商丹构造带中唐藏-黄柏塬韧性剪切带的构造分析：多尺度模拟方法MOPLA的应用

Structural geology has grown from the single-scale kinematic studies to multiscale full-mechanics comprehensive studies. The successful development of the multiscale simulation approach, the Multi-Order Power-Law Approach (MOPLA), makes it possible to quantify tectonic-scale deformation boundary conditions according to small-scale structures and fabrics. The Qinling orogenic belt is the major part of the central China orogenic belt. There are abundant multiscale structures and fabrics in the orogenic belt. These structures and fabrics have recorded valuable information about the evolution of the Qinling orogenic belt. However, these structures and fabrics have not been well studied. Especially, the relation between them and the tectonic evolution of the orogenic belt is still unclear. The Shangdan tectonic zone is a major part of the Qinling orogenic belt. We propose to carry out detailed multiscale structural analysis of the Tangzang-Huangbaiyuan ductile shear zone in the Shangdan tectonic zone, in order to establish the structural geometry and deformation sequences of the shear zone. We plan to use 40Ar-39Ar age dating and zircon U-Pb geochronology to constrain the deformation time. We apply MOPLA to contain the tectonic-scale boundary conditions. The Tangzang-Huangbaiyuan ductile shear zone is located in the key area of the Shangdan tectonic zone. The successful completion of this project shall significantly contribute to understand the deformation process and mechanism of the Shangdan tectonic zone and lay the foundation for a better understanding of the tectonic evolution of the Qinling orogenic belt from late Paleozoic.

构造地质学已经从基于单尺度的运动学研究进入基于多尺度完整力学的综合研究，多尺度模拟方法（the multi-order power-law approach, MOPLA）的成功创建，为利用小尺度构造信息量化大尺度变形边界条件提供可能。秦岭造山带是中国中央造山系的重要组成部分，其中发育了丰富的多尺度变形组构，这些组构记录了造山带构造演化的珍贵信息，但它们的研究程度并不高，尤其是这些组构的形成与秦岭造山带构造演化的关系不明确。商丹构造带是秦岭造山带的重要组成部分，本项目拟选择发育于其中的唐藏-黄柏塬剪切带为靶区，通过详细的野外和室内构造解析，建立变形序列；结合同位素测年，限定变形时间；运用MOPLA模拟方法，量化变形的大构造边界条件。唐藏-黄柏塬剪切带处于商丹带的关键位置，该项目的顺利完成能够更好地理解商丹构造带的变形过程、变形规律及变形机制，为完善秦岭造山带晚古生代以来的构造演化提供支持。

本项目主要对秦岭造山带中的商丹构造带从野外、室内和多尺度模拟等三方面进行了研究，野外研究发现：元龙地区发育S>L构造岩，剪切指向标志指示右行剪切，变形时代为387–393 Ma；黄柏塬地区发育L>S构造岩，剪切指向标志时而左行时而右行，说明该地区的运动学背景以沿走向伸长，沿垂直走向和竖直方向缩短为主；剪切指向不一致说明沿走向伸长速率不一致，变形时代早于122.46±0.75 Ma，根据变形特征及秦岭造山带构造演化背景，推测变形时代为中晚三叠世；东秦岭商南丹凤地区记录近水平拉伸线理及近直立的置换面理，在近水平的面上可以在露头尺度及显微尺度观察到剪切指向标志指示左行剪切，根据前人在沙沟剪切带的工作及在商南丹凤地区的Ar-Ar年龄，我们将这期变形限定在ca. 246 Ma-201 Ma。. 用MOPLA多尺度的模拟方法，限定变形时的大构造边界条件。得到的结果是华南华北在三叠纪进行斜向汇聚，在东秦岭地区，斜向汇聚的汇聚角在40°-60°， 同时汇聚产生垂直造山带的缩短有40%被平行造山带伸长所消解，60%被垂向伸长消解。根据前人在东秦岭进行的岩浆岩、变质岩、地质年代学、地球化学及古地磁等研究，我们从构造角度证明了华南华北的聚合遵从剪刀式闭合的特征。在模拟过程中，优化了MOPLA模拟方法，加快了模拟速度，同时将应变量耦合到输入中，使模拟结果更加接近实际情况。