The Sedimentary Records Of The Tectonic Uplift Of The East Kunlun In The Cenozoic

Based on the systematic studies of sedimentology, single detrital zirconchronology and apatite fission-track thermochrology of the Cenozoic stratum of theChangweitai sections before the Qimantage Mountain in the west section of the eastKunlun Montain, Combined with other research results, the structure evolution historyin the East Kunlun region is discussed. Following views have been summarized.1. The Changweitai section mainly has three sedimentary systems: lake facies,delta facies and alluvial fan facies. Lake Facies developed from the XiaganchaigouFormation to the bottom of the Shangyoushashan Formation at the bottom of thesection, and it experienced two integrated lake-flooding and lake-withdrawal process.The Shangganchaigou Formation and the Xiayoushashan Formation period witnessedthe deepest lake water period, and the most stable lake basin period, with thedevelopment of the whole set of lake and laminated limestone. The water at the top ofthe Shangyoushashan Formation gradually became shallow and turns into transitionalenvironment. The lake experienced overall withering during the Shizigou sedimentaryperiod and mainly developed a whole set of basin marginal facies alluvial fansedimentary.2. The thesis conducts a systematic analysis of the microscopically identificationfeatures and cathode luminescence feature of the main detrital component in theChangweitai section, and statistics of the vertical content of the Changweitai section.The results show that vertically the change of the debris mainly concentrates betweenthe Shangganchaigou Formation and the Xiaganchaigou Formation, theShangyoushashan Formation and the Xiayoushashan Formation. Significant changeshave been noticed in the content of the quartz gross, microcline, intrusive rock debrisand metamorphic rock debris; while tremendous changes also occur between the top and bottom of the Youshashan Formation in the content of the quartz gross, quartzwith intrusive rock sources, quartz with the metamorphic rock sources, plagioclase,debris gross, effusive rock debris and intrusive rock debris. The changes of the debriscontent may represent the coming up of the tectonic event in the source region. At thesame time, contrastive analysis of the debris content also reveals that QimantageMontain is indeed the source of the Changweitai section.3. Single detrital zircon chronology in the Changweitai section has beenconducted. Most zircons are colorless and transparent or smoky gray magmatic originzircon, with only small amount of light purple, isabelline and smoky gray magmaticorigin, and even less amount of hydrothermal solution zircon. Typomorphicpeculiarities of the zircon between each stratum also reveal significant differences,mainly in the mutation of the color, size and ratio of the length and width in theShizigou Formation and Shangyoushashan Formation. Moreover, slight changes ofthe ratio of length and width of the zircon also took place in the ShangganchaigouFormation and Xiayoushashan Formation. The features perhaps indicate the changesof the material source during the period.The isotope chronological research of the debris zircon U-Pb shows that agespectrum characteristics has similar U-Pb characteristic peak in the Cenozoic stratumof the Qaidam Basin, suggesting they have similar source area. Comparison with theisotope chronological age characteristics of peripheral orogenic belts reveals that agespectrum of the debris zircon from the Cenozoic of the Changweitai section is similarwith the East Kunlun Mountain, which indicates that the East Kunlun Mountain hasalways been the main source area of the Qaidam Basin since the XiaganchaigouFormation, and also means that the initial uplift of the Qimantage Mountain in thewest part of the East Kunlun Mountain occurs early than at least the late Eocene.However the Paleozoic debris zircon features on the vertical direction show thatsignificant changes have taken place of the source components provided by the EastKunlun Mountain for the basin, at least between Shangganchaigou and XiaganchaigouFormation stratum, and Shangyoushashan and Xiayoushashan Formation stratum.4. Apatite fission-track thermochrological research shows there are five tectonicactivities events in the East Kunlun region since Middle and Late Mesozoic: LateJurassic to Early Cretaceous (150-120Ma), Late Mesozoic (100-70Ma), EarlyCenozoic (65-40Ma), from Eocene to Early and Middle Miocene (30-15Ma), andsince Middle and Late Miocene (15-2Ma). Tectothermal events in each period havebeen identified by isotope chronology of the Kunlun areas and northern margins of the plateau and also some sporadic tectonic records.The tectonic denudation movements of Early Cenozoic in the research areas isthe most common event in the orogenic belt of east Kunlun Mountain, which canexhibit the early period of Cenozoic collision of India Plate and Eurasian Plate. Theeffect of collision can be seen in the northern part of Qinghai-Tibet Plateau. Thephenomenon of structuring in the Mesozoic epoch is in great frequency, which showsthe existence and occurrence of tectonic uplift in this epoch. In the meantime, thephenomenon might be caused by the northern thrusting of the Yarlung Zangbo Riverbasin. However, the movement during the late Jurassic period and the earlyCretaceous period is not active, which can represent the Hyperplasia collage ofBangong Lake—Nujiang ophiolite belt and Eurasian continent in the evolution ofTethys structure. The tectonic events during the Eocene and the Miocene are mainlycaused by the constant thrusting and squeezing of India Plate. Because of the thrustingand squeezing of the rigid blocks from northern part of the plateau, and the greatmovements during Eocene to Early Miocene, the east Kunlun Mountain was formedlike a sudden rising curtain.