The Kalpin nappe structure is a strongest thrust and fold deformation belt in front of the Tianshan Mountains since the Cenozoic time. The tectonic deformation occurred in 5―6 striking Meso-zoic-Cenozoic fold zones, and some renascent folds formed on the recent alluvial-proluvial fans in front of the folded mountains. We used the total station to measure gully terraces along the longitudinal to-pographic profile in the renascent fold zones and collected samples from terrace deposits for age de-termination. Using the obtained formation time and shortening amount of the deformed terraces, we calculated the shortening rate of 4 renascent folds to be 0.1±0.03 mm/a, 0.12±0.04 mm/a, 0.59±0.18 mm/a, and 0.26±0.08 mm/a, respectively. The formation time of the renascent folds is some later than the major tectonic uplift event of the Qinghai-Tibet Plateau 0.14 Ma ago. It may be the long-distance effect of this tectonic event on the Tianshan piedmont fold belt.
YANG XiaoPingRAN YongKangCHENG JianWuCHEN LiChunXU XiWei
On the north piedmont of Tianshan Mountains, China, the Kuytun River and Manas River transverse the Dushanzi and Manas folds, resulted in 7-level and 6-level pedestal terraces, respectively, which are the tectonomorphic marks of folding and uplift of the Dushanzi and Manas anticlines since the late Quaternary. We have collected samples from deposits of all terraces for OSL (optically stimulated luminescence) geological dating using the SMAR (single-multiple-aliquot-regeneration) method on fine grains. We have also performed dating using the 14 C method on the samples from the deposit of terrace T1 along the Kuytun River. The results show that all these deposits are of the later phase of the late Pleistocene. Comparison of terrace dating and climate change since 200 ka suggests that the terraces T1, T2, T3, T4 and T5 along the Manas River formed in 6, 8.5, 10, 14 and 32 ka, respectively. The incision time of Kuitun River's T1, T2, T3, T4, T5, T6 and T7 terraces were 1.7, 14, 20, 25, 32, 50 and 100 ka years ago, respectively. The terrace T4 along the Manas River and T2 along the Kuytun River were formed during the late part of the late Pleistocene, i.e., 14 ka. Since 14 ka, the incision of the Manas River has generated three levels of pedestal terraces, while that of the Kuytun River has only produced one level of such terraces. The latest folding and uplift of the Dushanzi anticline took place in 1.7 ka, while that of the Manas anticline occurred in 5 ka. Since 14ka or the later time of the late Pleistocene, the Dushanzi and Manas anticlines have risen by 40 and 95 m, respectively, implying uplift rates 2.7 and 6.8 mm/a for each.
