川东北何家营地区三维构造模型:来自高精度线束三维资料的约束

3D structural model of the Hejiaying area, northeastern Sichuan Basin:Constraint from highresolution linebound 3D seismic data

川东北地区方斗山构造带发育典型的多重滑脱构造,中生代以来受大巴山南北向挤压与雪峰山北西向挤压叠加改造。其构造模型在区域性滑脱层的分布,不同构造变形层构造样式的厘定以及不同构造变形层在空间上耦合特征等方面存在争议,因此定量分析不同变形层构造样式的差异、空间组合特征成为研究分层变形成因机制的关键。本文应用数字高程、浅表地质信息与线束三维地震数据等资料,开展方斗山北段何家营地区地层与断裂构造解析,建立了何家营地区的三维构造模型,讨论方斗山北段多重滑脱层体系下,垂向上不同构造变形层的差异变形特征及其控制因素。研究表明:何家营地区沉积盖层中存在中-下寒武统膏盐层、下志留统泥岩层、下三叠统嘉陵江组膏盐层等3套区域性滑脱层以及二叠系煤层局部滑脱层。区域性滑脱层控制了褶皱—冲断构造的变形样式,构造在垂向解耦,形成基底、深部、中部与浅部等4套变形层。基底变形层发育指向北西的构造楔;深部变形层夹持于寒武系与志留系滑脱层之间,发育双重构造,形成低幅度背斜;中部变形层为志留系与嘉陵江组之间的高角度冲断构造,二叠系煤层作为局部滑脱层,发育顺层剪切;浅部变形层,以嘉陵江组盐滑脱褶皱为主。不同变形层的垂向叠置,共同形成了现今的高陡背斜。不同构造变形层地层能干性组合与缩短量的差异决定了构造样式的差异。软弱层传递位移,中寒武统膏盐层、志留系页岩与下三叠统膏盐层,缩短量最大,变形最强,是控制区域变形的主要滑脱层。何家营地区发育倾向南东的基底断层,不同变形层的主干断层与褶皱轴迹方向一致,均以北东、北东东向为主,反映出何家营地区构造变形主要受控于来自雪峰山方向的挤压作用。

The Fangdoushan anticline belt in the northeastern Sichuan Basin is characterized by typical thin-skinned multi-level detachment structures, which have been superimposed by the compression of Daba Mountain and Xuefeng Mountain since the Mesozoic. Regional detachment layers, the delineation of structural styles of different structural layers, and the spatial coupling among the different structural units are still controversial. Therefore, quantitative analysis of spatial combination features and differences of different structural units is the key to understanding the mechanism of multiple detachments in the area. Based on the theory of fault-related folding theory,combined digital elevation model, surface geological information, and high resolution line-bound 3D seismic data to construct the geological structure model of the Hejiaying area, the northern part of Fangdoushan anticline in 3D space, discuss the differential deformation characteristics of different structural layers and their controlling factors under the multi-layer detachment. The results show that it develops three regional detachment layers including the Middle and Lower Cambrian gypsum layer, Lower Silurian mudstone layer, and Lower Triassic Jialingjiang Formation gypsum layer. The regional detachment layers control the structural styles of the fold-thrust structure which is decoupled vertically to form four sets of structural layers: base, deep, middle, and shallow levels.The base level forms a wedge. The deep level is controlled by Cambrian and Silurian detachment layers, duplex is developed to form low-amplitude anticlines;the middle level is controlled by the Silurian detachment layer, forming high-angle brittle thrusts. And the Permian coal seam is a local detachment layer and developed bedding shear. Shallow level is affected by the thrust of the middle level and is characterized by detachment folds and salt-related structures in the Jialingjiang Formation. Differences in the combination of mechanical stratigraphy and shortening in different structural units determine the differences in structural styles. Weak layers transmit displacement with the largest shortening and the strongest deformation. Regional detachment layers with the maximum shortening and the strongest deformation, control regional deformation. The superimposed deformation of different structural units controls uplift in the Hejiaying area. The basement faults in the Hejiaying area tend to the southeast, and the strikes of main faults of different levels are in the same direction as the fold axis trace, which is mainly NEE and NEE, indicating that the tectonic deformation in the Hejiaying area is mainly strongly affected by the compression from Xuefengshan thick-skinned belt.