THE INTERPLAY BETWEEN CLIMATE AND TECTONICS DURING THE UPWARD AND OUTWARD GROWTH OF THE QILIAN SHAN OROGENIC WEDGE, NORTHERN TIBETAN PLATEAU

The driving mechanism of the northward growth of the Qilian Shan, which occupies a transition zone between the ~4500 m high central Tibetan plateau and the adjacent <2500 m high cratons to the northeast, figures prominently into debates of orogenic wedge evolution. In this study, we integrate new detrital zircon geochronological data with seismic profiles and drill core data from the NE Qaidam and Suganhu basins to investigate the mountain building of the Qilian Shan as well as the source to sink relationship between the Qilian Shan and adjacent basins. Despite intensive crustal shortening within the Qilian Shan during the deposition of Lulehe to Shangganchaigou Fm. (Eocene to Oligocene) as shown on the seismic profiles, stratigraphic evidence reveals a northward retrogradation of coarse deposits in the Qaidam basin. In parallel, detrital zircon geochronology suggest that the southern Qilian Shan served as a significant source for the sediments in both the NE Qaidam basin and the Suganhu basin during the deposition of Lulehe to Shangganchaigou Fm. The connection between the NE Qaidam and the Suganhu basin, as well as the southern Qilian Shan was finally cut off in the Miocene. Combining published reginal climate records with provenance data from Cenozoic strata in the Qaidam basin, we infer that increased precipitation and glacial meltwater inflow under relatively warm climate conditions drove basin-scale transgression during the deposition of the Lulehe Fm. to Shangcganchaigou Fm. Since then, the Qaidam basin has been gradually isolated in response to the intensified deformation within the surrounding mountain belts and regional aridification. Collectively, we propose that climate driven erosion defeated the tectonic thickening in the southern Qilian Shan prior to the Miocene and caused the Qilian Shan wedge to stall. Deformation remained localized in the southern Qilian Shan as wedge taper continued to build. Since the Miocene, decreased erosion of the wedge under arid to semi-arid conditions has allowed deformation to maintain a high enough wedge taper to allow for northward propagation of the deformation front into the central and northern Qilian Shan. This study highlights the significant influence of climate in upward and outward growth in the northern Tibetan plateau.