大别山造山带中生代构造演化特征

Mesozoic tectonic evolutionary features of Dabieshan orogenic belt

大别山陆内造山带形成于早侏罗世晚期至早白垩世 (J31-K1) ,并具有分期演化特征。在构造演化序列上 ,可分出造山前期 (J21-J2 )和造山主期 (J3-K1) 2个阶段。构造变形方面 ,基本构造格局为一大型逆冲推覆系统组成的构造楔形体 ,呈后展式扩展 ,造成的地壳缩短量可达 46.8%。动力变质作用以高压动力变质为特征 ,发育高压动力变质岩 (榴辉岩、蓝片岩和高压麻粒岩 ) ,形成于构造应力集中的主干逆掩断层上盘。岩浆岩属钙碱性岩石系列、中酸性岩石组合 ,其中岩石类型、稀土元素配分型式等所反映的构造运动强度均具有一定的特点。在陆内造山带形成过程中伴生了 3期同造山磨拉石 :朱集期磨拉石 (J2 z)、段集期磨拉石 (J3d)和下符桥期磨拉石 (K2 x) ,它们反映了不同造山时期构造运动强度的差异。

The intracontinental orogenic belt of Dabieshan was formed in the late stage of Late Jurassic Early Cretaceous and characterized by periodical evolution features.The evolution can be divided into two stages according to the time evolutionary sequence,i.e.pre orogenic stage(J 2 1-J 2)and main orogenic stage(J 3-K 1).The fundamental tectonic framwork represents a huge tectonic wedge composed of a series of overthrust nappes which extends in overstep propogation.The shortening of crust caused by the deformation amounts to 46.8%.The dynamometamorphism is characterized by high pressure dynamometamorphic process,and high pressure dynamometamorphic rocks (eclogite,blue shist and high pressure granulite) are developed at the hanging wall of overthrust where tectonic stress is concentrated.Magmatic rocks belong to an association of calc alkaline and intermediate acidic rocks.The tectonic intensity reflected by the lithology and the distribution of REE is of certain own features.The formation process of the intra continental orogenic belt was accompanied by three generations of syn orogenic mollasses:Zhuji mollasse(J 2z),Duanji mollasse(J 3d)and Xiafuqiao mollasse(K 1x)which reflect the difference in tectonic intensity during different orogenic periods.