【作者】 郑德文； 张培震； 万景林； 袁道阳； 李大明；

【Author】 Zheng Dewen Zhang Peizhen Wan Jinlin Yuan Daoyang Li Daming State Key Laboratory of Earthquake Dynamics, Institute of Geology,China Seismological Administration, Beijing 100029

【机构】 中国地震局地质研究所地震动力学国家重点实验室；

【摘要】 <正>青藏高原东北缘是高原最晚隆升的部分,这一地区隆升的时间对于大陆动力学研究以及地壳与大气圈相互作用的研究都具有重要意义。但是这一问题目前仍然存在争议。李吉均和方小敏等把前陆盆地中的砾岩作为高原开始隆升或强烈隆升的标志,认为高原开始强烈隆升的时间为约4-3MaB．P．。而Zhang et al．则认为这些砾岩是由于全球气候变化引起,高原隆升的时间应早于或晚于这一时间。争论的焦点是砾岩可否作为高原开始隆升或开始强烈隆升的标志。因此,探讨隆升与砾岩的关系对于研究青藏高原东北缘隆升具有重要的意义。沿积石山的花岗岩或花岗闪长岩采集了5个样品,裂变径迹热年代学表明积石山地区于8Ma B．P．发生快速冷却。同时临夏盆地碎屑颗粒裂变径迹结果和生长地层结果同样表明积石山地区开始构造活动的时间为8Ma B．P．。这一年龄数据明显早于积石砾岩出现的时间(约3．6MaB．P．)。根据岩体隆升与地面隆升之间的差别,提出一种新的模型,以解释隆升、气候和砾岩之间的关系。积石山岩体于8Ma B．P．开始隆升, 隆升初期,尽管岩体隆升1500m-2000m,但是由于积石山上覆的新生代地层易于剥蚀,在花岗岩基底被剥露到地表之前,地表只有少量隆升或没有隆升。随着沉积地层被剥蚀殆尽,基岩暴露于地表,地面隆升速率加快。约3．6Ma B．P．,积石山隆升到200-900m,造成了地形雨和发源于积石山的横向河流的出现,这些横向河流把积石山的花岗岩搬运到盆地中沉积下来,形成积石砾岩。如果本文提出的模型正确,那么积石砾岩不能作为青藏高原开始隆升或强烈隆升的证据。更多还原

【Abstract】 The timing and mechanisms of growth of the Tibetan Plateau are among key issues of continental tectonics. They still remain debate because of the complex relationship between rock uplift and surface uplift in a contractional setting. The complex relationship depends on the competition between rock uplift rate and erosional exhumation rate which was controlled by tectonic and climatic factors, as well as variation in rock properties. In this paper, we will illustrate the relationship by study on the Jishishan area. Apatite fission track data sampled from Jishishan suggest that rapid cooling occurred at about 8Ma B.P. This is consistent with the onset time of deformation suggested by both the detrital apatite fission track data and growth strata data in Linxia basin, but earlier than the onset time of Jishi conglomerate deposition (3.6MaB.P.). The surface uplift is the difference between rock uplift and Erosion. The surface uplift result from the competition of rock uplift and erosion, i.e., when rock uplift rate higher than erosion rate, the surface uplift, or else, there is no surface uplift. Noticing the difference and relationship between the surface uplift and rock uplift, we suggest that deformation in Jishishan area (rock uplift began) occurred at about 8MaB.P. and sustain until present. Presuming stable tectonic deformation(constant rock uplift rate) and stable climate, erosion rate change result from the change of lithology. So the development of Jishishan in late Cenozoic is as following. In the early period (8-5Ma B.P.) of deformation, the overlain Cenozoic sediment was quickly removed because it is easy eroded. Therefore, the surface hardly uplift although the rock uplift about 1500-2000m. The surface uplift rate was not enhanced until the resistant bed rock was exhumed to surface at about 5Ma B.P. At about 3.6Ma B.P., Jishishan uplifted to about 200-900m, high enough to result in the relief precipitation and traverse river originating from Jishishan. These traverse river transport the coarsed-grain to Linxia basin and lead the conglomerate deposited. Therefore the Jishi conglomerate can not be used to as proxy of onset deformation and uplift of Jishishan.更多还原