Stratigraphic record of tectonic and climatic impact on orogenic growth: An example from the Hexi Corridor Basin, NE Tibetan Plateau

The locus of shortening, accretion, and erosion are key components in modulating the rate, pattern, and magnitude of orogenic wedge growth, but separating their respective roles in the evolution of wedge taper is often difficult because of the absence of exhumation and uplift data from the mountains. However, such information can be preserved in the adjacent basins, and a combination of sediment provenance and accumulation rate records may be able to distinguish tectonic versus climatically caused orogenic wedge evolution. Here we present a joint sediment accumulation rate (SAR) and provenance analysis based on zircon U-Pb ages and heavy mineral composition of a drill core from the foreland of the Qilian Shan (i.e., Hexi Corridor Basin, NE Tibetan Plateau) with the aim to reveal the evolution of the Qilian orogenic wedge and its relationship to tectonics and climate. The provenance data show a gradual increase in sediment attributable to the Yumu Shan in the toe of the orogenic wedge and associated decrease in contribution from the high-elevation hinterland Zoulang Nan Shan source between 7 Ma and 3 Ma, followed by a reverse of these trends from 3 Ma to the modern. The increased contribution from the toe of the orogenic wedge (Yumu Shan) is accompanied by an increase in SAR, and we interpret this joint signal as the result of in-sequence thrusting, which caused flexural subsidence and created more deposition space in the bounding foreland. The increased contribution from the hinterland from 3.0 Ma to 1.8 Ma, accompanied with the decreased SAR, is attributed to the onset of Northern Hemisphere glaciation, which increased glacial erosion of the high-elevation hinterland areas and caused erosional unloading of the orogenic wedge, leading to flexural uplift in the foreland and reduced SAR. After 1.8 Ma, continued increase in the contribution from the hinterland accompanied with the SAR increase is less straightforward to interpret. We suspect that glacial erosion might have activated fault movements in the hinterland area, and tectonic-caused rock uplift was faster than glacial erosion. Therefore, high sediment flux from the hinterland was maintained but flexural subsidence accelerated. Our results demonstrate that both tectonics and climate have shaped regional landscape evolution and emphasize the role of glacial erosion in accounting for orogenic wedge evolution at ca. 3 Ma.