从裂变径迹分析新疆阿尔泰南部地区构造活动与古地形的变化

对阿尔泰东南部地区磷灰石样品进行裂变径迹年龄分析及热历史演化模拟，分析计算岩体的隆升剥蚀速率及隆升剥蚀幅度，力求恢复古地形。裂变径迹年龄在(59.4±5.8)～(109.7±8.1) Ma之间变化，径迹长度为(12.0±2.5)～(13.7±1.5) μm。从热历史模拟结果可看出，总体上经历了三阶段的隆升-剥露热演化模式：108 Ma之前的初始整体隆升阶段；108～28 Ma的缓慢冷却阶段；28 Ma以来的快速冷却过程，冷却速率为1.25～1.61 ℃/Ma，剥蚀量为1.17～1.50 km，是本区剥露最快时期。对所有样品单颗粒年龄及混合年龄进行分析统计得到4组年龄，这种年龄不均匀分布亦是不均匀构造抬升的一种反映，主要受抬升速率差异的影响。90 Ma至今，古地形高度变化为3 895～821、2 250～762 m等，变化幅度高达3 300～1 400 m，研究区可见高山成谷，谷地抬升的现象，各阶段古地形情况显而易见。反演古地形并进行均衡校正可知，均衡回弹在阿尔泰地区造山后期的岩石抬升中起重要作用。

Apatite Fission Track Analysis on Tectonic Activities and Paleotopography in Southern Altai Region,Xinjiang, China

This work engages apatite fission track evidences on thermotectonic history, rock uplift rate, denudation extent in southeastern Altai region. Fission track ages of 14 samples range from (59.4±5.8) Ma to (109.7±8.1) Ma and the length is between (12.0±2.5) μm and (13.7±1.5) μm. Thermal modeling reveals that the samples have a three-stage of uplift-cooling history. The first stage is in an overall initial uplift before 108 Ma, the second stage from 108 Ma to 28 Ma experiences a slow cooling phase, and the last stage through a rapid-cooling process since 28 Ma with a cooling rate 1.25-1.61 ℃/Ma and denudation amount 1.17-1.50 km, the fast exhumation period in the area. The sample ages could be divided into 4 age groups, reflecting multiple tectonic events with different uplift rates. The paleotopography altitude changes from 3895 m to 821 m, 2250 m to 762 m etc., and the amplitude of changes reaches to 3300-1400 m since 90 Ma. The phenomenon of Alpine turning to valley and valley uplifting is visible in the studied area, indicating various stages of paleotopography. Based on inversion of ancient landform and equilibrium correction, the equilibrium rebound would play an important role in the rock uplift during the Altai post-orogenic period.