Tectonic Significance Of Sedimentary Record In Northern Edge Of Altyn Tagh Range

The uplift of Tibet is a major tectonic-environmental event in Eurasia in Cenozoic. It does not only record the history of continental collision and lithospheric deformation, but also strongly affected the presently geologic and topographical features of Asia as well as global climatic change. Now, it is one of the most controversial issues that concerns the uplift rate and mechanism, deformation pattern and stage of the world's highest plateau. The left-slip Altyn Tagh fault system is a major tectonic element in the Cenozoic Indo-Asian collision zone. It defines the northern edge of the Tibetan plateau and cuts the northern Tibet Plateau into different tectonic units. Altyn Tagh fault system also controls the development of basin-mountain pattern and structural framework of the northern Tibet Plateau as well as the formation and evolution of the basin on both sides. The left-slip Altyn Tagh fault has been regarded as one of the most significant faults which adjusts plateau deformation and eastward extrusion of Plateau materials. This fault is key to answer the questions on the uplift of the Tibet Plateau and its dynamics.We conducted integrated research on late Cenozoic stratigraphic sections of Milan and Ruoqiang in Xinjiang Province, which are on the northern edge of the Altyn Tagh range,, so as to interpret the deformation and uplift history of Altyn Tagh zone since Pliocene. Fission-track dating of detrital apatites, magnetostratigraphic analysis and measurements of compositions of sandstone samples were done to establish chronostratigraphic and sedimentologic evidence. Also, coarse clastic sedimentary rock samples were used to determine the unroofing history of the source region and mountain uplifting.By analyses of the compositions of sandstone and provenances, lithofacies, paleocurrent count, magnetostratigraphic features and fission-track dating of detrital apatites, we finally established the magnetostratigraphy sequence of Milan estuary stratigraphic section, combined with exiting data of this section in Late Cenozoic. The four units from the bottom to the top are: Wuqia group(>5.22Ma),Ashitu formation (5.22～3.54Ma), Xiyu formation (3.54～1.20Ma) and Wusu group (1.20～0.76Ma), individually. Also, we proposed that there have been five stages of tectonic uplifts (>5.22Ma,～3.6Ma,～2.6Ma,～1.2Ma, and <0.76Ma) and three major tectonic and sedimentary evolution periods (>5.22Ma, 5.22～3.6Ma, and <3.6Ma) from late Miocene to present in Altyn Tagh region. And this place first began to uplift slowly before 5.22Ma, followed by intense uplifting between 5.22 and 3.6 Ma, after which it experienced extremely rapid uplifting over a period of 3.6 Ma to present. Thus, the uplifting of Tibet Plateau is characterized by different pulses and inconsistence over time.