Abstract

New apatite (U-Th)/He from the northeastern margin of the Tibetan Plateau (north Qilian Shan) indicate rapid cooling began at ∼10 Ma, which is attributed to the onset of faulting and topographic growth. Preservation of the paleo-PRZ in the hanging wall and growth strata in the footwall allow us to calculate vertical and horizontal fault slip rates averaged over the last 10 Myr of ∼0.5 mm/yr and ∼1 mm/yr respectively, which are within a factor of two consistent with Holocene slip rates and geodetic data. Low fault slip rates since the initiation of the northern Qilian Shan fault suggest that total horizontal offset did not exceed 10 km. Further, emergence of the northern Qilian Shan occurs during a period of increased aridity in northern Tibet but is associated with only a minor expansion of the northern plateau perimeter, which is well established near collision time. Outgrowth of the northern Qilian Shan at ∼10 Ma could be simple propagation of the larger Qilian Shan system, occurring in response to decreased slip rates on the Altyn Tagh fault or as a result of the change in GPE of the central plateau.

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