柯街断裂北段的结构特征及地质意义研究

The structure characteristics and geological significance in the northern segment of Kejie Fault

柯街断裂是滇西地区重要的断裂之一,从早古生代开始就控制着断裂带两侧的地层沉积,但是目前关于柯街断裂还存在诸多争论.为了对柯街断裂的深部结构特征及地质意义进行研究,横跨柯街断裂布设了一条MT探测剖面,探测结果显示柯街断裂走向为NE向,根据二维反演电性结构断面图可以判断出在剖面上共有3个断层存在,推测断层F1和F2为柯街断裂北段的两个分支,其中断层F1规模大、切割深,断层F2规模相对较小;推测断层F3为岩性接触带.结合地层分布规律和岩性特征分析,发现断层F1东侧的晚奥陶统-早志留统仁和桥组地层上覆于西侧晚二叠统沙子坡组地层之上;在断层F2的深部,东侧新元古界允沟岩组地层上覆于西侧早石炭统香山组地层之上,在断层F2的浅部,东侧的晚白垩统花岗岩与西侧的早石炭统香山组地层相接触;断层F3上部的晚白垩统花岗岩上覆于新元古界允沟岩组地层之上.从而可以推断柯街断裂应为澜沧运动时期形成的逆冲断层,其中断层F2形成时期早于断层F1,断层F3为后期岩浆活动形成.综合柯街断裂北段两侧的电性特征和地质情况,认为柯街断裂是在澜沧运动过程中由保山板块和昌宁-勐连结合带汇聚并经过多期次的演化而成,在二叠纪以前很长一段时期控制着两侧的地层沉积,故本文认为柯街断裂应为保山板块和昌宁-勐连结合带的分界线.

Kejie fault is one of the important faults in western Yunnan,which controls the stratigraphy sedimentation on both side of the fault zone from the early Paleozoic,however,the understanding of Kejie fault is not very profound by now.In order to study the deep structure characteristics and geological significance of Kejie fault,we set up one survey line which across the Kejie fault for MT measure,the measuring result shows that the Kejie fault is NE trend,according to the deep electrical structure characteristics in northern segment of Kejie fault was obtained by MT,which shows that there is three faults in profile,inferring fault F1 and F2 are the two branches of the Kejie fault,in addition,the fault Fl is large-scale and deep cut,the fault F2 is smaller than Fl fault;The fault F3 maybe is lithology contact zone.Combined with the features of stratigraphic distribution and lithology,founding the Late Ordovician- Early Silurian Renheqiao Formation strata on the east side of Fl fault overlaying on the Late Permian Shazipo Formation strata on the wast side of Fl fault;In the deep of F2 fault,the Neoproterozoicthe Yungouyan Formation strata overlaying on the Early Carboniferous Xiangshan Formation strata,nevertheless,In the shallow of F2 fault,the Late Cretaceous granite contact with the Early Carboniferous Xiangshan Formation strata;In addition,the Late Cretaceous granite overlaying on the Neoproterozoicthe Yungouyan Formation strata,F3 fault exists between them.So we can deduce that Kejie fault is a thrust fault which formed in Lancang Movement,and the formation of fault F2 is earlier than fault Fl,fault F3 is formed by the late magmatic activity.Comprehensive the electrical characteristics and the geological conditions in the northern segment of Kejie fault,we think that the Kejie fault is formed by the plate convergence of the Baoshan plate and the Changning-Menglian suture zone,then it had experienced a multistage structural evolution after Lancang movement,which was controlling the stratigraphy sedimentation for a long time before the Permian,therefore,the Kejie fault should be the boundary between the Baoshan plate and the Changning-Menglian suture zone.