Initial uplift of the Qilian Shan, northern Tibet since ca. 25 Ma: Implications for regional tectonics and origin of eolian deposition in Asia

Abstract Sedimentary rocks in northern Tibet record uplift of the Tibetan Plateau and its potential connection with the evolution of the central Asian aridity, therefore offering a typical example of tectonic-climate linkage. The coarse-grained conglomeratic and sandy red beds of the Lulehe Formation (Fm.) in the northern Qaidam Basin (QB), northern Tibet, have long been held as synorogenic sediment accumulation. There is, however, a heated debate on its source area (the Qilian Shan, the east Kunlun Shan, or Qimen Tagh) and initiation age (ca. 52, 25.5, or ca. 21 Ma, respectively). These proposals lead to distinctly different mountain building processes of the giant Qilian Shan during the Cenozoic. One view argues that the Qilian Shan began to uplift substantially as a simultaneous far-field response to the India-Asia collision at 55–50 Ma. In contrast, others claim that significant rise of the Qilian Shan and thus northeastward expansion of the Tibetan Plateau did not occur until 19 or 12 Ma. Based on an updated magnetostratigraphic framework for the Cenozoic sediments in the northern QB, here we conducted structural, paleocurrent, pebble composition, zircon grain shape and surface texture, and detrital geochronological analyses of the Lulehe Fm., in the northern QB. The results indicate that the Lulehe Fm. was produced essentially by an initial rush of lithic clasts derived from the deformed Mesozoic sedimentary cover, which can be attributed to initial rise of the Qilian Shan since ca. 25 Ma. This finding leads additional credence to the argument that the onset of significant uplift of mountain ranges along the periphery of the plateau occurred nearly synchronously from the latest Oligocene through early Miocene. These prolonged elevated Mesozoic sediments covering the fold-thrust belts of the northern QB, on the other hand, may have acted as a sustained source of material for the Miocene eolian deposits in the western Chinese Loess Plateau.