一种解析正圆锥状褶皱和复杂环带的方法——三点法

圆锥状褶皱是与圆柱状褶皱几何特征不同但又有一定联系的构造,在自然界并不少见,不仅可以出现于圆柱状褶皱的尾端,而且常见于多期构造变形迭加的地区。作者在辽宁省鞍本地区进行变质岩构造解析时,也遇到了多个不同尺度的圆锥状褶皱。

A METHOD TO ANALYSE CIRCULAR CONICAL FOLDS AND COMPLEX GIRDLES——THREE-POINT METHOD

An universally applicable graphic method, the three-point method, is suggested to analyse structural geometry of circular conical folds with central axes appearing in whatever attitude. So long as the measured πS data have been projected onto an equal-area net and a more or less small-circle girdle pattern has presented, it is possible to know if the girdle is a small-circle girdle through a series of operations, to obtain fit small-circle arc for the small-circle girdle, to acquire that fold’s central axis, vertex angle, bisecting surface (axial plane), vertex aris (fold hinge) and β-intersection triangle, without requirement for having known datum of any of the structural elements in advance.The main steps of the three-point method are to determine three datum points on the primary girdle to find the initial small-circle’s center and the initial small circle, to find out fit small circle for original contour girdle, to delimit fit small circle arc, to analyse whole structure and to examine errors.The three-point method has also included the pole method which he useful for constructing β-intersection triangle, it makes the operation easier and faster. Four laws are suggested, which show the geometrical relationship between the small-circle are and its β-intersection trangle.The three-point method is rather simple and convenient and suitable for analysis of small circle girdles of whatever fabric elements.It is possible to find the structural informations and data included in complicated girdles, to understand their symmetries and recognize if some complicated girdle figures are different or identical but with different attitude by separating some complicated girdles inito several parts and analysing every small-circle part with the three-point method.