塔里木盆地西南缘构造样式及其主导因素

Structural styles in south-western margin of Tarim Basin and their dominate factors

塔里小盆地西南缘是西昆仑山前北北西—近东西向的构造变形带。具有南北3带、东西3段、上下3层的展布特点。各带、段和层以基底卷入的冲断构造和盖层滑脱的断层相关褶皱为主,包括:破冲褶皱、断层扩展褶皱、断层滑脱褶皱和断层弯曲褶皱等。通过识别地震剖面土不整合面和同构造沉积现象,认为构造变形时间在上新世—第四纪;第一排背斜带形成于上新世早期,第二排背斜带发育于上新世中-晚期,第三排背斜带在更新世早-中期开始活动,现今构造形态最终形成于更新世晚期。控制构造变形的主导因素是边界受力方式和非能干性软弱层的纵横向变化。前者决定分段性特征,后者起垂向分层作用,古近系膏泥岩分布范围决定了褶皱变形范围,厚度变化导致浅层变形的强弱。

The structural deformation belt is between south-western margin of Tarim Basin and west Kunlun Mountain,its structural trend is NNW or nearly EW, and with the characteristics of zonation from the south to the north, segmentation from the west to the east, and layering from the deep to the shallow. Basement involved thrust and decollement structure distributed in every segment, belt and layer. The structural styles including break-thrust folds, fault-propagation folds,detachment folds and fold-bend folds. After identifying the unconformity plane and syn- tectonic deposition evidence,it considered that structures were formed mainly in the Pliocene- Quaternary. The northern fold belt was formed in the Early Pliocene, the center fold belt was formed in Middle-Latter Pliocene, and the northern fold belt was formed in Early-Middle Pleistocene. Finally, the present structure pattern of south-western margin was formed after Latter Pleistocene. The dominate factors of structural deformation include boundary manner of strains and distribution variation of incompetent ductile layers. The boundary manner of strains determines the segmentation character. Gypsum-mudstone layer delaminates in vertical direction, its distribution delimits the extent of fold-thrust deformation, and its thickness results the extent of shallow layers＇ deformation.