Provenancial Tracing for the Cenozoic Sikouzi Section in the Northeastern Margin of the Tibetan Plateau and Its Tectonic Implications

Located in the northeastern corner of the Tibetan Plateau,the Sikouzi section deposits huge thick Cenozoic strata whose provenancial analysis provides the exceptional opportunity to testify the deformational processes in the northeast Tibetan Plateau.Here,the single grain detrial zircon U-Pb ages and Hf isotopic compositions are used to trace the source variation of the 27~4 Ma strata based on the Magnetostragraphy from the Sikouzi section.Most of the U-Pb ages from 27~12Ma samples concentrate within the intervals of 200~470Ma(clustering around two peak ages of 230Ma and 440Ma),1600~1890Ma,2100~2450Ma.In contrast to the 27~12Ma samples,7Ma sample has one more detrital zircon age peak of 720~980Ma,and zircons from the sample with age of 4Ma is dominated by U-Pb ages in range of200~490Ma.In the samples collected from the Sikouzi Section,the 1600~1890Ma and 2100~2450Ma zircons mainly have positiveeHf(t)values,the 720~980 Ma zircons have positiveeHf(t)values ranging from-15.1~-1.7,and the 200~470Ma zircons haveeHf(t)values of-11.2to 12.5.Comparing these with neighboring tectonic units,we found that zircon populations at 1600~1890 Ma,2100~2450 Ma probably were drained from west margin of Ordos block,the 720~980Ma zircons have their affinity to the Xihuashan and Nanhuashan and zircons at 200~470Ma may come from west Liupanshan.The results of zircon source trace suggest that the southern Liupanshan probably initiate uplift at ~27 Ma and late Miocene deformation and uplift in this region may related to reactivation of Haiyuan-Liupansh fault system.