Lydia M. Staisch

The initiation of left-lateral motion along the Kunlun Shan; evidence from Dongdatan Valley

 

The goal of this project is to refine our knowledge of the spatial and temporal record of deformation events along the northern margin of the Tibetan Plateau, and understand the processes and mechanisms contributing to these deformation events. We specifically focus on constraining the initiation of sinistral faulting in the Kunlun Shan from an early Cenozoic regime of crustal shortening and thickening because a change in the stress field may relate to the attainment of high elevations in northern Tibet. During early Cenozoic shortening and thickening, gravitational potential energy increased likely increased until vertical stresses equaled or exceeded the least compressive horizontal stress (east-west), after which point deformation would, theoretically, shift to strike-slip faulting.

 

To constrain the onset of left-lateral strike-slip faulting along the Kunlun Shan, we pair structural observations, fault gouge dating, and low-temperature thermochronology. Fault gouge dating of the Dongdatan Thrust Fault indicates that crustal shortening was active along the Kunlun Shan by 47 Ma. We have new apatite (U-Th)/He, apatite fission-track, and zircon (U-Th)/He ages from the Dongdatan region which, along with published low-temperature thermochronologic data, indicates that rapid cooling occurred throughout the Kunlun Shan between ~35 - 25 Ma, and that younger thermochronologic ages are concentrated near active, large-scale, strike-slip faults. We interpret this to suggest that crustal shortening was active until the early Miocene (similar to Hoh Xil Basin) and that left-lateral shear initiated soon there after, perhaps as early as 21 Ma. We interpret this to suggest that high elevation in northern Tibet was attained by the mid Miocene, which is in general agreement with the sparse paleoelevation data currently available.