江南造山带中段地壳结构特征--来自武宁-吉安深反射地震随机介质相关长度分析的认识

Crustal Structure Characteristics of the Middle Part of Jiangnan Orogenic Belt:Insights from Random Medium Correlation Length Analysis of Wuning-Ji’an Deep Seismic Reflection Profile

江南造山带位于扬子和华夏地块中间,受华南陆块及其周缘多期次的碰撞、裂解及再造过程影响,经历了复杂的构造运动和变形,于中生代期间受区域构造-岩浆事件影响,发生成矿“大爆发”,是研究陆内深部过程、成矿作用的关键地区。受沉积覆盖、出露较少等因素影响,江南造山带中段地壳结构、深部过程及其边界范围等还存在争议。为进一步提高对江南造山带中段中生代深部构造背景、动力学过程及成矿作用的认识,本文利用武宁—吉安深反射地震数据,进行随机介质参数的计算,获得了相关长度剖面。结果发现江南造山带中段地壳厚度沿剖面由北向南逐渐减薄,结合前人研究推测研究区受控于燕山期晚期伸展构造体制,在伸展构造背景下,导致地壳减薄,诱发幔源物质上涌,受地幔上涌影响由南往北逐渐减弱。同时揭示了宜丰—景德镇断裂深大断裂极性,进一步证明了萍乡—广丰断裂为江南造山带中段与华夏地块的边界。最后综合分析了中生代区域构造对成矿的影响,认为在伸展构造背景下,幔源物质沿断裂上涌控制了该区金、钨等矿床的形成。

The Jiangnan orogenic belt is located in the middle of the Yangtze and Cathaysia blocks.It has experienced complex tectonic movements and deformations owing to the multi-stage collision,cracking,and reconstruction processes of the South China block and its periphery.During the Mesozoic era,it was affected by regional tectonic-magmatic events.The occurrence of the“big explosion”of mineralization is important in the study of deep intracontinental processes and mineralization.The Jiangnan orogenic belt is affected by factors such as sedimentary coverage and low exposure,and the crustal structure,deep processes,and boundary ranges of the middle part of the Jiangnan orogenic belt are still controversial.To further improve the understanding of the Mesozoic deep tectonic background,dynamic process,and mineralization in the middle part of the Jiangnan orogenic belt,in this study,we used the Wuning-Ji’an deep reflection seismic data to calculate the random medium parameters and obtain the correlation length profiles.The results showed that the thickness of the crust in the middle part of the Jiangnan orogenic belt gradually decreased from north to south along with the profile.Combined with the results of previous studies,it is speculated that the study area was controlled by the extensional tectonic system in the late Yanshanian period.The upwelling gradually weakened from south to north owing to the upwelling of the mantle.In addition,the polarities of the deep and large faults of the Yifeng-Jingdezhen fault were revealed,further proving that the Pingxiang-Guangfeng fault is the boundary between the middle part of the Jiangnan orogenic belt and Cathaysia block.Finally,the influence of Mesozoic regional structure on mineralization was comprehensively analyzed,and it is believed that under the background of extensional structure,the upwelling of mantle-derived material along the fault controlled the formation of gold,tungsten,and other deposits in this area.