石碌群的“W”型的叠加褶皱及大型组构解析

海南岛昌江县石碌是我国著名的富铁（钴、铜）矿区。我们对矿区以大比例尺的专门构造地质填图为基础,从石碌群中筛选出普遍发育的四种构造要素,两类褶皱样式群;结合大量剖面、化探及钻孔资料等的综合分析研究。认为石碌群的基本构造格架,主要是由两期褶皱变形叠加组成的“W”型叠加褶皱。本文重点论述石碌群的基本格架及大型组构解析。一、石碌群的“W”型叠加褶皱“W”型叠加褶皱是指:当先存褶皱为轴面陡倾的紧闭线性褶皱,受到后期与其轴向

W-TYPE SUPERPOSED FOLDS IN THE SHILU GROUP AND MACROFABRIC ANALYSIS

Based on the thematic structural mapping on a large scale,four structural elements and two groups of fold style have been sorted out from the Shilu Group.The results of detailed observations,statistical calculations,map preparation and analyses combined with large amounts of data from drill holes and profiles have led to the conclusion that the basic structural framework of the Shilu Group is mainly represented by w-type superposed folds created by deformation and superposion of two phases of folding The macrofabric analysis of the Shilu Group provides the following understandings.（1）The geometric analysis indicates that folds of the two phases making up the w-type structure have the following geometric characteristics: the folds of the first phase are cylindrical and those of the second phase are conical,while macro-axis uplifts（quasi-cylindrical folds）were formed in the inner arcs（cores） of the w-type superposed folds.（2）The kinematic analysis gives a kinematic trajectory of the fabric elements and reveals that the original extension orientation of the first-phase fold axes is roughly NNE.The symmetry analysis shows that the kinemetric plot and mean strain of the first-and second—phase folds are both characterized by monoclinic symmetry,but the symmetric plane of the first-phase folds is the a’c’plane,while that of the second-phase folds,the a"b" plane（the axial plane of the second phase folds）.There exist internal rotational components in the mean strain of the folds of the two phases.（3）The results of kinetic analysis shows that the principal compressive stress generating the first-phase folds is oriented NWW-SEE and exhibits to some extent the behaviour of simple shear and that the orientation of the principal compressive stress of the second fold phase is NNE-SSW.To sum up,a basic picture of the formation and evolution of w-type superposed folds is presented in the paper in the geometric,kinemetric and dynamie respects.