湘东南地区中、新生代山体隆升过程的热年代学研究

Meso-Cenozoic Thermochronological Analysis of the Uplift Process of Mountains in Southeast Hunan

湘东南地区位于南岭中段北缘。本文应用热年代学方法,测定了湘东南地区5个侵入体的热历史,进而分析湘东南中新生代的隆升过程,并结合区域构造背景,对热演化过程与构造发展过程之间的关系进行了探讨。研究结果表明,湘东南地区中新生代山体隆升过程总体上分为由较快速→快速→缓慢→快速的4个阶段,222~146.Ma期间以0·069mm/a的平均速率较快隆升,146.~94·11Ma期间以0·113~0·186mm/a的平均速率快速隆升,94·11~14·8Ma期间以0·014~0·028mm/a的平均速率缓慢隆升,14·8Ma^0·0Ma以0·143~0·295mm/a的平均速率快速隆升。晚近时期的隆升总体呈加速趋势。隆升过程在空间上具有非均匀性,不同岩体间隆升过程存在差异。地壳隆升过程在时间上具有明显的互补性,早期具较快速或较大幅度隆升的岩体,通常伴随着晚期相对较慢和较小幅度的隆升。根据热年代学分析结果,结合区域构造背景和其它地质资料,推断五峰仙、大义山、骑田岭等地区在中三叠世后期因构造叠置增厚了4100~7700m以上,证明印支运动早期为强烈的陆内挤压造山运动。燕山晚期岩体隆升和降温由早期构造剥蚀和晚期风化剥蚀造成,并具有良好的盆地沉积响应。湘东南地区晚近时期的快速隆升是区域性整体抬升。

Southeast Hunan lies on the margin of central Naning Mountains. Thermochronological dating was used to study the Meso-Cenozoic thermal history and the uplift processes of five plutons in southeast Hunan. Based on regional tectonic settings, the authors probed into the relationship between the thermochronological evolution and the tectonic development. The results show that the Meso-Cenozoic uplift process of southeast Hunan can be divided into 4 stages, developing in order of fairly rapid uplift→rapid uplift→slow uplift→rapid uplift, with the fairly rapid uplift process at an average rate of 0.069mm/a during 222～146.4Ma, the rapid uplift process at an average rate of 0.113～0.186mm/a during 146.4～94.11Ma, the slow uplift process at an average rate of 0.014～0.028 mm/a during 94.11～14.8Ma, and the rapid uplift process at an average rate of 0.143～0.295mm/a during 14.8Ma～0.0Ma. The uplift rate speeded up at the latest stage. The uplift processes were not uniform in space, and different plutons had somewhat different uplift processes. There existed commutative uplift reparation in time, i.e., the more rapid uplift and the larger uplift range the pluton at the early stage was, the slower uplift and the smaller uplift range the pluton at the late stage became. Based on thermochronologic analysis and regional tectonic setting as well as other geological data, the authors consider that the lower crust of Wufengxian, Dayishan and Qitianling areas was thickened by 4100～7700m as a result of tectonic stacking in late Middle Triassic, suggesting that there existed violent intracontinental orogeny at the early stage of the Indosinian movement. The Late Yanshanian uplift and the cooling of the plutons were caused by early tectonic denudation and late weathering erosion, which led to the good deposition response in basins. The latest rapid uplift in southeast Hunan was a regional integral uplift.