藏南嘉黎断裂古乡—通麦段多期活动特征及其构造意义

嘉黎断裂是青藏高原南部呈北西西—南东东向喀喇昆仑—嘉黎断裂系的重要组成部分,被认为代表了北拉萨地块和中拉萨地块之间的构造界线。关于嘉黎断裂的构造性质和演化过程等仍存在争议,其不同期次构造过程仍需要进一步研究。在详细的区域地质填图基础上,以嘉黎断裂古乡—通麦段为研究对象,重点调查了该断裂带不同期次变形的几何学与运动学特征,基于新获得的不同方位断层面与擦痕特征等资料,恢复和计算该区的不同期次应力场及方向,并据此解析该区的多期构造叠加关系,探讨嘉黎断裂在不同应力场下的多期活动特征以及相关的区域构造演化过程和大地构造背景,在此基础上讨论了嘉黎断裂对拟建铁路工程的影响。研究结果显示,嘉黎断裂晚新生代以来仍有活动迹象,并具有多期构造叠加特征,从早到晚依次为左旋走滑(D₁)、正倾滑(D₂)和右旋走滑(D₃)。嘉黎断裂作为东喜马拉雅构造结地区重要的变形调节构造,其多期活动性质反映了地块间的相对运动特征及区域应力场的转换过程,这对认识青藏高原南缘的新生代构造演化过程具有重要意义。

Multi-stage Characteristics and Tectonic Significance of the Jiali Fault in Guxiang-Tongmai Section,South Tibet

The Jiali fault is an important part of the WNW-ESE trending Karakorum-Jiali fault system in the southern Tibetan Plateau,which is considered to be an ancient suture zone between the north Lhasa and the central Lhasa block.However,the tectonic properties and deformation ages of the Jiali fault are still controversial and need further study.Based on detailed regional geological mapping,our work focused on the Guxiang-Tongmai section of the Jiali fault,especially on investigating the geometric and kinematic characteristics,and subsequently on restoring and calculating the stress field and their direction in different periods,based on the newly identified fault planes and striations of different directions.Accordingly,we analyze the superimposing structural relations of this area,and discuss the multi-stage activity characteristics of the Jiali fault under different tectonic stress fields,and the regional tectonic evolution and background.Consequently,the influence of the Jiali fault on the proposed Sichuan-Tibet railway line was discussed.Results indicate that the Jiali fault is active from the Late Cenozoic,and show tectonic superimposed characteristics,including(from early to late)the sinistral strike-slip fault(D1),normal fault(D2)and dextral strike-slip fault(D3).As an important accommodation structure of the eastern Himalayan syntaxis,the multi-stage deformation of the Jiali fault zone reflects the relative movement of adjacent blocks and the regional tectonic stress field conversion,which is of great significance for understanding the Cenozoic tectonic evolution of the southern margin of Tibetan Plateau.