Abstract
The evolution and reforming history of the Cenozoic basins in the northeastern Tibetan Plateau(NETP)are significant for understanding the northeastward growth of the Tibetan Plateau.The sediments in these basins archived the spatial-temporal patterns of the surface uplift and deformation processes in response to remote effects of growth of the NETP.Here,we present an integrated provenance analysis of the Ningnan basin in the NETP to provide direct insights into the basin evolution and further constraints of the Tibetan Plateau's northeastward growth.In this study,the Cenozoic strata(Sikouzi,Qingshuiying,Zhang'enpu and Ganhegou formations)in the Ningnan basin yield complex detrital zircon age distributions featured by predominant age populations at 200-360 Ma and 360-540 Ma with minor Precambrian ages.Detrital zircon U-Pb ages indicate that the southwestern Ordos Block,the western Qinling orogenic belt,and the eastern Qilian orogenic belt are primary source areas.Additionally,adjacent local paleo-uplifts(e.g.,Xihua,Nanhua,Xiangshan,Liupan Mts.)also provided minor volumes of sediment.In addition,conglomerates and paleocurrent directions of the Sikouzi-Ganhegou formations exhibit an apparent change since the late Miocene,revealing an obvious provenance shift.The quantitatively determined mixing proportions of the surrounding source areas also reveals that the early source-to-sink system was replaced during the deposition of the Ganhegou Formation.Combined with previous studies,we suggest that the formation of the Ningnan basin was controlled by normal faults in extension setting and experienced continued sediment accumulation during the Qingshuiying-Zhang'enpu period;since the late Miocene,the significant provenance shift reflects the obvious northeastward growth of the NETP and led to the extinction of the Ningnan basin.
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