Early Cretaceous foreland-like Northeastern Qaidam Basin, Tibetan Plateau and its tectonic implications: Insights from sedimentary investigations, detrital zircon U–Pb analyses and seismic profiling
Abstract The Early Cretaceous collision between the Lhasa and Qiangtang terranes is one of the critical tectonic events that shaped the southern margin of the Eurasian continent, and that impacted the formation of the Cenozoic Tibetan Plateau. However, how far north this collision affected the structural and sedimentary geology of the Early Cretaceous remains uncertain. To address this issue, we present results from an integrated study of Lower Cretaceous strata in the Northeastern Qaidam Basin (NEQB), northern Tibetan Plateau, based on field observations, detrital zircon U–Pb analyses, and seismic profile interpretations. The Lower Cretaceous mainly consists of deltaic, fluvial, and alluvial sandstone and conglomerate with a pattern of orogeny-related molasse deposits and a provenance in the nearby South Qilian Shan to the north. A number of south-directed reverse faults developed and formed piggy-back basins in the Early Cretaceous. These reverse faults remained active and affected erosion during the Late Cretaceous, leaving an unconformity above the Cretaceous strata. These observations indicate a foreland-like NEQB due to the uplift and southward thrusting of the South Qilian Shan in the Early Cretaceous. We further interpreted the NEQB and the South Qilian Shan to be the northern edge of the compressional regime associated with the Lhasa-Qiangtang collision in the Early Cretaceous, which contrasts with the contemporaneous extensional setting in the North Qilian Shan and further north. We also observed that some Early Cretaceous faults were rejuvenated as major thrusts in the South Qilian Shan thrust belt in the Cenozoic. For the first time, this study maps the northern boundary of the Late Mesozoic Qiangtang Plateau and highlights a protracted influence on Tibetan Plateau tectonism since the Early Cretaceous.