秦岭造山带中地壳花岗质糜棱岩流变学特征与变形过程研究

The rock deformation of continental crust is controlled by the rheological characteristics of rocks, which is the basis for understanding the evolution and dynamics of the earth. The rheological properties, rheological structure and rheological stratification of orogenic belts play an important role in controlling the formation and evolution of orogenic belts. The crust and upper mantle structure of the Qinling orogenic belt are very different. The Qinling orogenic belt show the structure model of "overpass structure", and the middle-lower crust has more plastic rheological characteristics. Seismic reflection characteristics and geophysical characteristics in the middle crust show that it is not only the main orogenic period, but also the main rheological transition zone of the Qinling lithosphere structure adjustment, which is of great significance to bridge and adjust tectonic deformation and evolution between the upper crust and lower crust. The study of ductile shear zone is to understand the process of tectonic deformation of orogenic belt, to understand the rheological properties of lithosphere, and to reconstruct tectonic evolution and orogenic process of the middle-lower crust. This study intends to choose the north Qinling granitic mylonite zone on behalf of the middle crust, to carry out structural analysis, the deformation of P - T conditions and time of deformation, analysis of the rheological structure characteristics of the middle crust, status and process of rheology. This study will provide important geological evidence for the deep understanding of the tectonic evolution and orogenic process of the middle and lower crust in the Qinling orogenic belt.

大陆地壳的岩石变形受控于岩石流变学特征，岩石的流变学知识是理解地球演化和动力学的基础。造山带岩石圈流变属性、流变结构和流变分层对于造山带的形成和演化起到重要的控制作用。秦岭造山带地壳与上地幔结构极不均一，总体呈现“立交桥”式结构模型，其间的中下地壳具有更大塑性流变学特征。中地壳的地震反射特征和地球物理特性显示其不但是主造山期，而且也是现今秦岭岩石圈结构调整的主要流变过渡带，对于衔接和调整上下地壳构造变形和演化具有重要意义。研究韧性剪切带对于理解造山带构造变形作用过程、了解岩石圈流变性能、重建陆内中下地壳构造演化和造山作用过程，探讨大陆动力学具有至关重要的作用。本研究拟选择代表中地壳的北秦岭花岗质糜棱岩带，开展构造解析、变形P-T条件以及变形时间的研究，分析中地壳流变构造特征、状态和过程，为深入理解秦岭造山带中下地壳构造演化和造山作用过程提供重要地质证据。

造山带岩石圈流变属性、流变结构和流变分层对于造山带的形成和演化起到重要的控制作用。发育于造山带中下地壳的韧性剪切带对了解岩石圈流变性能、理解造山作用过程，探讨大陆动力学具有至关重要的作用。本次通过对北秦岭花岗质糜棱岩带详细的几何学、运动学、变形P-T条件以及变形时间的研究，我们为深入理解秦岭造山带中下地壳构造演化和造山过程提供了重要地质证据。我们在北秦岭中段识别出太平峪、沙沟和太白三条花岗质糜棱岩带。太平峪韧性剪切带形成于414Ma，变形温度介于650-700℃。靠近商丹带发育的沙沟糜棱岩带发育两期韧性剪切变形，早期韧性变形形成于210Ma，温度可达500-650℃，深度约18-21Km，晚期变形形成于135-144Ma，温度介于300-500℃，变形深度约10-18Km。太白韧性剪切带呈北东向斜切北秦岭，剪切带北西盘向北西伸展剪切，变形温度介于300-650℃，剪切变形形成于120Ma。北秦岭多期次的韧性剪切变形指示了秦岭造山带晚古生代以来的多期造山演化过程。