大巴山西北缘叠加褶皱研究

大巴山晚侏罗纪叠加褶皱可能是世界上区域规模或填图规模最典型的褶皱叠加构造之一，具有完美的干涉图像。作者在两期褶皱近乎正交的大巴山西北缘开展1/万填图和构造分析，重点研究露头尺度上的横跨褶皱的几何学、运动学特征。厘定了晚三叠世和晚侏罗世两期构造运动及其两期褶皱变形，确定地壳浅层发育的纵弯褶皱机制，在三维几何形态研究基础上，特别是根据同褶皱层间滑动线理的几何学和运动学及其相互配置关系，基于叠加褶皱力学作用方式和变形干涉图像将区内叠加褶皱划分为3类10种基本样式。研究表明晚侏罗世近南北-北北西向褶皱（F2）近垂直地跨过晚三叠世近东西-北东向褶皱（F1），是大巴山地区最主要的定型构造，构成大巴山晚侏罗纪弧形前陆褶皱山系主体；而北西向褶皱（F3）与近南北-北北西向褶皱（F2）在其中-西部以小的角度相交，总体具非共轴的旋转应变特征，并主要表现为并置或重褶作用。

Superposed buckle folding in the northwest Dabashan, central China

Late Jurassic Superposed folds developed in the foreland structural belt of Mts Dabashan are one of the most typical examples of regional or map-scale buckle superposition structures in the world, characterized by very conspicuous and spectacular interference pattern. A 1:10000 geological mapping was conducted in the northwestern Dabashan where the interference between two almost intersecting folds occurs, aiming at detailed geometric and kinematic analysis of the varied inventory of outcrop-scale cross-folds. The structural analysis indicates that the two discrete folding phases, respectively, related to late middle Triassic and late Jurassic isolated tectonic events are mainly responsible for shallow buckle folds in the study area. In light of the the detailed geometric and kinematic analysis of the various folds and their corresponding dissimilar lineation patterns, three types and ten modes of fold superposition have been differentiated according to interference pattern and Mechanisms of superposed folding. The results show that the SN- to NNW-trending folds(F2) orthogonally overprint the early EW-trending ones (F1). The latter ones formed in the late Jurassic and constitute the major structural elements of the Mts Dabashan. And in situation of non-coaxial bulk deformation, in which the NW-trending folds(F3) are superposed to SN-NNW-trending folds(F2) at a small angle to each other in the west- central study area. The superposed deformation mainly causes the juxtaposing and refolding.