利用热运动学方法恢复构造隆升过程的探索

Reconstruction of tectonic uplift process with thermo-kinematic method

构造隆升过程研究对矿产资源勘查及评价具有重要意义,是地质学家长期探索的关键科学问题之一.现有构造隆升过程的研究方法均具有一定的适用性和局限性,正反演方法之间难以建立定量关系.本文利用热运动学方法,通过离散元数值模拟,提取变形过程中离散单元的运动路径作为热年代学样品热史恢复的地质约束,实现了构造变形模拟和热年代学分析的定量耦合,在构造隆升研究中展现出巨大潜力.本文以川东地区多层滑脱褶皱作用作为研究对象,重点恢复了方斗山-齐岳山背斜在距今170~70 Ma内的隆升变形过程.热运动学分析表明:先存的齐岳山断裂串联了深部拆离面和浅部滑脱层,湘鄂西褶皱带在170~110 Ma开始形成;140~110 Ma间齐岳山断层由断展褶皱作用向断弯褶皱作用转化,齐岳山背斜开始发育,略早于东部的利川复向斜;约110~90 Ma,方斗山背斜发育,隔挡式褶皱带开始形成;约90~70Ma,隔挡式褶皱规模逐渐增大,利川复向斜逐渐紧闭.正演模型建立、地温梯度计算、三维建模技术和应力演化分析是制约热运动学方法发展和完善的关键性因素.

As a key scientific issue for geological research,the reconstruction of tectonic uplift process is of great significance to the exploration and evaluation of mineral resources.The existing research methods have some applicability and limitations,and it is difficult to establish quantitative relationship between forward and inversion results.In this paper,we applied the thermal-kinematic method,which uses discrete element numerical simulation to record the motion paths of discrete elements during deformation and provides geological constraints for the thermal history reconstruction of thermochronological samples.This method achieved the quantitative coupling between tectonic deformation simulation and thermochronological analysis,and showed great potential in the research of tectonic uplift process.We focused on the multilayer detachment folding in the eastern Sichuan basin and reconstructed the uplift and deformation process of the Fangdoushan-Qiyueshan anticline within 170~70 Ma.The thermal-kinematic analysis showed that the pre-existing Qiyueshan fault connects the deep detachment surface and the shallow detachment layer.The western Hunan-Hubei fold belt germinated at 170~110 Ma.During 140~110 Ma,the fault-propagation folding gradually transformed into fault-bend folding.The Qiyueshan anticline began to develop,slightly earlier than the Lichuan synclinorium.From 110 Ma to 90 Ma,the Fangdoushan anticline developed and the ejective fold belt appeared.During 90~70 Ma,the scale of ejective folds gradually increased and the Lichuan synclinorium became tighter.The forward modeling establishment,geothermal gradient calculation,3 D modeling technology and stress evolution analysis are the key factors that restrict the development and improvement of the thermal-kinematic method.