Discussion on Mesozoic Geochemical Characteristics and Genesis of Nadanhada Terrane

Through field geological survey and drilling exploration in Sanjiang Basin, combined with geochemical analysis, the tectonic thermal evolution history of intrusive rocks is studied. The results show that the Early Mesozoic siliceous rocks in Qianjin Depression of Sanjiang Basin are widely distributed. The siliceous rocks are of post diagenetic hydrothermal metasomatic origin, and the hydrocarbon source rock indicators are good, which is expected to be a new formation for oil and gas exploration in Sanjiang area. The time temperature thermal history simulation of fission track shows that there have been two rapid cooling events (late Early Cretaceous Late Cretaceous and Paleocene Eocene) in the Nadanhadaling area since the Mesozoic era, with cooling rates of 3.42~4.81 ℃/Ma and 1.43~1.83 ℃/Ma, respectively. The two rapid cooling processes were caused by the subduction of the Pacific plate. The rapid cooling during the Early Cretaceous to the Late Cretaceous was caused by the change of the subduction direction of the Pacific plate and the collision and superposition of the Okot Motsk block and the East Asian continental margin; The rapid cooling from Paleocene to Eocene was mainly caused by the subduction and retreat of the Pacific plate, which made the East Asian continental margin in an extensional environment and caused denudation and cooling in most parts of Northeast China.