大娄山构造带茅台向斜中-新生代多期叠加改造变形特征

中国西南地区是地震灾害的频发区,研究该地区的构造变形特征,对认识西南地区地震等灾害的发育机理具有重要意义。大娄山构造带位于四川盆地东南缘,该构造带发育了复杂的构造变形样式,记录了中-新生代以来华南板块构造变形的详细信息。茅台向斜位于大娄山构造带内部,发育了典型的叠加褶皱构造样式,该样式是揭示大娄山构造带中-新生代构造变形特征的关键。在前人研究的基础上,本文通过对茅台向斜的构造解析,认为茅台向斜中-新生代以来经历了三期挤压变形过程。第一期(D1)表现为在侏罗系及其以下地层中发育走向近NE-SW的向斜构造,古应力场反演结果表明受到近NW-SE向挤压作用,结合区域性角度不整合及卷入变形的最新地层,该期构造变形发生于侏罗纪末期,其动力来源于古太平洋板块的俯冲作用。第二期(D2)变形表现为对早期近NE-SW向褶皱构造被NE-SW向挤压作用的叠加改造,古应力场反演结果表明受到NE-SW向挤压作用,结合区域角度不整合特征,该期构造变形发生在古近纪末期,其动力来源于青藏高原初期的向外隆升扩展。第三期(D3)构造变形特征表现为近N-S向挤压构造的发育,结合区域性角度不整合及卷入变形的最新地层,该期构造变形时间为新近纪末期,其动力来源于青藏高原的向东逃逸扩展。

The polyphase of superposed deformation of Maotai Syncline during the Meso-Cenozoic time, Daloushan Tectonic Belts

The Daloushan tectonic belt is located at the southeast margin of the Sichuan Basin, at the junction of the Yangtze plate and the Cathaysia plate, which records the history of plate tectonics deformation in South China in detail. The Maotai Syncline is a typical superimposed fold structure located in the Daluoshan tectonic belt, which is the key to revealing the characteristics of Mesozoic and Cenozoic tectonic deformation in the Daluoshan tectonic belt. In this paper, the geometric, kinematic and dynamical characteristics of the Maotai Syncline are analyzed through the tectonic analysis of the Maotai Syncline. Together with regional geological research, the Maotai syncline has been involved into three phases of shortening deformation since the late Mesozoic. The first phases (D1) is represented by the near NE-SW syncline developed within the Jurassic system and its lower strata. Paleostress field inversion results indicate near-NW-SE compression. Together with the regional of angular unconformity and the latest strata involved in the deformation, this phases of tectonic deformation occurred at the end of the late Jurassic, and It is driven by the subduction of the ancient Pacific plate. The second phases (D2) deformation is represented by the superposition and transformation of the early NE-SW fold structure by the NE-SW shortening. Paleostress field inversion results indicate NE-SW compression. Together with the regional angle unconformity characteristics, it shows that the structural deformation of this phases occurred in the late Cretaceous, and It is driven by the outward uplift expansion of the Tibetan Plateau in its early stages. This third phase (D3) of tectonic deformation is characterized by the development of nearly N-S trending compression tectonics. Together with the regional of angular unconformity and the latest strata involved in deformation, this tectonic deformation occurred at the end of the Paleogene period, driven by the eastward escape expansion of the Tibetan Plateau.