新疆阿尔泰青河-富蕴地区晚新生代隆升-剥露过程——来自磷灰石裂变径迹的证据

Late Cenozoic uplift-exhumation history of Qinghe-Fuyun region, Altay, Xinjiang——Evidence from apatite fission track

前人已经对阿尔泰造山带中-新生代的陆内造山作用进行了大量的研究工作,但对中国境内阿尔泰山的隆升过程特别是晚新生代以来的隆升研究程度较弱.阿尔泰山现今的构造面貌究竟是何时定格的,目前仍没有确切的认识.对阿尔泰青河-富蕴地区花岗岩与片麻岩5件样品进行了磷灰石裂变径迹研究,获得了该区晚新生代以来的隆升-剥露信息,并探讨了该区的热史演化过程与阿尔泰山现代地貌的形成.样品的磷灰石裂变径迹年龄为18.7±1.6-22.7±2.2Ma,封闭径迹长度分布在11.6±1.2-13.1±1.4μm之间.热史模拟表明,阿尔泰青河-富蕴地区具有四阶段演化模式：28Ma以前的稳定阶段、28-18Ma的快速冷却阶段、18-8Ma的稳定阶段、8-6Ma以来的快速冷却阶段.8-6Ma以来是本区剥露的最快时期,这一阶段的隆升造就了现代阿尔泰山的地貌,而且也存在于中国西部的其他造山带.2期主要的快速隆升-剥露事件均与青藏高原的隆升阶段有很好的对应关系,应该是对印度-欧亚板块碰撞的响应.

The Mesozoic and Cenozoic intra-continental orogenic processes of the Altay orogen have been widely studied. Howev- er, the late Cenozoic uplift and exhumation history of China＇s Altay Mountains and the problem as to when the present-day Altay Mountains were shaped remain poorly understood. Based on an apatite fission-track （AFT） analysis of five granite and gneiss samples from the Qinghe-Fuyun region and the investigation of the thermal history, the authors obtained some new information concerning the late Cenozoic uplift-exhumation of China＇s Altay Mountains. The AFT ages vary in the range 18.7± 1.6-22.7±2.2Ma, and the track length is between 11.6± 1.2 p, m and 13.1±1.4 p, m. Modeling of the fission track data shows a four-stage thermal history. The first stage is represented by a period of prolonged stability before 28Ma, the second by a Late Ohgocene-Early Miocene （28±18Ma） rapid cooling, the third by another stable period from 18 Ma to 8Ma, and the fourth by a rapid cooling after ca.8-6Ma. The last cooling phase （ca.8-6Ma） was characterized by the fast uplift-exhumation in this area, resulting in the present geomorphology of China＇s Altay Mountains. Things were similar in other orogens of western China. The two stage rapid uplift-exhumation was coeval with the uplift of the Tibetan Plateau, which should be the response to the India-Eurasia collision.