Geomorphic Dating of Across-Fault Gully Incision Reveals Time-Invariant Late Quaternary Slip-Rates at the Eastern Termination of the Altyn Tagh Fault

Abstract

Interpretation of fault slip-rates inferred from tectonically offset fluvial landforms is often limited by uncertainties associated with difficulties to explicitly date fluvial incision across the fault. Here, we employed morphology-based modeling to ameliorate this universal dating limitation for gullies that were differentially offset in a sinistral sense across the Altyn Tagh Fault near its eastern termination at ∼97°E. Using a stream-power erosion model with locally calibrated coefficients we calculated across-fault gully incision ages that decrease with offset magnitude, are up to threefold younger than the age of the terrace they incised and all-together point toward time-invariant slip. Luminescence dating of offset alluvial terraces at the same site suggests constant sinistral slip at 0.5 ± 0.1 mm/yr since 52 ± 4 ka. Our results suggest that the most juvenile phase of northeastward Pleistocene expansion of the Tibetan Plateau into previously stable parts of central Asia is marked by constant late Quaternary deformation rates.