| The Northeast margin of Qinghai-Tibetan plateau is consists of a series of mountain chains such as Qilian mountain,west Qinling,Xiangshan, Liupanshan and lots of basins such as Lanzhou,Linxia,Xining,Guide,Tianshui basin.In this paper we choise the tianshui basin to study the uplift of the Qinghai-Tibetan plateau.Tianshui basin was surround by three mountain chains which are qilian,west of qinling,liupanshan.In a more large scale it is the jont part of the huabei plate,Yangtze plate and qiangtang geological mass. The north of the tianshui basin is part of the Ordus and alashan mass,south of the basin is Yangtze palte and southwest is qiangtang mass.Tianshui baisin is also part of the Longzhong basin,Some main fault that across the north margin of west qinling control the basis structure of the basin.According to the rock property,rock granularity,sedimentary structure and texture,we have analysised the profile of the Ganquan,and demarcate the sedimentary face into 3 category,they are fluvial deposit system,alluvial fan deposit system and lacustrin deposit syetem.They present three main steps that Qinghai-Tibetan plateau was deformed by the process of India-Eurasia collision happened during 35-30Ma,15-10Ma,8-6Ma.In orde to fully understand the structure of the basin we have checked 22 profiles across the basin,From the south to north of the basin,the stratm is thinning,it is accordance to the model of forland basin.And the sediments record the uplift of the mountain adjacent the basin,According to the mountain -basin coupling hypothesis,it is the best way to reconstruct the uplift of the Tibetan plateau.This paper presents geochemistry data of neogene clastic sedimentary rocks in Tianhui basin, systematic research leads to the following conclusion:(1)MgO,CaO,Nb,Sr,Th are rich and SiO2,Al2O3,Ba,Cr,Ni,Rb are deplete in the samples,the ratio Al2O3/TiO2,Cr/Zr,Cr/Th,Th/Sc in samples are also very high.These characters indicate that granitic diorite generated in all epoch located at south of Tianshui basin(west margin of Qinling mountain)control the geochemical composition of main provenance of the neogene sedimentary rocks,and another minor parent rock is basic-super basic ignenous rock generated as the ancient Qinling paleoocean closed.The ratio K2O have been increasing in Tianshui Xiashan mud stone as time goby is another apparent character,we deem it result from the river that discharge into the basin exhumation K-rich magma rock gradually.(2)Low CIA and high ICV value indicate that weak chemical weathering in sourc region and low maturity of sedimentary rocks, then,with other evidence we can infer that the deposit rate is also low and Lack of sedimentary recycled product.(3)The thickness of strata become more and more thin from the south to north of the basin,and the sedimentary faces is also change from deep lake faces into lacustrine plain,combine with geochemistry tectonogram,we can infer Tianshui Xiashan mud stone are deposited in foreland tectonic setting.The geochemical signature of sedimentary rocks is mainly controlled by the parent petrology which generate in different tectonic setting.The early authors erect lots of element tectonic setting discrimination diagrams to infer the past tectonic activity of surrounding mountains under which sediments formed.Those diagrams have been widely used for twenty years.Studies have been carried to test the reliability of those diagrams.In this paper,we surveyed 173 samples from the same sedimentary basin,but in the twelve plot(Al2O3/SiO2,TiO2,K2O/Na2O,Al2O3/(CaO+Na2O)--(Fe2O3+MgO)diagram,K2O/Na2O--SiO2,SiO2/Al2O3--K2O/Na2O,Ti/Zr—La/Sc and Th-Co-Zr/10,La-Th,La/Y-Sc/Cr,Th-Sc-Zr/10,La-Th-Sc diagram)173 samples from the same sedimentary basin fell in different tectonic field.They do not work properly.So we can infer that it is the complex he nature of the source rocks,intensity and duration of weathering,sedimentary recycling,diagenesis,sorting and mixing cause the disagreement.We therefore recommend that these diagrams be used with prudence.
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