藏北改则及邻区新生代早期发育大型逆冲推覆构造系统,由不同方向的逆冲断层、不同时代的构造岩片、不同规模的飞来峰和构造窗、不同类型的褶皱构造组成.羌塘中部发育羌中薄皮推覆构造,石炭系板岩和二叠系白云质灰岩自北向南逆冲推覆于上白垩统与古近系红层之上,形成大型逆冲岩席和弧形逆冲断层,原地系统古近纪红层下伏三叠系—侏罗系海相烃源岩.羌塘南部发育南羌塘薄皮推覆构造,导致班公—怒江蛇绿岩、三叠系—侏罗系海相地层及侏罗纪混杂岩自北向南逆冲推覆于古近纪红层与下白垩统海相沉积岩层之上,形成三条蛇绿岩片带、大量飞来峰和厚度较大的构造片岩.中新世早期火山岩层和湖相沉积呈角度不整合覆盖逆冲断层、褶皱构造和逆冲岩席,不整合面上覆火山岩年龄为23.7~19.1 Ma,指示中新世早期改则及邻区基本结束了强烈逆冲推覆构造运动.估算羌中逆冲推覆构造的推覆距离约100~115 km,南羌塘逆冲推覆构造的推覆距离约82~110 km；新生代早期改则逆冲推覆构造系统近南北方向逆冲推覆总距离为182~225 km,对应地壳缩短率为(50.3±2.7)%.%Intensive thrusting occurred in the Gerze and its adjacent areas of northern Tibet in Early Cenozoic, forming the Gerze Thrust System consisting of thrust faults, tectonic slices and nappes, tectonic windows and accompanied folds. Southward thrusting of the Carboniferous slate and Permian dolomite limestone over the Late Cretaceous-Palaeogene red-beds and Triassic-Jurassic marine strata in Central Qiangtang Uplift formed the Central Qiangtang Thrust, whereas southward thrusting of the Bangoin-Nujiang ophiolites, Jurassic mélange and Triassic-Jurassic marine strata over the Palaeogene red-beds and Early Cretaceous marine sedimentary rocks in southern Qiangtang block formed the South Qiangtang Thrust. Early Cenozoic tectonic emplacement of ophiote slices along the South Qiangtang Thrust led to the formation of three ophiolite belts, accompanied by nappes and thrust sheets of Triassic sandstone and shale, Jurassic limestone and Jurassic mélange in the southern Qiangtang block. The Early Cenozoic thrusts were unconformably covered by the Early Miocene lacustrine deposits and volcanic rocks formed in 23.7~19.1 Ma, indicating that such intensive southward thrust stopped before Early Miocene in the Gerze and its adjacent areas. The minimal southward displacements of the Central Qiangtang Thrust and South Qiangtang Thrust are estimated to be ~100~115 km and ~82~110 km respectively, and the total southward displacement of the Gerze Thrust System is ~182~225 km, corresponding to crustal shortening of (50.3±2.7)% in Early Cenozoic Era.
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