Cenozoic Uplift History Of Altyn Tagh:Evidence From The Record In Ruoqiang Depression Of The Southeastern Tarim Basin

Altyn Tagh defines the northern margin of the Tibetan Plateau,and plays an important role in understanding the uplift and northward growth of the Tibetan Plateau.Despite the significance,its Cenozoic evolution remains controversial.The Ruoqiang Depression in the SE Tarim Basin accumulated thick clastics sourced from the Altyn Tagh in the Cenozoic era,and thus bears important records concerning the Cenozoic uplift history of the Altyn Tagh.In this paper,we studied the sedimentary facies and the sedimentary rates of the Cenozoic strata as well as their contact relationship in the Ruoqiang Depression and also the Cenozoic structural deformation in Ruoqiang Depression,based on newly obtained drilling data and high-resolution seismic reflection profiles.According to these studies and combined with previous results,following conclusions can be drawn.1.Altyn Tagh was characterized by periodic uplift since 34Ma,which can be divided into three stages:sustained low-speed uplift period(34?20.4Ma),stable period(20.4-16Ma)and intensive uplift period(16?0Ma).2.The result of the investigation through field indicates that the structural deformation in front of mountains in northern margin of Altyn Tagh is very strong resulting to a series of high-angle thrust faults accompanied with related folds.These structures initiated their deformation later than the deposition of Wuqia Formation.3.The growing strata indicate that the timing of both North Altyn Fault Front and flexing depression was around 11.6Ma.The result,combined with the fact of initial uplift of Altyn Tagh during Miocene,we can conclude a northward-propagation pattern of deformation along the northern margin of the Altyn Tagh.Meanwhile,both the feature of the North Altyn Tagh Fault Front and the depocenter distribution of Wuqia Group indicate that the northern margin of Altyn Tagh experienced strong north-vergent thrusting associated with along-strike slipping.Differential uplifting was evidenced between the western and middle segment of the Altyn Tagh.4.We concluded that,together with previous studies,the sustained weak uplift of the Altyn Tagh in the first stage was caused by shear of the Altyn Tagh Fault in the middle-lower crust;while the accelerated uplift in the second stage resulted from significantly lower strike-slip on the Altyn Tagh Fault since the mid-Miocene,which induced intense crustal shortening in the northern Tibetan Plateau.5.Based on the above findings,a two-staged evolution model was proposed to explain the growth of the northern margin of the Tibetan Plateau.