Early Permian bimodal magmatism and tectonic evolution of the easternmost Paleo-Asian orogenic system.

Late Paleozoic tectonic evolution of northeastern China is complicated by the interaction of the Central Asian Orogenic belt development and the initiation of subduction from the Pacific Ocean plate along the eastern margin of Asia. In this study, we elucidate this problem by collecting new geochemical and geochronological data from late Paleozoic bimodal igneous rocks from the eastern margin of the Jiamusi block. By LA–ICP–MS zircon U–Pb dating, the 206Pb/238U age of the granitoid sample is 313–279 Ma, and the diabase 206Pb/238U age is 298–276 Ma. Rock geochemical studies show that diabase and granitoid have obvious chemical differentiation characteristics, indicating that they are the products of non-homologous magmatic evolution. Zircon Lu–Hf isotopes indicate that diabase magma originates from the metasomatism of the mantle wedge by subducting oceanic crust melts, granitoid magma mainly comes from the lower crust and the new crust. Our results together with a synthesis of existing data show that bimodal magmatism occurred in the study area from the Late Carboniferous to Early Permian when the Jiamusi block was an active continental margin and in a stretching background. Our synthesis of the existing data places our new data into a regional tectonic framework, and our proposed tectonic model provides the following new insights: (1) the northward expansion of the Paleo-Tethys Ocean from the Late Carboniferous to the Early Triassic led to the overall northward drift of the Paleo-Asian Ocean and the Xing'an-Mongolian Orogenic belt, which marks the easternmost segment of the Central Asian Orogenic belt, (2) the Paleo-Asian Ocean continued Late Permian–Early Triassic subduction caused back extension that rifted the Jiamusi and Songnen blocks apart and formed the Mudanjiang Ocean. [ABSTRACT FROM AUTHOR]