Detrital Zircon LA-ICP-MS Ages of Tertiary Sandstones from Western Qaidam Basin:Constraints on the Uplift of Altun Mountains

The Altun mountains is a collisional orogenic belt strongly modified by strike-slip-faults,constituting the current northern tectonic boundary of Qinghai-Tibet Plateau.Its uplift is remarkable part of the Cenozoic uplift of Qinghai-Tibet Plateau.This contribution presents LA-ICP-MS U-Pb dating results of detrital zircons,together with heavy mineral assemblages from sandstones of the Xiaganchaigou Formation(E13) and lower segment of the Xiayoushashan Formation(N12) from northwest Qaidam Basin.Our results show that there are significant Indosinian and Caledonian age populations in all samples.However,significant differences in age spectrums exist between the samples from Xiaganchaigou Formation ages and those from Xiayoushashan Formation.Indosinian peaks in the age spectrums of Xiaganchaigou samples are stronger than those of Xiaganchaigou,whereas the Caledonian peak gradually become stronger in Xiayoushashan samples.The stability coefficients of heavy mineral assemblages decrease rapidly from the Xiaganchaigou Formation to the Xiayoushashan Formation,indicating that their debris changed from a high maturity into a low maturity level and that provenance area for the Xiaganchaigou Formation is much farther than that of the Xiayoushashan Formation.All these results imply that the Altun had experienced significant uplift from early Oligocene to early Pliocene.Although the subduction-collision orogenes is of Altun orogenic belt was completed in the early Paleozoic,the currently exposed Altun mountains was primarily formed by much late tectonic movement,i.e.uplifting associated with strike-slip faulting in Cenozoic.This work also confirms the U-Pb age spectrum of detrital zircon,associated with heavy mineral assemblage analysis,is an effective tool in research of stratum provenance and basin-mountain coupling.