Superposition of Cretaceous and Cenozoic deformation in northern Tibet: A far-field response to the tectonic evolution of the Tethyan orogenic system

Abstract

Although the Cenozoic Indo-Asian collision is largely responsible for the formation of the Tibetan plateau, the role of pre-Cenozoic structures in controlling the timing and development of Cenozoic deformation remains poorly understood. In this study we address this problem by conducting an integrated investigation in the northern foreland of the Tibetan plateau, north of the Qilian Shan-Nan Shan thrust belt, NW China. The work involves field mapping, U-Pb detrital-zircon dating of Cretaceous strata in the northern foreland of the Tibetan plateau, examination of growth-strata relationships, and construction and restoration of balanced cross sections. Our field mapping reveals multiple phases of deformation in the area since the Early Cretaceous, which was expressed by northwest-trending folding and northwest-striking thrusting that occurred in the early stages of the Early Cretaceous. The compressional event was followed immediately by extension and kinematically linked right-slip faulting in the later stage of the Early Cretaceous. The area underwent gentle northwest-trending folding since the late Miocene. We estimate the magnitude of the Early Cretaceous crustal shortening to be ∼35%, which we interpret to have resulted from a far-field response to the collision between the Lhasa and the Qiangtang terranes in the south. We suggest that the subsequent extension in the Early Cretaceous was induced by orogenic collapse. U-Pb dating of detrital zircons, sourced from Lower Cretaceous sedimentary clasts from the north and the south, implies that the current foreland region of the Tibetan plateau was a topographic depression between two highland regions in the Early Cretaceous. Our work also shows that the Miocene strata in the foreland region of the northern Tibetan plateau was dominantly sourced from the north, which implies that the rise of the Qilian Shan did not impact the sediment dispersal in the current foreland region of the Tibetan plateau where this study was conducted.

Tectonic Deformation of an Intraplate Orogenic Belt: Mesozoic Sedimentary Basins in the Northeastern Qilian Shan, China

“…However, the deformation style of the Yumu Shan remains unclear. It has been proposed that the Yumu Shan klippes were derived from the nappe system of the NQT (Wang et al, 2021); however, we postulate that the Yumu Shan was controlled by the YMT-S to form the southward thrust system, thereby leaving the LMK in the basin.…”

“…The Cenozoic strata in the northern Qaidam basin may source from Qilian Shan and the southern Qaidam Basin (Lu et al, 2018), and it indicates that the strata materials in the Qaidam Basin are severed by the northern Qaidam thrust belt (Cheng et al, 2021). According to the source trace of the Lower Cretaceous strata, the ages of the Cretaceous strata are consistent with those of the basement rocks in the Alashan area and in the North China Block (Wang et al, 2021) and most of the materials in the northern Sunan Basin originate from the Bei Shan (Cheng et al, 2019a), indicating that the Alashan Block had a higher topography during the Mesozoic than the current location of the Qilian Shan.…”

“…In the Sunan Basin, the thrust fault system trends almost NW-SE as the fold hinges. In the eastern portion of the Yumu Shan (S-4 and S-5) near the Liyuanpu Fault (LYF) (Wang et al, 2021), the fold hinge has a ~133 °trend and a ~23 °plunge that is right-laterally rotated by ~13 °. In the northern aspect of the Sunan Basin (S-1), the fold hinge trends almost W and has a 15 °plunge that has been left-laterally rotated ~25 °from the NW.…”

“…Prior to the Cretaceous, crustal shortening of the craton in the Alashan Block thrust downward into the northern Qilian Shan (Yin and Harrison, 2000;Zuza et al, 2016). Two phases of N-S tectonic extension (Chen et al, 2003) formed rifted basins or topographic depressions (Wang et al, 2021) in the Sunan and Huangcheng basins, which resulted from the evolution of the suture belt. The rifted basins were then filled with Cretaceous and Neogene strata.…”

“…Additionally, two phases of continental collision occurred in the central Qilian Shan before the Cretaceous (Zuza et al, 2019). It is believed that the northern Qilian Shan region formed higher topography than the central Qilian Shan region during the Mesozoic (Wang et al, 2021). Moreover, based on reports from the Bureau of Mineral Resources of Gansu Province (BMRGP, Regional Geological Survey) (1982), Bureau of Mineral Resources of Inner Mongolia Province (BMRIMP, Regional Geological Survey) (1991) and Bureau of Mineral Resources of Qinghai Province (BMRQP, Regional Geological Survey) (1991), it is clear that the data pertaining to the geometry of the faults and strata constitute the geological background, while the relationships between the faults and folds remains unclear.…”