构造继承与陆内造山——以雪峰山湘南东安地区叠加构造为例

Intracontinental orogens often develop along weak zones inside continents. As an important expression of weak zones, pre-existing structures are considered as key to control formation and evolution of intracontinental orogens. However, inherited structures are easily modified by intense deformation of later tectonic events. The Mesozoic Xuefengshan Belt, as regarded as a classical intracontinental orogen, overprinted on an Early Paleozoic fold-thrust belt. Weak modification of widespread low temperature metamorphism and deformation preserved superposed structures, facilitating our structural analysis on pre-existing Early Paleozoic tectonics. This application focuses on the deformation variation above and beneath the regional unconformity in the Dongan superimposed structural zone, Xuefengshan, and implements multi-scale structural analysis and anisotropy of magnetic susceptibility of deformed rocks to resolve geometry and kinematics of low temperature polyphase deformation. Combined with calcite U-Pb dating method, we can obtain directly the deformation history of brittle structures to recover the Paleozoic deformation, the pattern of the Early Paleozoic fold-thrust belt. In comparison with the Mesozoic tectonics, we try to discuss the tectonic inheritance between the intracontinental orogeny and the pre-existing structures, and the controlling factor on the formation of this distinct belt.

陆内造山带通常沿大陆内部薄弱带形成。先存构造，作为薄弱带重要组成，被认为是控制后期陆内造山带形成与演化的重要因素。然而，依赖先存构造而产生的构造继承作用，往往因为后期事件的强烈改造而难以区分和识别。中生代雪峰山是一条典型的陆内造山带，发育在早古生代褶皱冲断带之上。广泛发育的中低温变形改造作用较弱，构造叠加关系保存较好，使得解析先存的早古生代构造成为可能；但同样中低温变形的复杂性也给分析增加了难度。本项目以雪峰山南部东安叠加构造区为靶区，将多尺度、精细构造解析与岩石磁化率各项异性研究相结合，精确限定中低温叠加变形中各构造要素的几何学、运动学特征；结合方解石U-Pb年代学等定年新方法约束中低温变形期次，恢复出早古生代构造变形；进而通过对比中生代变形，归纳叠加构造发育规律，探讨先存构造对中生代陆内变形的控制作用。

本项目以华南多期构造变形及其叠加改造的精确厘定为关键科学问题，聚焦华南内陆古生代和中生代构造变形叠加典型区域——雪峰山和九岭地区，开展了详细的构造解析、岩石变形分析和变形年代学工作，并结合岩石磁组构和重力反演等新手段，建立研究区的三维结构，划分出不同构造变形区域的几何学形态；并通过磁组构定量方法获得不同期次变形的展布，揭示晚期构造变形对早期变形的继承和改造。项目的重要结果有：（1）在雪峰山和九岭地区厘定出多期变形，包括早古生代上部向NNW挤压-右行走滑变形，早中生代上部向NW的挤压变形，以及晚中生代的NW-SE方向的伸展变形；（2）结合磁组构和年代学研究，建立了多期构造变形的时间序列和温度-构造变形-磁组构的对应关系；（3）对比早中生代挤压变形和晚中生代的伸展变形，我们发现在不同的应力场下，挤压构造更受控于先存构造的形态，伸展构造可以产生于力学强度相对较高的区域。项目执行期间，共发表10篇论文，其中国际SCI论文9篇。文章多发表在Tectonics、Tectonophysics等构造地质学权威杂志之上。我们建立的华南晚中生代周期性挤压伸展模型，受到广泛关注，并被Review of Geophysics、Geology、EPSL等顶级期刊引用；同时也受到不同学科专家关注，例如19年发表在Tectonics杂志上的文章，被多个矿床学团队正面引用（如Mao et al., 2021 Geology等），用来解释所研究的矿床背景和成因。