Spatiotemporal patterns of the Late Quaternary deformation across the northern Chinese Tian Shan foreland

The investigations of active deformation across a mountain foreland can provide important insights into the pattern and dynamics of deformation of an active orogenic belt. Here we focus on the spatiotemporal patterns of the Late Quaternary deformation along the north piedmont of the Chinese Tian Shan, a mountain range formed by the ongoing India-Asia collision. By using a terrace as the reference and applying the area-conservation method, the Holocene shortening rate of the Halaande anticline, a fold of the distal structure Belt III in the foreland, is estimated to 2.14 ± 0.24 mm/yr for the first time. Similarly, we re-calculate the Holocene shortening rates of the other anticlines of Belt II-III using the magnitude of shortening documented by river terraces and the terrace formation ages published previously. The summed Holocene (10³-year timescale)shortening rates of individual anticlines along N–S transects are ~2–4 mm/yr, consistent with the Late Pleistocene (10⁴-year timescale)shortening rate but about 2–6 times higher than the long-term (10⁶-year timescale)average shortening rate of ~1 mm/yr during the past several million years. Together with the shortening rates of individual anticlines at the 10³-year, 10⁴-year, and 10⁶-year scales, these observations imply that the deformation across the northern Chinese Tian Shan foreland has accelerated since at least Late Pleistocene. By summing the Late Quaternary rates of shortening in the southern Chinese Tian Shan foreland (4–5 mm/yr)and the intermontane basins in the hinterland of the Tian Shan (~2 mm/yr), the Late Quaternary rate of shortening across the Tian Shan range (between longitude 83°E and 87°E)amounts to ~9.0 ± 1.0 mm/yr, approximately matching the modern shortening rate of ~8 mm/yr derived from the GPS measurements. These results imply (i)that the deformation across the Tian Shan range and its foreland basins (between longitude 83°E and 87°E)could have not been changed significantly since at least Late Pleistocene; (ii)that, in the northern Chinese Tian Shan foreland, the recurrence interval of paleoseismic events during the past tens of thousands of years may be determined by a linear extrapolation of the Holocene or even geodetic rate of deformation.