火山岩层原始构造节理研究的一种数学分析方法及其应用

根据原始构造节理系统中节理间特殊的几何关系,本文提出一种数学分析方法及其电算程序,对其进行了研究。宁芜地区一些古火山构造用该法解析成功的实例,证明此种方法是可行的。

A MATH-ANALYTICAL METHOD AND ITS APPLICATIONS FOR THE RESEARCH OF PRIMITIVE TECTONIC JOINTS IN THE VOLCANIC STRATA

In terra of definition the primitive tectonic joints are a set of the earliest crack structures which were formed approximately in the same time and space of rock strata. Generally they include early stage planar × type joints and late stage bedding joints. Many field observations have proved that the geometric relations (as dihedral angles) of these two joints in system of primitive tectonic joints ore particular, which can be used to distinguish them from other. According to Table 1 two obvious characteristics in positive solutions are:1. Intersecting line of conjugate couple (×X-type) is approximately perpendicular to the other part (bedding joint). For practical purposes we screen them out from angles of > = 77.2. The conjugate angles are the least.In fact, the characteristics mentioned above are in essence statistical, so any primitive tectonic joints, screened out from characteristics as above must be rechecked against the conditions of geological setting and then decided which to use.Obviously, the core of studying primitive tectonic joints is to look for the bedding joints (approximately parallel to the bedding of rock strata) from a lot of joints measured in the field. It is a very useful method for rock strata, in which the bedding marks are unknown, especially in the volcanic region. According to the constant geometric relations between the bedding and primitive tectonic joints through a space change calculation, the original structures and ancient stress field for rock strata mentioned above can be restored. This is another use of it. A series of computer calculation program, including 4 segments numbered A. B. C. D, are listed in Table 2, which can be easily used for studying primitive tectonic joints. Their functions are: A calculates dihedral angles for each two joints and arranging the results in matrix form, from which +he primitive tectoric joints can be screened out by two characteristics as said before. B calculates dip and dip-angles for the intersecting line of conjugate couple (corresponding with axis of σ2 in strain analysis) in system of primitive tectonic joints. C calculates the synchronously adjusted dip and dip-angle for rock strata and flow structures, when we rotate the axis of σ2 to vertical position. D calculates angles of azimuth of σ1 and coniugate angles for ancient stress field formed during late period of rock formation.Some successful examples using the math-anglytical method for studying primitive tectonic joints have been described in the 2nd pat of this paper including two main contents:1. determination and restoration of ancient volcanic structures. In this respect, see Fig. 4-7 and their explainations.2. restoration of ancient stress field during the late period of rock formation. Fig. 8 made using segment D has rationally explained the space relations in distribution of famous "Porphyrite Iron Ore Deposits" and Dawangshan formation and origin of a structural breach in the volcanic basement.