Provenance of the Niubao Formation and Its Geological Implications in the North Depression of the Nima Basin in the Tibet

Mi Wentian; Zhu Lidong; Yang Wenguang; Yang Lin; Huang Hui

doi:10.3799/dqkx.2017.018

Abstract：The Nima basin in the Bangong suture zone documented the geological information of the evolution of Tibetan Plateau,which helps to restore the tecto-paleogeography and provide the sedimentological evidences of uplift of the Plateau.However,the study of the NiuBao Formation of Paleogene strata in the north depression of the basin is still relatively weak.The provenance and tectonic evolution of Niubao Formation were analyzed by the methods of petrology,zircon U-Pb chronology and heavy minerals in this study.It is found that the north of Nima basin evolved into a depression controlled by collision and extrusion accompanied by the shortening of the crust and the activation of tectonic movements from Early Cretaceous to Paleogene,the north of Nima basin evolved into an depocenter controlled by tectonism.The Niubao Formation in the north depression is a bidirectional source.The source of north sediments primarily originated from the granites and acid magmatic rocks dominated by Early Cretaceous granitic rocks,while the source of south sediments were primarily sedimentary rocks,and basic or ultrabasic rocks.The detrital zircons of U-Pb ages have 5 peaks,namely 105-134 Ma,500-550 Ma,700-900 Ma,1 700-2 100 Ma and near 2 500 Ma,and 105-134 Ma is believed to be responses to the subduction of the Bangong-Nujiang oceanic crust and volcanic activity in surrounding terrances.It is further confirmed that the Niubao Formation is derived from the north and south terranes of the northern depression Palaeogeographic characteristics are determined by the extrusion and thrusting deformatior.Sedimentary processes and sources are closely related to the uplift,erosion and magmatic activities in the Nima basin.