Late Quaternary deformation rates in the Pamir-Tian Shan collision zone, NW China

Abstract:

Deformation of the Pamir and Tian Shan orogens initiated during the Neogene as a result of the Indo-Eurasian colision. The arid landscape in the western Tarim Basin, NW China, preserves suites of fluvial terraces crossing many of the Late Neogene active structures, creating fault and fold scarps. We present new deformation rates on five faults and folds, which in combination with previous studies, highlight the spatial and temporal patterns of deformation during the Late Quaternary. Suites of terraces spanning ~130 ka to ~8 ka document the basinward propagation of deformation, with the fastest rates currently located on actively deforming structures at the interface of the Pamir-Tian Shan orogens. During the last ~6 ka, the Pamir deformation front has stepped north, creating the Mingyaole South Thrust, which produced the 1985 M7.4 Wuqia Earthquake. Trenching on several sections of this fault reveal an earthquake reoccurence interval of ~1.0 ky. The Late Quaternary deformation rates on faults and folds along the Pamir-Tian Shan collision zone indicate that the locus of deformation was not concentrated on a single structure, but rather was concurrently distributed across a zone of structures. Despite numerous structures accommodating the shortening and the locus of deformation shifting throughout the Late Quaternary, the total shortening across the Pamir-Tian Shan collision zone since ~0.35 Ma has remained steady and is approximately equal to the current geodetic rate of 6-9 mm/a, as well as broadly similar to preliminary InSAR-derived deformation rates across the region.