西藏冈底斯带南木林地区构造活动的磷灰石裂变径迹分析

Apatite fission track studies on the tectonics in Nanmulin area of Gangdese terrane,Tibet plateau.

南木林地区属于冈底斯地块的南带,研究样品取自不同时代的火山岩地层,本文报道应用磷灰石裂变径迹热年代学研究构造活动的新成果。总计获得5个样品的磷灰石裂变径迹分析结果,其中3个样品属于同组年龄,分剐为5.9±0.7Ma,5.2±0.6 Ma和8.7±1.0Ma,平均径迹长度为13.0→13.2±2.2μm,并呈单峰分布,表明它们是最近一次构造热事件的体现。另2个样品属于混合年龄,系由7.1Ma、30Ma、9.6Ma、51Ma和100Ma等5组年龄组成。所有这些年龄值,先后与区内碰撞前、同碰撞、碰撞后和陆内快速隆升作用有关。自印度-亚洲大陆强烈碰撞以来,总体上具有2阶段热演化历史,其中6～0Ma期间冷却速率为11.3℃～16.7℃/Ma,隆升速率为0.85～0.99mm/a,总计隆升幅度达5100～5940m,是本区冷却隆升的主要时期。

Nanmulin district is, located at the south of Gangdese tarrane and the research samples were collected from volcanic stratata in Cenozoic. This work reports the new achievement in tectonics from apatite fission track studies. The apatite fission track results of total 5 samples have been obtained. Three samples of the results exhibit that the individual grain ages belong to a single population with a single mean age and have central ages of 5.9 +/- 0.7Ma, 5. 2 +/- 0. 6Ma and 8. 7 +/- 1.0Ma. Their mean track lengths are 13. 0 - 13. 2 +/- 2. 2 mu m with a single peak. These characterize the recent thermal event. The other two samples give spread individual grain ages and incluse 4. 9Ma and 29Ma, and 8.0Ma, 50Ma and 87Ma respectively. These group of ages resulted from pre-collision, syn-collision, post-collision and intracontinental rapid uplift separately. As a whole, there are two stages of goelogical thermal histories since the northwordly collision of the India into Asia. It is shown that main cooling-uplifting events occurred during 6 -0Ma and caused a cooling rate 11.3 degrees C - 16. 7 degrees C/Ma, an uplifting rate of 0. 85 - 0. 99mm/a and total uplifting scale of about 5100 - 5940m in this period.