关键词: 蒙古—鄂霍茨克构造域, 中生代演化, 锆石U-Pb年代学, 地球化学, 地壳厚度重建, 漠河盆地, 古太平洋

Abstract: In order to unravel the spatiotemporal processes and dynamic mechanisms underlying Mesozoic multi-plate convergence in East Asia, this study focuses on the Mongol-Okhotsk tectonic domain—a critical region. By elucidating its Mesozoic tectonic evolutionary history as a vital component of the eastern segment of the Central Asian orogenic belt, this research seeks to provide constraints for reconstructing the interactions between regional plates. This study investigates the northern Heihe area of Northeast China through systematically integrating published zircon U-Pb chronology and whole-rock geochemical data of Mesozoic magmatic and sedimentary rocks, combined with detailed analysis of the sedimentary sequence in the Mohe basin, reconstructing the Late Mesozoic tectonic evolution history of this area. The present results show that the Mesozoic strata and magmatic activities in this area have comprehensively recorded the tectonic evolution process of the Mongol-Okhotsk tectonic domain from subduction, collision to post-collision extension. Zircon geochronology constrains the depositional age of the Emurhe Group in the Mohe basin to the Late Jurassic-Early Cretaceous (160-140 Ma), with the peak volcanic activity phase occurring at 125-110 Ma during the Early Cretaceou. Geochemical characteristics reveal a progressive transition of the magma sources from active continental margin arc settings to post-collisional extensional regimes. Quantitative crustal thickness reconstruction reveals an oscillatory “N” evolutionary trend (thickening-thinning-re-thickening), corresponding to three distinct geodynamic processes: subduction-related compression (~40 km), collision collapse (~35 km), and subsequent superimposed modification (~40 km). The Mongol-Okhotsk Ocean has undergone a temporally diachronous “scissor-like” closure process, with the middle section terminating during the late Middle Jurassic (~165 Ma) while the eastern section persisted until the early Early Cretaceous (~145 Ma). Following this collisional event, whole area transitioned into post-orogenic extension, subsequently overprinted by far-field effects of the Paleo-Pacific plate subduction. This study provides new evidence for understanding the ocean-continent transition process in the Mongol-Okhotsk tectonic domain and its mutual influence with the Paleo-Pacific tectonic domain.

Key words: Mongol-Okhotsk tectonic domain, Mesozoic evolution, zircon U-Pb chronology, geochemistry, crustal thickness reconstruction, Mohe basin, Paleo-Pacific