滇东北会泽地区叠加褶皱特征及构造演化

Superimposed Fold Characteristics and Tectonic Evolution in Huize Area of Northeastern Yunnan,China

滇东北会泽地区位于扬子板块西南缘,发育小米落叠加褶皱。褶皱发育在小江断裂、会泽断裂、雨碌断裂所围限的三角区内,呈"弓"字形展布。小米落叠加褶皱野外特征反映小米落向斜经历了由轴迹近SN向至弯曲变形呈"弓"字形演化的过程。对会泽断裂及雨碌断裂进行详细野外解析,发现会泽断裂经历了由压性至右行压扭性再发展为左行压扭性的演化过程;雨碌断裂经历了由压性至右行压扭性转变的过程。应力场特征反映在区域应力作用下,受断层调整作用的影响,会泽地区依次受到近EW向、近NW向、和NE向挤压应力作用。通过对会泽及周缘地层接触关系进行分析,结合会泽地区新生代沉积盆地电子自旋共振(ESR)的年代学特征,确定了叠加褶皱形成时代为始新世晚期(25~38Ma),于渐新世晚期((17.8±1.7)Ma)和更新世(0.75~1.05Ma)被叠加改造。

Huize area in northeastern Yunnan is located on the southwest of Yangtze block, and outcrops Xiaomiluo superimposed fold. The fold is developed in the triangle area confined by Xiaojiang, Huize and Yulu faults, showing a “bow” shaped distribution. The stress field indicates that the syncline experiences a modification from a nearly SN-trending axis to a complex “bow” shape. Based on the detailed field analysis of Huize and Yulu faults, it is found that Huize fault undergoes transformations from compression to dextral transpression and then to sinistral transpression, while Yulu fault experiences an evolution from compression to dextral transpression. The characteristics of stress field show that faults adjust in response to the regional stress field, and Huize area undergoes compression in near EW-, NW-, and NE-trending directions successively. The strata contact relationship between Huize and surrounding areas along with the ESR chronological characteristics of Cenozoic sedimentary basin, determines that the superimposed fold occurs in Late Eocene（25-38 Ma）, and is superposed in Late Oligocene （17.8±1.7）Ma） and Pleistocene （0.75-1.05 Ma）, respectively.