magmatism also indicates a special subduction setting influenced by a nearby plume. Thus, we propose that the Late Permian BVRs were the result of interaction between the Emeishan plume and the Paleo-Tethyan subduction system.