Abstract: The Zhonggu Fault,located in the Yuanjiang-Yuanyang basin and active strike-slip fault since Neogene,is part of the southern segment of the Red River Fault.Its neotectonic movement resulted in the separation of the Red River basin(a Miocene basin)into two sub-basins and a dextral slip extending to the Guotoushan-Damanmi region.The concomitant mountain frontal fault,which was the dominant fault in Oligocene,is of normal faulting.Its activity resulted in the accumulation of red continental clastic sediments in the eastern and northeastern Yuanyang.The mountain frontal normal fault extended to the northwest of Honghe County and formed the deposition of conglomerate in early Miocene.Along the Zhonggu Fault,which offset Miocene sediments with high angles,the geological features,including the compressive fold with axis trending NE,the compressional deformation landforms,the distribution the Miocene to Quaternary sediments migrating from SE to NW successively and their delayed distribution at the northeastern wall of the Zhonggu Fault,all suggest that the southern segment of the Red River fault has been expanding from SE to NW and there has been the dextral strike-slip faulting since Miocene.The geological evidences,such as thick lower-mid Miocene conglomerate deposited in mountain front,the shear deformation involved in Zhonggu Fault which was more intense in Miocene than that in Pliocene,the shear zone of Zhonggu Fault mainly located in lower-mid Miocene sediments,indicate the large scale dextral slip occurring at mid Miocene,and its fission track age is 13.7Ma.The magnitude of dextral offset on the south segment of Red River Fault since Miocene was calculated by multiple means,e.g.the horizontal dimensions of the offset of Miocene sediment,the length of foreland basin and deformation width relating to the Zhonggu Fault slip,and the relationship between the offset and width of fault,with the result ranging from 62～69km(the mean is 65km).The data also suggest that dextral slip of the Red River fault experienced the process of transition(N₁),initial dextral slip(N₁²),large scale dextral slip(N₁³—N₂¹),and dextral slip propagation(N₂²—Q_p¹)phases.The related activity of the Red River fault altered between shear slip and extensional slip.

Key words: stratum and tectonic deformation, propagation style of basin, dextral slip and offset, south segment of Red River Fault, Yunnan

摘要： 红河断裂带南段(元江—元阳一带)穿经盆地内的"中谷断裂",是一条新构造期明显活动的主平移断裂。它的新近活动将中新世红河盆地一分为二,右旋切错至倮头山—大曼迷一带。与此相伴,山前断裂则以正断活动为主。沿"中谷断裂"高角度切错中新统的剪切走滑断面,被断错的中新世条形盆地内发育轴向NE的挤压褶皱及压缩变形的空间变化特征,下中新统、中上中新统、上新统及第四系的分布依次自SE向NW有序迁移且在"中谷断裂"的东北盘节节错后分布等,均表明红河断裂南段中新世以来自SE向NW的不断破裂扩展和右旋走滑位错;区段内中下中新统较厚的山前磨拉石沉积建造、卷入"中谷断裂"剪切变形的强度中新统明显强于上新统等表明,红河断裂南段大规模的右旋走滑运动应发生在中中新世前后,其FT年龄约为距今13.7Ma;根据切错的中新统的平面尺度、用平衡剖面法恢复压缩前盆地的长度和由断层变形带宽度等计算,求得红河断裂带南段中新世以来大型右旋位错总量介于62～69km,中值为65km。研究资料还表明,红河断裂右旋走滑运动作为一个过程,经历转换活动期(N₁)、右旋走滑初始期(N₁²)、大型右旋走滑期(N₁³—N₂¹)和右旋走滑扩展期(N₂²—Q_p¹)等多个发生、发展与演化阶段。与其相应的断裂活动性质也存在着从剪切走滑—张性走滑不断交替的转换过程。

关键词: 地层与构造变形, 盆地扩展方式, 右旋位错运动与位错量, 红河断裂带南段, 云南