青藏高原东北缘隆德观音店剖面碎屑锆石年龄序列及地质意义

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

青藏高原东北缘古近纪—新近纪地层的精确时代和高原隆升扩展何时影响到东北缘地区一直是地质学家争论的焦点。此次以青藏高原东北缘隆德观音店剖面为研究对象,采用碎屑锆石U-Pb测年方法,结合区域古生物化石鉴定、古地磁测年结果,针对上述两个问题提出了新的认识。测试分析发现,青藏高原东北缘古近系清水营组上部碎屑锆石年龄序列中最年轻的峰值为17.8 Ma,研究得出如下两个认识:清水营组的沉积时代应归属于晚渐新世—早中新世,区域上具有穿时性;青藏高原隆升向东北方向的扩展推挤作用在早中新世时期就开始影响到了海原-六盘山断裂带以西地区,区域上构造-沉积-气候之间具有协同演化的耦合关系。这一研究成果为青藏高原隆升向东推挤扩展影响到东北缘地区的起始时限提供了新的时间标尺。

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.