鄂尔多斯地块西缘科学山地区叠加变形分析

Superimposed Deformation Analysis in Kexueshan Area, the Western Periphery of Ordos Block, China

鄂尔多斯地块西缘科学山地区侏罗系地层发育典型的区域性叠加褶皱,记录鄂尔多斯地块西缘中生代以来主要构造演化过程。在区域性构造分析的基础上,通过野外构造解析,确定了两期构造缩短变形过程;同时运用层间滑动断层运动学分析,结合构造筛分,获得两期同构造缩短变形的挤压构造应力场;综合区域构造与构造年代学,提出科学山地区晚中生代以来两期构造演化过程。中—晚侏罗世(J_2—J_3)受NW—SE向构造挤压作用控制,鄂尔多斯地块西缘科学山地区发生NW—SE向构造缩短变形,形成NE—SW向的褶皱构造与相关的逆冲断层,同时控制了中—上侏罗统沉积。这期构造缩短变形可能是西伯利亚板块向南汇聚与太平洋板块NW向俯冲联合作用的结果。中新世晚期—上新世晚期(N■—N_2)挤压构造应力场转变为NE—SW向构造挤压,导致NW—SE向褶皱构造发育,并叠加在早期NE—SW向构造之上,形成区域性叠加褶皱。区域构造分析表明,这期构造缩短变形是青藏高原NE向扩展的构造响应。上述研究为重建鄂尔多斯地块西缘陆内变形过程提供了重要证据。

Kexueshan area in the western periphery of Ordos block is characteristic of typical regional superimposed folds in Jurassic strata, documenting the main tectonic evolution process since Mesozoic in the western periphery of Ordos block. On the basis of regional structural analysis, the two-phase structural shortening deformation processes in this area were determined by field structural investigation. Meantime, the two-phase tectonic stress fields related to the structural shortening deformation were reconstructed by using fault kinematic analysis in Kexueshan area, together with structural sieving. Synthesizing the regional structural analysis and geochronology, two stages of tectonic evolution were proposed since Late Mesozoic in Kexueshan area. During Middle-Late Jurassic(J2-J3), under the control of NW-SE trending tectonic compression, the NW-SE structural shortening deformation occurs in Kexueshan area, which forms the NE-SW trending folds and thrust faults, and controls the Middle-Late Jurassic deposits. This structural shortening deformation is likely liked with a combination of the southward convergence of the Siberian plate and the northwestward subduction of the Pacific plate. During Late Miocene-Late Pliocene(N■-N2), the tectonic stress field is transformed into NE-SW trending tectonic compression, resulting in the development of the NW-SE trending folds, which are superimposed on the early NE-SW trending folds, and featured by regional superimposed folds. Regional structural investigation shows that this structural shortening deformation coincides with the northeastward growth of Qinghai-Tibet Plateau. The above studies provide important evidence for the reconstruction of the intracontinental deformation process in the western periphery of Ordos block.