Cenozoic tectonic development in the northeastern Tibetan Plateau: Evidence from thermochronological and sedimentological records

The northeastern Tibetan Plateau occupies the northernmost portion of the plateau, whose timing and pattern of deformation during its Cenozoic tectonic development provide constraints on the kinematics and dynamics of plateau formation and evolution of Asian climate. Our knowledge of the tectonic growth in the northeastern Tibetan Plateau has progressed immensely over the past decades, particularly the last decade, and thus calls for a review on the tectonic history recorded by mountain building and adjacent basin deposition. Although evidence for the Paleocene-Eocene deformation exist in the northeastern Tibetan Plateau, some of them remain questionable as indicated by recently published high-quality magnetostratigraphies and thermochronological data. The Paleogene crustal shortening, if occurred, may have been confined to the Qaidam Shan and West Qinling. Updated paleomagnetostratigraphies from the northern Qaidam Basin indicate that crustal shortening did not initiate until the Oligocene, but not soon after the India-Eurasia collision, if the deposition of the conglomerates from the Lulehe Formation can be attributed to tectonic origin. We highlight that more investigations are needed to verify the reliability and areal extent of the Paleogene crustal shortening in the northeastern Tibetan Plateau. Furthermore, more recent studies suggest that the middle-Miocene deformation is widely distributed across the Qilian Shan. Based on a synthesis of studies on deformation timing and pattern in the Qilian Shan and its adjacent foreland basins, such as the Hexi Corridor and northern Qaidam Basin, we indicate that the Qilian Shan underwent a phase of approximately synchronous deformation during the middle Miocene. Since then, the crustal deformation has progressively propagated outward, including northward into the Hexi Corridor and Gobi-Alxa Block, southward into the northern Qaidam Basin, and eastward along the left-lateral strike-slip QilianHaiyuan fault. The summarized spatiotemporal growth appears to preclude widespread collision-age deformation or monotonical northward migration of crustal shortening in the northern interior of the plateau. The synchronous middle-Miocene deformation across the Qilian Shan could be a consequence of progressive northward growth of the plateau or a far-field effect of mantle lithosphere removal that occurred in the southern or middle portion of the plateau. Since the middle-Miocene crustal deformation is widespread around the margins of the plateau, we suggest that the removal of the mantle lithosphere beneath the southern or middle portion of the plateau may be the most plausible dynamic mechanism.