阿齐山--雅满苏地区中-新生代构造隆升裂变径迹证据：兼论构造活动对核废选址场的意义

摘要

Tectonic activity is a fundamental discriminant factor in site assessment for radioactive waste. The tectonic activity of geological repository of radioactive waste which is located at Aqishan-Yamasu in the East Tianshan was evaluated through model studying the uplift and exhumation history by the apatite fission track dating. The result shows that apatite fission track pool-age data range from 81.7 to 51.4 Ma which recorded a cooling event of the East Tianshan during the Late Cretaceous to Eocene, which is consistent with a tectonic uplift and denudation event in the Late Cretaceous in the Tianshan. The mean track lengths range from 13.60±0.11 to 14.36±0.10 μm with the standard deviations of 0.98 ~1.22 μm, which suggests that most tracks didn’ t experience thermal annealing process after they were formed. Based on evaluated geothermal gradient, the mean exhumation rate in the East Tianshan during the Late Cretaceous to Eocene was calculated to reach 270~580 m/Ma. The geological data and further temperature-time modeling of apatite was conducted, indicating that an exhumation event existed from the Late Cretaceous to Eocene (84~49 Ma); after 50 Ma, the crust of the east Tianshan has been in a steady state, and the Cenozoic tectonic activity in Aqishan-Yamansu area has become significantly weaker than other area of Tianshan. The study shows that the geomorphologic features of present Tianshan inherit that from the Late Cretaceous, and weak tectonic activity conforms to the tectonic requirements of geological disposal of radioactive waste.%构造活动性是核废处置场评价的一项基本判别要素。文中通过对东天山阿齐山-雅满苏地区磷灰石裂变径迹测年及构造隆升剥蚀过程的模拟来评价核废处置场的构造活动性。结果表明阿齐山-雅满苏地区样品磷灰石裂变径迹年龄集中分布在81.7~51.4 Ma之间，反映出东天山地区晚白垩世-始新世存在一次明显的构造冷却事件，这与天山地区晚白垩世的抬升剥露事件相一致。磷灰石裂变径迹长度介于13.60±0.11~14.36±0.10μm之间，其长度标准差为0.98~1.22μm，显示该区磷灰石径迹形成后没有发生过明显的退火作用。根据地温梯度计算得到晚白垩世-始新世东天山阿齐山-雅满苏地区隆升剥蚀速率为270~580 m/Ma。现有地质资料及热史模拟结果表明，东天山阿齐山-雅满苏地区在晚白垩世-始新世（84~49 Ma）期间经历了强烈的构造隆升-剥露事件，自始新世以后50 Ma以来，地壳处于稳定状态，新生代构造活动不明显，其活动强度明显有别于天山其他地段。东天山阿齐山-雅满苏地区现在的构造地貌基本继承了晚白垩世的特征，处于构造活动平稳期，符合核废处置场选址的构造要求。