中蒙边界中生代推覆-伸展递进转换及地壳尺度的切向剪切  

Mesozoic progressive transition from overthrusting to extension in the Sino-Mongolian border region and crustal-scale tangential shear

作　　者：王涛[1] 郑亚东[2] 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]北京大学地质系,北京100871

出　　处：《地质通报》2002年第4期232-237,共6页Geological Bulletin of China

基　　金：国家自然科学基金(49872072);中国博士后科学基金资助。

摘　　要：中蒙边界一带发育中生代大型推覆和伸展构造。亚干伸展变质核杂岩从开始形成到最终(早白垩世)成型是一个长期递进发育过程,早期深层次透入性韧性伸展剪切主要发生于170～135Ma,有迹象显示在228～170Ma已经开始。这与中生代推覆事件在时代上重合,且运动指向相同,即上盘均向南东,显示推覆与伸展同时、同向的递进转换。提出地壳尺度切向剪切构造模式:在上地壳近水平简单剪切和水平挤压叠加构成一般剪切而形成推覆;而在中下地壳近水平简单剪切和上下挤压(重力作用)叠加构成一般剪切而发育同向伸展拆离剪切带(C'),随着上地壳的增厚和下地壳的减薄,该伸展剪切带向上扩展形成变质核杂岩。Mesozoic large-scale thrust nappe and extensional structures occur in the Sino-Mongolian border region.The initiation to final shaping of the Yagan extensional metamorphic core complex were a lengthy progressive development process.The early deep-level penetrative ductile extensional shear mainly took place at least at170～135Ma and may have started as early as228～170Ma .The timing is consistent with that of the Mesozoic overthrusting event.Both the extension and overthrusting show the same shear sense,i.e.the upper plate(hanging wall)was south-vergent ,suggesting the synchronous progressive evolution of extension and overthrusting in the same vergence.On that basis a crustal-scale tangential shear model is proposed,in which overthrusting occurs in the upper crust owing to the superimposition of subhorizontal simple shear on horizontal compression and synthetic extensional shear zones(C' )occur in the middle-lower crust owing to the superimposition of subhorizontal simple shear on vertical compression(gravity ac-tion)and the C' propagate upward into the extensional detachment zones with thickening of the upper crust and thinning of the lower crust,leading to the formation of a metamorphic core complex.

关 键 词：切向剪切 构造层次 推覆-伸展转换 变质核杂岩 中生代 中蒙边界 

分 类 号：P542[天文地球—构造地质学] P534.5[天文地球—地质学]