Research On The Uplift And Denudation Process Since The Late Cretaceous In Southeastern Xiaoxing’an Mountains

The Xiaoxing’an Mountains is located in the eastern section of the Central Asian orogenic belt between the Siberian craton and the North China craton.Since the Mesozoic,the closed orogeny of the Mongolian-Okhotsk ocean in the north and the subduction of the Pacific plate in the east have affected the tectonic evolution of northeast China.In order to deeply explore the uplift process and mechanism of the Xiaoxing’an Mountains,this paper selects the southeast section of the Xiaoxing’an Mountains as the research object,using apatite fission track,combining with the analysis of tectonic geomorphology of the southeast section of the Xiaoxing’an Mountains were studied,analysis the Xiaoxing’an Mountains uplift period of time and in space,time and intensity differences,reveal the Xiaoxing’an Mountains uplift denudation process.Using Arc GIS to analyze DEM data in the study area,the lowest elevation in the southeast section of the Xiaoxing’an Mountains is 88 m,the highest value is 1427 m,and the average elevation is 370 m.The landforms are mainly platform and hills;The minimum slope in the study area is 0°,the maximum slope is 65.08°,and the average slope is 7.59°.The best statistical unit area for undulation is 0.2025km2,There are two stages of planation planes at elevations of 600～800m and 800～1000m,respectively.The uplift and exhumation process of the southeast section of the Xiaoxing’an Mountains since the Late Cretaceous can be divided into six stages.The first stage is a uplift stage,with a cooling time of 100-69 Ma and a cooling rate of 1.07℃/Ma;The second stage is the planation stage,which lasts from 69 to 60 Ma;The third stage is the uplift stage,with a cooling time of 60-55 Ma and a cooling rate of 1.4℃/Ma;The fourth stage is the planation stage,which lasts from 55 to 46 Ma;The fifth stage is the sedimentation stage,with a heating time of 46 to 12 Ma and a heating rate of 0.59℃/Ma;The sixth stage is a rapid uplift stage,with a cooling time of 12 Ma up to now and a cooling rate of 6.25℃/MaMost of the current geomorphology of the study area is in the old age,and only two areas are in the transition stage from prime to old age: I)the border between Luobei County and Russia,and II)the border between Luobei County and Ibero-American District;Among them,the uplift in zone I occurred the latest,and the uplift intensity in zone II was relatively strongest.The overall uplift process of 100-69 Ma in the study area was not much different,and it was consistent throughout the region.The sedimentation process of 46-28 Ma was consistent as a whole and had the consistency of the whole region.The sedimentation process of 28～12 Ma has different sedimentation rates,and the overall deposition rate is faster in the east than in the western region.The current landform of the southeast section of the Xiaoxing’an Mountains has been formed by uplift since 12 Ma,with different uplift intensities on the plane.The uplift intensity decreases from southeast to northwest along the vertical direction of the Yilan Yitong fault zone.Among the two existing planation planes,the planation plane with an elevation of 800-1000 m was formed by about 6 Ma of uplift,and the planation plane with an elevation of 600-800 m was formed by about 3-2 Ma of uplift.The uplift of 100～69 Ma since the Late Cretaceous is related to the transition of the Yizenaqi plate from NNW to N direction and accelerated movement,from low angle subduction to high angle subduction,compressing the Northeast China region;The69～60Ma planation event is speculated to be caused by the activity of the Tanlu fault zone in the Paleogene,which resulted in the difficulty in transmitting the long-range subduction effect of the Pacific Ocean;The uplift at 60-55 Ma is related to the Pacific subduction activity that caused the Tanlu fault to enter a period of dextral left slip activity,which in turn caused the Nenjiang movement in the northeast region;The 55-46 Ma planation event is related to the asymmetric plate movement of the three major plates,which caused the creep of the asthenosphere in the eastern continent;The subsidence stage from 46 to 12 Ma may be caused by the joint action of the Pacific plate subduction and the Philippine plate;The uplift since 12 Ma is related to the sharp increase in the Pacific plate movement rate and the second stage of thrust of the Tanlu fault in the Miocene.