西昆仑卡日巴生岩体和苦子干岩体的隆升——来自磷灰石裂变径迹分析的证据

Uplift of the Karibasheng and Kuzigan Granite in the West Kunlun Mountains——Evidence front Apatite Fission Track Analysis

笔者对采自青藏高原西北部塔什库尔干县城西侧卡日巴生花岗岩体和苦子干碱性花岗岩体的7个不同高程的样品进行了磷灰石裂变径迹年龄和径迹长度的测试分析。结果表明,自5Ma以来,这一地区经历了脉动式的,总体由缓慢到快速的隆升过程。通过“径迹年龄—高程”法等计算的隆升速率表明,5～2Ma隆升速率为0.1mm/a±;2Ma后,隆升速率增至2mm/a±。同时对样品进行了径迹长度的分析,表明5Ma以来的隆升并不是一个持续抬升过程,存在着相对稳定的阶段,总体表现为一脉动式隆升。并结合区域地质资料分析,认为早期的隆升与印度板块与欧亚大陆的碰撞挤压有关,2Ma后的隆升是由青藏高原内部热均衡调整造成的。所测试的样品中,6个样品的磷灰石裂变径迹年龄在2.14～5.19Ma,显示出随着样品高程的增加,裂变径迹年龄增大的规律。而其中一个样品的单颗粒径迹年龄较为分散,揭示了早期与隆升有关的热历史的信息。

Apatite fission track ages and track lengths for 7 samples from the Karibasheng and Kuzigan granite in the west Kunlun Mountains are reported in this paper. The results suggest that this area undergo pulsatory uplift since 5 Ma B P. The uplift rate was about 0. 1 mm/a during 5'-2 Ma B P, and increased to 2~3 mm/a after 2 Ma B P. 6 samples'fission track ages increase with the sample's elevations. The single grain age of one sample shows a wide range; it furnishes the information of early cooling history related to the uplift. Track length analysis shows that all the samples were in the partial annealing zone during the uplift. From a geological point of view, it is inferred that before 5 Ma, the uplift was related to the collision between the Indian plate and the Euroasian continent and after 2 Ma the uplift was due to the thermal isostatic adjustment of the Qinghai-Tibet plateau.