米仓山构造带逆冲-走滑变形序列的节理研究

Thrust and strike-slip deformation sequence of Micangshan structural belt

米仓山构造带位于扬子板块北缘,东西两侧分别同龙门山、南大巴山冲断带交接过渡,由于受到多个造山带的影响,所以对其构造复合过程的研究至关重要。文中通过测量米仓山构造带的节理面和擦痕,采用吴氏网对古应力场进行恢复,同时依据节理缝的交切关系以及节理面所在地层时代,结合已有年代学资料和断层特征,首次重建了米仓山构造带的构造期次。米仓山构造带共经历了5期构造运动:①200～160Ma,S—N向(σ3直立)逆冲性质挤压运动;②120～100Ma,S—N向(σ3E—W向)走滑性质挤压运动;③95Ma,NW—SE向挤压运动;④50～40Ma,NE—SW向挤压运动;⑤15Ma,E—W向挤压运动。第一期、第二期应力场形成了米仓山隆起和米仓山前缘的东西向构造,第三期、第四期应力场对米仓山构造带进行改造,形成了米仓山前缘的叠加构造,第五期应力场使米仓山构造带最终成型。

Micangshan structural belt is located in northern margin of Yangtze plate,which has transition relations with Longmen Mountain in west and south Daba Mountain in east.Under the multiple geodynamics of its peripheral orogenic belts,the study on structure and evolution of Micangshan structural belt is very important.Based on joint plane and scratch measured in Micangshan structural belt,Wulff net is applied to recover the palaeostress field.According to the intersection relation of joint fissures and the chronologic age of joint plane,combining with existing chronology data and fault features,the structure evolution of Micangshan structural belt is reconstructed firstly.Micangshan structural belt experienced five phases of tectonic movement：① From 200 Ma to 160 Ma,N-S thrusting compressional movement;② From 120 Ma to 100 Ma,S-N strike-slipping compressional movement;③ 95Ma,NW-SE compressional movement;④ From 50 Ma to 40 Ma,NE-SW compressional movement;⑤15Ma,E-W compressional movement.In generally,the first and second phases of palaeostress field formed the Micangshan uplift and the E-W structures in the front area of Micangshan,the third and fourth phases of palaeostress field superimposed the early structures and then formed superimposed structures in the front,and the fifth phase of palaeostress field finally make the Micangshan structure belt formed.