蒙古-鄂霍茨克构造带中段构造变形及动力学特征

摘要

As an important part of the Central Asian Orogenic Belt, the Mongolia-Okhotsk collisional belt has attracted much attention for its tectonic deformation and dynamic characteristics. Along the middle part of the Mongolia-Okhotsk collisional belt, five ductile deformation sites and a brittle deformation site were analyzed to reveal its tectonic deformation and dynamic features. B style fold, crumple structure, A style fold, mineral stretching lineation and S-C fabric indicate NW-SE shearing. This information reveals that might have existed a large collision or multi-periodic collisions in the same direction, which resulted in the formation of the Mongolia-Okhotsk collisional belt. The forming time and global tectonic settings as well as the dynamic origin of the Mongolia-Okhotsk collisional belt were discussed. This tectonic belt was mainly formed during the middle Jurassic-early Cretaceous period under the tectonic setting of the East Asian multi-direction convergence. The brittle deformation of Site mg6 was analyzed and two paleo-stress fields were restored, i.e., the NW-SE compression stress field and the E-W compression stress field. The NW-SE compression stress field might have resulted from the distant effect of the westward subduction of the Paleo-Pacific plate during the Jurassic and Cretaceous, whereas the E-W compression stress field probably resulted from the distant effect of the India-Asia collision during the early Cenozoic.%蒙古-鄂霍茨克构造带作为中亚造山带的重要组成部分，其构造变形和动力学特征一直是地质界关注的问题。沿着该构造带中段，对5个韧性变形点及1个脆性变形点进行详细解析，揭示了该构造带变形及动力学特征。B型褶皱、揉皱、A型褶皱、矿物拉伸线理、S-C组构都显示了该构造带明显的NW-SE剪切作用。剪切方向稳定而单一，未发现多方向变形叠加现象，可能指示了蒙古-鄂霍茨克构造带的形成过程为一期主要的俯冲碰撞或多期同向的俯冲碰撞。对蒙古-鄂霍茨克构造带形成时间和动力学背景进行了讨论，认为该构造带主要形成于中晚侏罗世-早白垩世东亚多向汇聚动力学背景之下。对构造带内地质点mg6脆性断层面上滑动矢量进行了统计和古应力场反演，得出两期古构造应力场，一期为NW-SE挤压，一期为近E-W挤压。NW-SE挤压应力场可能对应了中晚侏罗世-白垩纪古太平洋板块向西俯冲对中亚地区的远程影响；而近 E-W 向挤压可能反映了早新生代印度-欧亚板块碰撞对中亚地区的远程效应。