华南地区构造-岩浆活化与热液铀成矿的分形动力学

摘要

South China includes two typical Cathysian Diwa regions (i.e., Southeast Diwa and Kiangnan Diwa regions). The complicated multi-stage tectono-magmatic evolution resulted in the widespread granites, and Mesozoic-Cenozoic rifted basins, as well as NE-NNE and NW trending deep faults, and led to the formation of numerous hydrothermal uranium ore deposits. Fractal analyses and numerical simulation of the spatial distribution of faults, granite bodies and uranium ore deposits with fractal distribution were used to discuss the tectono-magmatic activization and fractal dynamics of hydrothermal uranium mineralization in South China, based on the theories of polygenetic compound and tectonic unit metallogeny. The calculated box counting dimensions of faults from Southeast Diwa and Kiangnan Diwa regions were 1.6800 and 1.5939, respectively, indicating that the faults in the former region are favorable for uranium mineralization. The calculated box counting dimension (D) and perimeter-area fractal dimension (DPA) of the granite bodies emplaced during Precambrian to late Yanshanian periods indicated that the D values increase with the granite outcrop area while DPA values increase with the granite shape complexity, demonstrating the strengthening complexity of tectono-magmatic activization. In addition, the D and DPA values of the granite bodies during the periods of Late Yanshanian, Early Yanshanian and Indosinian were relatively high, demonstrating that they also facilitated uranium mineralization. On the other hand, the calculated values (i.e., 1.0254) of box counting dimension of hydrothermal uranium ore deposits in South China are significantly lower than that of faults, consisting with the low distribution density and enrichment of uranium ore deposits. Our simulated results of Cellular Automata Model show that the fractal dimension values of faults and mineralization increase with time, and the large-scale mineralization occurs when these values reach the critical condition of fractal penetration during the mid-late stage simulation. Overall, the fractal evolution of complicated multi-stage tectono-magmatic activization in the two typical Cathysian Diwa regions produced the fractal distribution characteristics of polygenetic compound hydrothermal uranium deposits in South China.%华南地区位于东亚壳体东南缘,包括东南地洼区和江南地洼区两个典型的华夏型地洼区,该区多阶段的复杂构造–岩浆演化形成了大量的花岗岩及断裂构造,并导致大量多因复成热液铀矿床的形成。这些花岗岩体、断裂构造及铀矿床的空间分布均具有分形特征。东南地洼区断裂构造的分维值为1.6800,明显大于江南地洼区的1.5939,显示前者更有利于热液铀成矿作用的发生。花岗岩体空间分布盒维数 D 总体上随其规模增大而增大,较大的周长–面积分形维数 DPA会导致盒维数 D 增大,显示其构造–岩浆活动的复杂性增强。其中燕山晚期、燕山早期和印支期较大的 D 和 DPA 显示其更有利于热液铀成矿的发生。华南地区热液铀矿床空间分布盒维数为1.0254,明显小于两个不同构造区断裂构造空间分布的分维值,表明华南地区铀矿床的发育程度低于断裂。用元胞自动机模型对断裂和成矿演化进行模拟的结果表明,其分维值随时间逐渐增大,到中晚期断裂分维值增高至超过临界值后才有大规模成矿作用发生,成矿分维值显著增大。多阶段复杂的构造–岩浆活动的分形演化导致了华南地区多因复成热液铀成矿的分形分布。