榆木山地区玉门砾岩磁性地层及其对青藏高原东北部变形隆升意义

青藏高原新生代变形隆升过程是青藏高原新生代构造演化研究的热点问题,地处于高原东北部祁连山东北缘的榆木山是研究高原变形隆升时空过程的关键研究区之一。榆木山地区发育了一套粗砾相磨拉石——玉门砾岩,磁性地层研究表明其底部地质年代约为3.58Ma。经古水流、磁化率、野外考察等推断玉门砾岩可能主要为构造隆升的产物,同时在榆木山地区还发育3个与玉门砾岩有关的不整合面,其跨越年龄分别约为:5.23～3.58Ma、2.88～2.58Ma和<1.77～0.8Ma。综合分析认为该地区变形隆升不晚于3.58Ma,之后至少经历两期构造变形隆升,该结果比北东向分步生长变形隆升模式推测的变形隆升时间明显早约1Ma,应该是对高原东北部青藏-昆黄运动的响应结果。

Magneteostratigraphy of Yumen Conglomerate in the Yumushan Region and Its Implication for Deformation and Uplift of the NE Tibetan Plateau

The study of Cenozoic deformation and uplift of the Tibetan Plateau is a hot issue of recent earth science. The Yumu Shan, located in the northeastern margin of the Qilian Shan, Northeast Tibetan Plateau, is the key point for deciphering the spatio-temporal evolution of the entire plateau. The thickness molasse (Yumen Conglomerate) deposited in the Yumu Shan region, with bottom age of ~3.58 Ma by the magneteostratigraphy. Basing on the paleocurrents, magnetic susceptibility, field research and published results, the Yumen Conglomerate should be dominated by tectonics since ~3.58 Ma than climate change. Three unconformities related to the Yumen Conglomerate span the intervals during ~5.23~3.58, ~2.88~2.58 and <~1.77~0.8Ma, respectively. So the deformation and uplift of the Yumu Shan is not later than 3.58 Ma, then successive tectonics occurred at lest two episodic uplift. This result did not support the northward growth model of the Tibetan Plateau, and this tectonic event should be the part response of Qingzang-Kunhuang Movement.