川东与大巴山褶皱冲断带交汇区构造几何学和运动学特征

川东与大巴山褶皱冲断带交汇区位于四川盆地东北缘,由温泉井—马槽坝背斜带、云安场背斜带和方斗山背斜带组成,其形成过程受川东构造带和大巴山构造带的双重控制,开展川东与大巴山褶皱冲断带交汇区构造几何学和运动学特征研究,对认识华南板块和华北板块之间的拼贴碰撞及演化具有重要意义。本文基于野外调查、钻测井资料和二维地震资料,以断层相关褶皱理论为指导,通过对四条二维地震剖面的精细解析,揭示了交汇区构造几何学特征,并应用2Dmove软件恢复了研究区构造运动学过程。研究认为:①交汇区在南北方向上显示为大型的复向斜结构,垂向上被区内下三叠统嘉陵江组膏盐层、志留系泥页岩层和下寒武统泥页岩层三套滑脱层分为上、中、下三大构造层,上构造层主要发生滑脱褶皱变形,中、下构造层发育断层较多,主要发育双冲构造、冲起构造以及断层转折褶皱;②研究区中构造层构造变形最为强烈,构造缩短率达10%,上、下构造层构造缩短率较小,均为6%左右,且各构造层缩短率由西到东呈现出逐渐增大的趋势;③中生代以来,研究区的构造演化过程分为三个阶段:晚三叠世到晚侏罗世稳定沉积阶段、早白垩世到古近纪早期对冲变形阶段、古近纪晚期至今定型阶段。

The geometry and kinematics of the intersection area of eastern Sichuan and the Dabashan fold- thrust belt

The intersection area of eastern Sichuan and the Dabashan fold- thrust belt is located in the northeastern Sichuan Basin and is composed of the Wenquanjing- Macaoba anticline belt, the Yunanchang anticline belt and the Fangdoushan anticline belt. The formation and evolution of the intersection area is controlled by the eastern Sichuan structural belt and the Dabashan structural belt. Therefore, this study is relevant for understanding the collision between the South China plate and the North China plate and its subsequent evolution. Based on field investigations, drilling data, logging curves and 2D seismic data, guided by fault related folding theory, this paper reveals the geometric features of the intersection area with four seismic profiles which were precisely interpreted to reconstruct the tectonic kinematics process of the study area by using 2D move software. This paper concludes that: (1) the intersection area shows a giant synclinorium structure in the south- north direction and can be divided into three vertical structural layers by three detachment layers; the gypsum- salt bed of Lower Triassic Jialingjiang formation, the mudstone and shale of the Silurian, and the mudstone and shale of the Lower Cambrian. The upper structural layer mainly occurs as decollement, whereas there are many faults in the middle and lower structural layers where duplex structures, pop- up structures and fault- bend folds developed. (2) In the study area, the deformation of the middle structural layer is the strongest, with a structural shortening rate of 10%; the shortening rates of about 6% in the upper and lower structural layers are relatively small. Also, the shortening rate of each structural layer gradually increases from west to east. (3) Since the Mesozoic, the evolution of the study area has been divided into three stages: stable sedimentary stage from the late Triassic to the late Jurassic, opposite thrusting stage from the early Cretaceous to the early Paleogene, and the shaping stage from the late Paleogene to the present.