The age sequence of the detrital zircons from the Guanyindian section in Longde, the northeastern margin of the Tibetan Plateau, and its geological significance

The precise age of the strata at the northeastern margin of the Tibetan Plateau in the Paleogene-Neogene, and the initial time when the uplift of the Plateau affected its northeastern margin, have always been two main bone contentions among geologists. The Guanyindian section at the northeastern margin of the Tibetan Plateau is our research subject. We gain new insights to the two mentioned issues by using detrital zircon U-Pb dating in combination with the previous results concerning regional paleontological fossil identification and paleomagnetic dating. The dating results show, among the samples from the upper Paleogene Qingshuiying formation at the northeastern margin of the Tibetan Plateau, the youngest peak is 17.8 Ma. Two conclusions are drawn from the research results. Firstly, the deposition age of the Qingshui formation is from the late Oligecene to early Miocene, showing the characteristic of diachronism. Secondly, the northeastward extension and pushing of the uplift of the Tibetan Plateau has begun affecting the west of the Haiyuan-Liupanshan fault zone since the early Miocene with a coupling relationship among tectonics, sedimentation and climate in the area. The research findings provide a new time scale for determining the initial time when the northeastward pushing of the Tibetan Plateau began to affect its northeastern margin.