Tectonic setting of Cretaceous basins on the NE Tibetan Plateau: Insights from the Jungong basin
Quantifying the Cenozoic growth of high topography in the Indo‐Asian collision zone remains challenging, due in part to significant shortening that occurred within Eurasia before collision. A growing body of evidence suggests that regions far removed from the suture zone experienced deformation before and during the early phases of Himalayan orogenesis. In the present‐day north‐eastern Tibetan Plateau, widespread deposits of Cretaceous sediment attest to significant basin formation; however, the tectonic setting of these basins remains enigmatic. We present a study of a regionally extensive network of sedimentary basins that are spatially associated with a system of SE‐vergent thrust faults and are now exposed in the high ranges of the north‐eastern corner of the Tibetan Plateau. We focus on a particularly well‐exposed basin, located ∼20 km north of the Kunlun fault in the Anyemaqen Shan. The basin is filled by ∼900 m of alluvial sediments that become finer‐grained away from the basin‐bounding fault. Additionally, beds in the proximal footwall of the basin‐bounding fault exhibit progressive, up‐section shallowing and several intraformational unconformities which can be traced into correlative conformities in the distal part of the basin. The observations show sediment accumulated in the basin during fault motion. Regional constraints on the timing of sediment deposition are provided by both fossil assemblages from the Early Cretaceous, and by K–Ar dating of volcanic rocks that floor and cross‐cut sedimentary fill. We argue that during the Cretaceous, the interior NE Tibetan Plateau experienced NW–SE contractional deformation similar to that documented throughout the Qinling–Dabie orogen to the east. The Songpan‐Ganzi terrane apparently marked the southern limit of this deformation, such that it may have been a relatively rigid block in the Tibetan lithosphere, separating regions experiencing deformation north of the convergent Tethyan margin from regions deforming inboard of the east Asian margin.