燕山及邻区晚白垩世以来山脉隆升历史的低温热年代学证据

本文根据以裂变径迹测年为主的低温热年代学方法，认为燕山及邻区在晚白垩世进入区域性伸展构造环境以来经历了造山带伸展裂解引发的6次强烈差异升降运动，分别发生在120～105Ma、95～85Ma、60～50Ma、38Ma左右、25～20Ma和10～5Ma，造成燕山及邻区约7～8km的剥蚀量。而在相邻两次强烈差异升降运动期之间的相对构造稳定期，则形成了燕山—太行山地5期夷平面以及周缘盆地多期沉积间断。燕山与邻区盆地之间晚中新世以来的快速差异升降运动导致燕山及邻区现今盆—山构造—地貌格局。

Low-temperature Thermochronological Analysis of the Uplift History of the Yanshan Mountain and Its Neighboring Area

The low-temperature thermochronological technique was used to study the uplift and denudation history of the Yanshan orogenic zone and its neighboring area, which has revealed distinct periods of accelerated crustal cooling since the late Mesozoic. The results show that the fission track ages range from 115 Ma to 50 Ma (zircon) and from 85 Ma to 6 Ma (apatite), with the apatite mean track lengths 11. 7 -10.1 /um. These data have recorded the rapid cooling events during approximately 120~105 Ma, 95~85 Ma, 60~50 Ma, 38 Ma, 25~20 Ma and 10~0 Ma. The uplift-cooling event during 120~105 Ma coincided with the activity of low-angle detachment normal fault in the Yanshan Mountain and its neighboring area and caused approximately 7 km of crustal exhumation. The uplift phase of 10 ~0 Ma coincided with the occurrence of the NE (NEE trending Shanxi graben system and caused approximately 2. 2 km of crustal exhumation. The denudation rates were approximately 0. 28 - 0. 06 mm/a during the rapid uplift and 0. 01 mm/a during the slow uplift. The stage of slow uplift corresponded with the development of five episodes of planation surfaces of the Yanshan Mountain and its neighboring area and five regional sedimentary interruptions of the Cenozoic basin in North China. On the basis of the isostasy theory, the mean altitude in the late Cretaceous was 1000 m higher than the present elevation in the Yanshan Mountain.