Provenance analysis of the Yumen Basin and northern Qilian Shan: Implications for the pre-collisional paleogeography in the NE Tibetan plateau and eastern termination of Altyn Tagh fault

Abstract

Understanding the pre-collisional paleogeography in the NE Tibetan plateau provides insights into the growth mechanisms of the northern portion of the plateau in the Cenozoic. We conducted sandstone petrography analysis and determined U-Pb ages for detrital zircons from Cretaceous sandstone from the Yumen Basin and the northern Qilian Shan. Cretaceous strata in the northern Yumen Basin yield a unimodal age population at 290–240 Ma that indicates primary derivation from Bei Shan. Cretaceous strata in the westernmost Yumen Basin contain zircons of 2.6–2.2 Ga, 2.1–1.7 Ga, 1.4–0.7 Ga, 440–380 Ma and 300–230 Ma, suggesting source derivation from both the Qilian Shan and Bei Shan. Within the northern Qilian Shan, Cretaceous strata yield age populations of 2.8–2.3 Ga, 2.1–1.2 Ga, 480–380 Ma and ca. 270 Ma, indicating derivation from the Qilian Shan. Sandstone composition results show that a sample from the northern Qilian Shan contains more lithic fragments and plots in the recycled orogen field of the quartz-feldspar-lithics (QFL) diagram, while samples from Yumen Basin are more quartz-rich and plot close to the continental block field of the QFL diagram. This compositional difference corresponds to source variation, consistent with the detrital zircon record. Combined with existing sedimentology and low-temperature thermochronology datasets, we suggest the presence of Cretaceous topographic relief in the Bei Shan and Qilian Shan prior to India-Asia collision. Considering >300 km post-Cretaceous left-lateral offset along the Altyn Tagh Fault (ATF) and the consistently similar detrital zircon ages spectra of the samples from the Cretaceous to late Oligocene strata in the Yumen Basin, we infer the paleogeography in the NE Tibetan plateau has been similar from the late Cretaceous to the late Oligocene with ATF termination in the western Yumen Basin instead of having been linked to strike-slip faults in the Alxa or other regions to the east since its initiation.