The Cenozoic Tectonic Uplift Sedimentary Record Of Orogenic Belt In Hoh Xil Area,the North Part Of The Tibetan Plateau

The Hoh Xil Basin in the Tibetan Plateau is the biggest Cenozoic continentalsedimentary basin which develops6000m of the Cenozoic sedimentary stratas，thebasin records two kinds of uplift imformations of orogenic belt：The northern marginof plateau orogenic belt-East Kunlun Mountain and plateau inland orogenicbelt-Tanggula Mountain，which is the key area and communicating vessel to constructthe northward expansion process of “initial Tibetan Plateau”.The uplift amplitudeand timing succession are preconditions to discuss the important scientific problemssuch as: the boundary migration of northern plateau in different period，whole upliftor stage uplift of plateau，“early uplift” or “late uplift”， the climatechanging-vegetation growing-enviromental effect in the process of plateau uplift，etc.At present，formers had accumulated a lot of advanced results in researching HohXil Basin including the basin sedimentary sequence filling and environmentalevolution，magnetic stratigraphy，the stage of magmatic activity，the quantitativeanalysis of crust shorten deformation，the formation time limit of south marginorogenic belt thrust nappe structure，the research of the cooling event uplift in northmargin orogenic belt，etc. But，through analysis from the point of sedimentary basin，it is unknown that when did the periphery orogenic belt (like east Kunlun mountain)provide material source for Hoh Xil Basin，which is the premise to discuss its uplifttiming. In addition， it is almost a blank filed that do low-temperaturethermochronology research in orogenic belt via clastic mineral in sedimentary basin，there are rarely articles and papers for this specific study.Therefore,this paper has obstain higher resolution of apatite fission track (AFT)binomial fitting cooling ages、the vertical changes sequence of paleocurrent direction.the writer has conduct a detailed study to provide fundamental data for the growprocess of the northern part of Tibetan plateau via integrate the data such as the fillingcharacteristics of basin formaition，the longitudinal sedimentary phase and clasticcomponents developing trend of the typical profile，the spread pattern of regionalpaleocurrent，etc. and then get the following recognition：1.Through the field observation of typical profile in Hoh Xil Basin and according to the characteristics of lithofacies combination，the sedimentary structure and the thinsection identificate indoor，etc. the writer has analysed the sedimentary facies of thetypical profile. The profile of QSP is only develop the lake phase sedimentary system，and then can be further divided into the lakeshore-shallow lake-playa subphasecombinations；and we can identify fluvial facies and lacustrine facies in QTP profile，and then can be further divided into the floodplain-lakeshore-shallow lake-playasubphase combinations; in Mariqu profile，which developed two sedimental systems，the fluvial facies and lacustrine facies， and which can be divided into thechannel-floodplain-lakeshore-shallow lake-playa subphase combinations.2.According to the characteristical analysis of clastic composition andpaleocurrent direct vertical evolution，and combine with the features of the regionalrock formation units and the characteristic of the regional paleocurrent spread，we canconsider that in Cuorendejia basin，the stream distribution was more concentrated inEocene，the flow directed to north. the sedimentary rock lithic are mainly to the clasticcomposition，it is shows that the source of clastic materials were came from thePaleozoic-Mesozoic mian fotmation in Qiangtang Block; until the Qligocene era(Yaxicuo group)， the paleocurrent direction was provided with the style ofbidirectional polar distribution，the mianstream was directed to north，but theappearance of the direction of mainstream turned to east or even to southeast is reflectthat the western and northern of Hoh Xil Basin were also uplift gradually，this forcedrivers’ flow turned to the east，and then emerged longitudinal river systems whichflows were turned west to east. The mian clastic compositions are the lithic of slate，the lithic of quartz schist and the lithic of siliceous，which is the chararcterized rockcombination in Triassic Bayan Har group，this is comfirmed that the Bayan Har Blockbecame geomorphology highland and provenance supply district through its partialuplift; In Miocene，the main clastic compositions of Wudaoliang group are chert rocksand siltstone， among them there are sandwiched between quartz sandstone，occasionally schist，phyllite，carbonate lithic，granite lithic，etc. it is shows that theprime attributions of provenance are Triassic Bayan Har group and east Kunlunmountain.In The Tuotuohe Basin，its property of overcompensated is significantly inEocene period， and its paleocurent direction is characteristic by unidirectional north.the clastic compositions are mainly gray-black micrite. This is shows that in thatperiod，the prime attributions of provenance should be Zaduo group of LowerCarboniferous，Jieza group of Upper Triassic and Kaixinling group of Lower Permian in Tanggula area; In Eocene-Oligocene period，the direction of mainstream was stillpoint north，in the middle of the period，the direction emerged nearly east to west，overall its north-north-west. Compared with the time in Eocene，the component ofsandstone lithic was emerged more metamorphic lithic. occasionally meso basalticeffusive rock lithic. it is shows that the direction of provenance were mainlysouthwest and south. The prime attributions of provenance are Jieza group of UpperTriassic and Kaixinling group of Lower Permian in tanggula area. The direction ofpaleocurrent in Late Oligocene-Miocene was southwest. However，the sandstonecompont appeared low-value near the boundary line between Oligocene and Miocene.The metamorphic component increased steadily upward，the lithic components showsthe affinity with the Triassic Bayan Har group in the north and northeast direction.The prime attributions of provenance is the Metamorphic belt of Triassic Bayan Hargroup.3. The periphery orogenic belt in Hoh Xil Basin shown three tectonic uplifts inoverall pattern from Cenozoic era according to the AFT mixed age binomial fittingresolved and the lag time analysis of the AFT cooling age of the youngest component.The three tectonic uplifts are:Paleocene(65-51Ma)，Late Eocene-Oligocene(38-28Ma)，Late Oligocene(28-24Ma)，and this is comfired by the data of magmatism in the basinand its surround area and the cooling events.etc.Intergrate above reseaches indicate that: the process of plateau uplift is prefer―early uplift‖and―stage expansion is from middle to north‖.In the north area ofTibetan Plateau，the Tanggula area in Qiangtang block developed thrust nappestructure(TTS) by the condition of Indian and Eurasian continental collision inPaleocene period(64-51Ma)，in the leading edge of TTS，the Hoh Xil Basin wasdeveloped，Simultaneously，Kunlun mountain-Bayan Har mountain area wasn’tuplifted significantily; With the continuing northward subduction of the Indian platein Late Eocene-Oligocene period(38-28Ma)，the Tanggula Mountain had appearedthe most significant of uplift and denudation rate，they were concentrated in38-34Ma.Over the same period，the uplift of north Bayan Har mountain and east Kunlunmountain had began，but not peaked；Until Late Oligocene(28-24Ma)，the ancestralriver systems of Hoh Xil Basin had large-scale changes，the lithic components of thewhole basin had reflected the affinity with Bayan Har mountain and east Kunlunmountain area， the formation of basin suffered a large area of extrusion， Bayan Harmountain-east Kunlun mountain had uplifted certain height. So far，the plateau hadbasically completed the initial uplift pattern. With the Bayan Har mountain and east Kunlun mountain provided provenance for Hoh Xil Basin continuously，while theregional massive unconformity events appeared in Miocene，the towering Kunlunmountain standing in the northern edge of the Tibetan Plateau.