Chronostratigraphic framework of late Mesozoic terrestrial strata in the Hailar-Tamtsag Basin, Northeast China, and its geodynamic implication

The Hailar-Tamtsag Basin (HTB), an important component of the late Mesozoic extensional basin system in Northeast (NE) China, is characterized by episodic rifting, dramatic magmatism, and thick terrestrial sediments, which provides crucial opportunities to understand late Mesozoic tectonomagmatic events in NE China. However, the previously established late Mesozoic chronostratigraphic framework in the basin remains problematic due to limited isotopic chronological constraints. Here, we present 28 new zircon U-Pb ages for the volcanic rocks from the HTB, which allow us to establish a refined chronostratigraphic framework for the late Mesozoic terrestrial strata. Newly calibrated results indicate that the depositional ages of the Tamulangou and Tongbomiao formations are constrained to ca. 157-148 and ca. 142-137 Ma, respectively; the depositional ages of the Lower Nantun and Upper Nantun members are constrained to ca. 131-120 and ca. 117-111 Ma, respectively. Combining these results with previous studies on sedimentation, structural deformation, and magmatism, the Late Jurassic-Early Cretaceous tectonostratigraphic evolution of the HTB is reconstructed, and three major phases of intracontinental deformation are identified. The HTB experienced extensional deformation in the Late Jurassic due to the break-off of the subducted oceanic slab of the Mongol-Okhotsk Ocean and subsequent gravitational collapse of orogenically thickened crust following the closure of the ocean basin. Then, in the latest Jurassic-earliest Cretaceous, the evolution of the HTB was dominated by compressional deformation related to flat-slab subduction of the Paleo-Pacific Plate. During the Early Cretaceous, an extensional regime resumed in the HTB in response to rollback of the subducting Paleo-Pacific Plate.