南天山造山带中段推覆体内部变形及其与逆冲构造的关系

南天山造山带是古生代期间塔里木板块与伊犁—伊塞克湖板块对接、碰撞的产物 ,主体由向南逆冲的推覆体组成。推覆体内部变形构造在垂直于主断面方向上呈规律性变化。从推覆体底部向上 ,褶皱从 A型褶皱 ,紧闭、等斜的 B型褶皱 ,前翼褶皱经斜歪、倒转褶皱渐变为对称的尖棱或箱状 B型褶皱 ;构造面理从发育主断面近平行的 S-面理及剪切滑移的 C-面理渐变为只发育与主断面近垂直的 D-面理。据此 ,可把推覆体自下而上划分成为递进剪切、过渡和等轴挤压三个变形域。变形过程分析表明 ,存在水平挤压变形和随后的简单剪切变形两个变形阶段 ,前者发育于主断裂面形成之前 ,后者发育于主断裂面形成之后。这指示南天山造山带以变形扩展速率高于断裂扩展速率为特征

INTERNAL DEFORMATION OF THE NAPPESIN THE MIDDLE PART OF SOUTH TIANSHAN OROGEN AND ITS RELATIONSHIP TO THRUST STRUCTURES

South Tianshan orogen,resulted from the collision between Tarim and Yili- Issyk plates in Paleozoic,is mainly composed of thurst nappes.Antomy of Small- scale deformational structures show a clear deformation developing pattern within individual nappe.From bottom to upper of a nappe,small- scale fold types change gradually from A- folds,inclinal or tight recumbent folds to symmetric chevron- and/or box- folds,with close overturned folds as their transitional type;S- foliation,solution cleavage,changes its attitude from parallel to vertical to the main thrust,and C- foliation,a shear- slide cleavage,developed only in the bottom of individual nappes froming type S- C tectonite.Based on the above deformation features,three deformation domains,progressive shear- ,transitional- and coaxial compression- deformation domain from lower to upper,can be distinguished in an individual nappe.Analysis on deformation path indicates that the nappe expierenced a foregoing coaxial compressive deformation stage developed before the formation of main thrust, and subsequent simple shear deformation stage deveolped after the formation of the main thurst.This suggests that the deformation in South Tianshan orogen is characterized by deformation progress which is faster than fault progradation.