喜马拉雅造山带晚新生代构造隆升的裂变径迹证据

Evidence from Fission Track Ages for the Tectonic Uplift of the Himalayan Orogen during Late Cenozoic

喜马拉雅造山带的隆升,在地质学研究中是一个非常让人感兴趣的问题,为了对其进行定量研究,揭示隆升历史及幅 度等相关问题,运用磷灰石、锆石裂变径迹法对研究区淡色花岗岩进行了分析,所取样品的裂变径迹年龄位于17.0～5.7Ma 之间,小于其地层时代或侵入年龄(40～17Ma),表明研究区喜马拉雅造山带的强烈隆升开始于晚新生代.用磷灰石裂变径 迹年龄来计算可知,研究区内花岗岩5.7Ma以来的冷却速率和剥蚀速率分别为18.421℃/Ma和0.526mm/a.5.7～ 9.2Ma间的相对抬升与剥蚀速率为0.229mm/a,9.2～17.0Ma间的相对抬升与剥蚀速率为0.032mm/a.用锆石裂变径 迹年龄来计算知,研究区内花岗岩16.2Ma以来的冷却速率和剥蚀速率分别为12.963℃/Ma和0.370mm/a,冷却速率和 剥蚀速率均小于用磷灰石计算的结果.因此说喜马拉雅造山带从9.2Ma到现在隆升和剥蚀的速率是处于加快的状态.

The uplift of the Himalayan orogen is an interesting geological problem. In order to quantitatively discuss the uplift, its history, range and correlative problems, this paper analyzes the leucogranite by dating the apatite and zircon fission track ages. The fission track ages, which range from 17.0 to 5.7 Ma, are less than the strata ages and the intruding ages, which range from 40 to 17 Ma. So the authors infer that the violent uplift of the Himalayan orogen began in the late Cenozoic. According to the fission track age results of apatite, from 5.7 Ma B. P. the cooling and denudation rates were 18.421 °C/Ma and 0.526 mm/a respectively. The relative rate of uplift and denudation during 5.7-9.2 Ma B. P., 0.229 mm/a is correspondingly faster than that during 9.2-17.0 Ma B. P., 0.032 mm/a. According to the fission track age results of zircon, the cooling rate and denudation rate from 16.2 Ma B. P., 12.963 °C/Ma and 0.370 mm/a is less than that calculated with apatite. All the results show that the quick uplift rate and denudation rate of the Himalayan occurred from 9.2 Ma B.P..