The Age Of Upper Jinghe River Terraces At The Eastern Piedmont Of Liupanshan And Its Significance For Neotectonic Movement

The Liupanshan region is located in the transitional region between the Ordos block of the western North China Plate and the Qilianshan orogenic belt of the northeastern Qinghai-Tibet block. It is all important part which belongs to the northern section of the north-south seismic structural zone. Liupanshan is the key region to research the uplift and tectonic deformation of the northeastern Tibetan Plateau. Jinghe River terraces at the eastern piedmont of it are geomorphology carriers to record tectonic uplift process of Liupanshan since the Quaternary. Through the study made the following understanding:(1) Through the detailed study of profiles of the upper Jinghe River terraces at the eastern piedmont of Liupanshan show that Jinghe River mainly developed 5 river terraces, T5, T4 and T3 of Liushugou are accumulation terraces,T2 and T1 are pedestal terraces, terraces in Gaojiashan are both erosional terraces and pedestal terraces.(2) The age of 5 levels of terraces defined respectively 541 ka B.P.? 477 ka B.P.? 279 ka B.P.? 60 ka B.P. and 8 ka B.P. by OSL, ESR dating results and loess- paleosol sequences.(3) The morphological types of terraces and the relationship between age of terraces and climate change indicate that the upper Jinghe River terraces are mainly driven by tectonic uplift while the effects of climate change are complementary. (4) Between 541 ka B.P. and 279ka B.P., Jinghe River in Liushugou region is accumulation area and the accumulation rate is 0.31m/ka, correspondingly, the incision rate averaged 0.37 m/ka in Gaojiashan which is loacated in tectonic uplift region, the two are basically consistent, therefore, the thick gravel layer of T5, T4 and T3 is sedimentary response of the accumulation area to Liupanshan rapid uplift; In 279ka B.P., T2 and T1 are driven to form by the effect of sustained uplift in Liupanshan after Liushugou transforms to erosion areas, and the incision rate averaged 1.13 m/ka. The event is results of Liupanshan eastward extrusion uplift under the background of expansive uplift of the northeastern Tibetan Plateau. The study provides a new evidence for the cognition that the Tibetan Plateau expands in a way of area and volume.(5) By calculating tectonic differential uplifting rate(?UT) of Weihe river terraces in Longxi region and Jinghe River terraces,the results show that ?UT (max), ?UT (min) of T5 period tectonic are positive, indicating that the activity of the west Liupanshan is stronger than the east.Meanwhile ?UT (max), ?UT (min) of the T4 and T2 stage are negative, indicating that the activity of east side is stronger than the west side of Liupanshan.