Initial rupture and displacement on the Altyn Tagh fault, northern Tibetan Plateau: Constraints based on residual Mesozoic to Cenozoic strata in the western Qaidam Basin

Abstract

The Altyn Tagh fault, located in the northern Tibetan Plateau, is a large left-lateral strike-slip fault heavily responsible for the growth and formation of the plateau during Cenozoic time. Despite its significance, the initial timing and kinematic patterns of movement along the Altyn Tagh fault remain highly debated. Here, we present a detailed analysis of the stratigraphy and geochronology of three key lithologic sections (Tula, Anxi, and Caishiling) along the Altyn Tagh fault to better understand this kinematic history. By correlating stratigraphic contacts and lithology with the U-Pb age spectra of Mesozoic samples within the western Qaidam Basin, we find the Altyn Tagh fault has experienced a total of ∼360 km of displacement during the Cenozoic. By combining seismic profile data with geologic observations, we divide the activity along this fault into two distinct stages of motion: (1) an initial stage, which occurred between early Eocene (ca. 49 Ma) and mid-Miocene time (ca. 15 Ma) and resulted in ∼170 km of offset, and (2) an early stage, which began in the late Miocene Epoch and continues into the present, resulting in ∼190 km of offset along the fault. We identify the Tula and Anxi sections as piercing points along the western segment of the Altyn Tagh fault and define these regions as residual parts of the original Qaidam Basin. These estimates suggest that motion along the Altyn Tagh fault has accelerated from an average left-lateral strike-slip rate of ∼5.0 mm/yr during initial stage faulting to a rate of ∼12.6 mm/yr between the late Miocene Epoch and present day.