Neotectonics And Geomorphic Response In Western Yin Mountains Area,Inner Mongolia,Northern China

The research area was loaded in the west of Yin Mountains orogenic belts and the western Hetao fault depression zone in Inner Mongolia,northern China.Since late Cenozoic,the tectonic was very active,the Yin mountains uplifted continued,and the active faults development widely in the south piedmont,and also produced so many typical landforms such as river terrace,piedmont platform,alluvial-proluvial fans and basin by the Nontectonic.Thus,we can know the neotectonic types,ranges,intensity and features by researching the evolution process of those tectonic landforms.Our research not only recovered the evolution history of the regional tectonic actives,but has important implications for discussing the basin-mountain coupling mechanism in this area and the Hetao palaeo-lake and Yellow river's evolution.The neotectonics in western Yin Mountains have characteristics of succession,newbornness,intermittency,differential uplift,and controlling impact rose in the process of landforms formation.By the studying of active faults in this area,we thought that the tectonic movement is very active in Pliocene about 4.7-3.7Ma,it characterized by a series of NNE-dipping normal faults,and the relatively average uplift rate is 1.49 mm/a by our calculated.This had a further progress than forefathers'research.Through our research on southern piedmont platform of Yin mountains,we recognized that there at least experienced 2 palaeo-lake during about 109kaB.P.and59ka kaB.P;and 2 ancient river development stages;the active faults controlled the formation of piedmont platform,and the average uplift rate since 69 ka BP is 0.94mm/a approximately?calculated by the top sediment age and the height of piedmont platform?.We designated 4–5 fluvial terraces in the transverse drainage of Yin mountains,and the terraces T4 through T1 experienced four intermittent aggradation stages during the periods of approximately 76.97–58.00,51.61–46.25,41.28–32.19,and23.22–15.79 ka BP respectively,and incision stages during the periods of58.00–51.61,46.25–41.28,32.19–23.22,and 15.79 ka BP to the present,respectively.We also discussed the genetic mechanism of river terrace:they formed by the combined actions of climatic shifts and tectonic uplift,tectonic uplift controlled the depth of river downcutting,and the climate controlled the aggradation of the terraces,which was also affected by stream incision.And we analysed the crustal uplift difference by the river incision rates,the uplift of the Yin Mountains included a component of domelike tilting whereby the middle section rose more rapidly than the eastern and western section during the period of 58.00–41.28 ka BP,whereas after about 32.19 ka BP,the uplift tended to be equal on a regional scale,and the uplift rate was reduced gradually.According to the study on the morphology and sediment of the alluvial-proluvial fans,we recognized that the Yin Mountains at a continued state of uplifting from early to late Holocene,and the middle section uplift more rapidly than the eastern and western section;in addition,the climate was gradually changed from wet to dry from early to late Holocene.This paper discussed the neotectonic activity stage,characteristics and geomorphic response from Pliocene?N₂?on the basis of the above studies,laid a good foundation for further study of the basin-mountain coupling mechanism and the evolution of geography pattern in this area.