Late Cenozoic river system reorganization and its origin within the Qilian Shan, NE Tibet

Abstract

The northward growth of the Tibetan Plateau has reshaped the Qilian Shan Orogen with prolonged history along two large strike-slip faults, the Altyn Tagh Fault on the west and the Haiyuan Fault on the east. This orogen with its high elevation is referred to as the “Water Tower” of the northeastern margin of the Tibetan Plateau, shedding many rivers into the surrounding arid areas in a way different from all other orogens within the plateau. The factors that control the evolution of these rivers in this highly active region, particularly their relative contribution through time, are not well known. Our study presents evidence that the left-lateral movement of the Haiyuan Fault (one of the largest active strike-slip faults within the Tibetan Plateau since ~13–8 Ma) created a series of NW-trending linear thrust-fold belts, aligned in an en echelon pattern along the trace of the fault. This completely reconfigured the flow direction of the rivers within the Qilian Shan Range: from N-S rivers that flowed into the Hexi Corridor and Qaidam Basin, to today's W-E rivers flowing into the Tarim Basin and Longxi Basin, along a series of NW-trending linear thrust-folds belt, aligned in an en echelon pattern along the trace of the Haiyuan Fault on the north and south. This river system reorganization event is corroborated by sedimentary and geochronologic evidence within the intermountain basins where these rivers flow. The Longxi Basin, the largest intermountain basin surrounding the Qilian Shan on the east, was drained by rivers flowing east, which were dammed by the uplift of the Liupan Shan since ~10–8 Ma to form a large lake. The second river system reorganization again occurred through climate change in ~1.8 Ma. It included the incision of the Yellow River capturing major rivers and halting their flow to the southeast. It is concluded that the Haiyuan Fault plays a crucial role not only in the lateral growth of the Tibetan Plateau but also in the uplift of the Qilian Shan, which led to the river system reorganization.