| The northeastern margin of the Tibetan Plateau is the forefront region of the plateau.It is considered to be an ideal area for studying the uplift,evolution and dynamics of the plateau,where tectonic deformation is strong since Cenozoic.The Wushan basin,located at the intersection of Liupan Shan and West Qinling,is considered as a most northeastern part of the northeastern plateau.It is a key position to study the northeastern growth of the plateau,which is filled with Cenozoic sediment successively,with an active tectonic deformation history.Up to now,there are many researches on magnetostratigraphy,paleontology and sedimentary sequence study in this area,with a breakthrough in chronostratigraphy,sedimentary evolution and paleoclimatic evolution of Wushan basin.However,the research on tectonic deformation is relatively weak,such as what's the evolution of tectonic deformation history in this region,how many stages of tectonic deformation recorded in this basin,whether it is in connection with other regions in northeastern Tibetan Plateau,when and how did its tectonic deformation history respond to the main body of the Tibetan Plateau and so on.In view of the foregoing,it will keep us from deeply understanding the timing and mechanism of the Tibetan Plateau.For the above mentioned weakness,we choose detrial fission-track thermochronology as the main research method to carry out a study on the Wushan section where sediment is complete and successive,and mammal fossils are rich,supplemented by magnetic stratigraphy,sedimentology,paleocurrent analysis and previous research results.We attempt to reveal regional tectonic deformation history recorded by sediment of Wushan basin and capture the major tectonic event sequence in West Qinling since the Cenozoic,looking forward to obtain a deep understanding of the Tibetan Plateau uplift process and providing chronological evidence for the northeast margin area.The main conclusions and cognition are as follows:(1)Through a variety of indicators to verify,such as the comparison of fission-track data and the corresponding sedimentary age,the estimate of the possible maximum burial temperature from paleo-geothermal gradient and the sedimentary thickness,the track length distribution characteristics and other indicators,we suggest that the samples in Wushan basin have not been strongly annealed after deposition and fission-track data records the signal of the geological history in provenance.(2)From the morphological analysis of each apatite grain,we find every sample consists of rounded or sub-rounded grains mostly,with obvious erosion and broken characters.It indicates that probable fast exhumation activities in provenance.In contrast,there are also several euhedral apatite grains,but they only represent some weak volcanic signal and can't play a decisive effect in the final result.(3)Based on the apatite fission-track data published in the periphery bedrock of Wushan basin,we plot the contour map of bedrock fission-track age in West Qinling area.After the comparison between the data in Wushan basin and the map,we interpret that the sediment source areas of the Wushan basin were mainly from the Western Qinling,and that it had different construct active source areas in different sedimentary evolution stages.(4)Combining with previous research results in the West Qinling,the northeast margin and the main body of Tibetan Plateau,the apatite fission-track age components in Wushan basin reveal that the Western Qinling area has experienced at least five possible tectonic events during Cenozoic.The five rapid exhumation events occurred at 61.3–48.2Ma,36.0–33.2Ma,28.8–27.4Ma,24.5–22.2Ma and 13.3–12.6Ma,respectively. |
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