基于布格重力数据研究郯庐断裂带江苏段深部构造

Deep structures of Jiangsu segment of Tan-Lu fault zone derived from bouguer gravity data

本文收集了郯庐断裂带江苏段及周边地区的布格重力数据,利用小波多尺度分析方法对该地区的重力场进行场源分离,深入研究了区域地壳密度结构及断裂空间展布特征,并应用Parker密度界面模型对区域莫霍界面进行反演分析.研究结果如下:(1)布格重力场显示,郯庐断裂带江苏段形成了NNE走向的大型的重力高异常条带及重力梯度带,分隔了华北板块和苏胶块体、下扬子板块,成为区域内重要的地球物理分界线;(2)小波重力细节场揭示,沉积层及上地壳结构复杂,郯庐断裂带的5条主干断裂形成线性异常条带贯穿区域中央,控制着断裂带内部的隆凹构造单元.中下地壳结构相对简单,郯庐断裂带形成宽缓的高、低异常区,洪泽-沟墩断裂、淮阴-响水口断裂、宿迁-无锡断裂等深大断裂与之交切,而邵店-桑墟断裂不与之相交.受宿迁-无锡断裂交切的影响,郯庐断裂带江苏段在宿迁地区出现明显的分段性;(3)区域莫霍面形态东高西低,郯庐断裂带形成了莫霍面陡变带,造成了东西分异的格局,泗洪地区出现莫霍面局部上隆区,可能由于软流层或上地幔高密度物质上隆所致.

In this paper, the wavelet multi-scale analysis method was applied to separate gravity field to study the crustal density structures and fault distribution of the Jiangsu segment of the Tan-Lu fault zone based on the bouguer gravity data with sample intervals of 2 km. And the Parker variable density model was utilized to inverse the Moho interface. Results indicate that Jiangsu segment of Tan-Lu fault zone behaves NNE striking large-scale gravity anomalies and the gravity gradient zone, which separate the North China plate from the Sujiao block and the lower Yangtze plate. The detailed gravity fields show that structures of the sedimentary layer and the upper crust are complex, and the Tan-Lu fault zone is composed of five secondary faults with linear gravity anomalous belt, which controls the uplifting and depressional tectonic units in this region. Comparatively speaking, structures of the middle and lower crusts are much simple. In these layers, the Tan-Lu fault zone intersects with the Hongze-Goudun fault, Huaiyin- Xiangshuikou fault and Suqian-Wuxi fault, where presents gentle and wide high- and low-gravity anomalies. Influenced by the intersection with SuqianWuxi fault, Jiangsu segment of Tan-Lu fault zone is composed of many sub sections in Suqian area. However, the Tan-Lu fault zone does not intersect with Shaodian-Sangxu fault in the middle and lower layers. The Moho interface descends greatly across the Tan-Lu fault zone from the east to the west, forming a gradient belt inclined to the west. The Moho interface uplifts greatly beneath Sihong area which is considered to be induced by the upwelling of high density materials from the uppermost mantle and asthenosphere.