Discovery of Middle-Late Devonian and Early Permian magmatic events in East Asia and their implication for the Indosinian Orogeny in south China; insights from the sedimentary record

Whether the driver of the Indosinian orogeny in the South China block was related to the evolution of the Paleotethyan Ocean or the Paleo-Pacific Ocean has been a point of much debate. We applied detrital zircon U-Pb dating to Permian-Triassic sedimentary rocks from South China to trace sediment provenance and to further test these models. Our results, combined with other published data from the Pingxiang, Youjiang, Yong'an, and Yongding Basins, show that 400-350 Ma and 300-260 Ma zircon grains are ubiquitous throughout the entirety of southern South China. This indicates regional magmatic events as potential sources. The discovery of Middle-Late Devonian and Early Permian igneous rocks, tuffs, and volcaniclastic rocks in Southeast Asia and Hainan Island implies the presence of two magmatic events (400-350 Ma and 300-260 Ma) within or beyond the southern margin of South China. This information, together with the mostly negative epsilon Hf(t) values of 400-350 Ma and 300-260 Ma zircon grains, arc-like geochemical signatures of the possible source rocks, and the regional geology of East Asia, suggests that they originated from sources related to Paleotethyan and even Proto-Tethyan subduction. Thus, Permian-Triassic sedimentation and the Indosinian orogeny in South China were largely controlled by the evolution of the Tethyan Ocean.