경상남도 고성군 서남부에 분포하는 구조절리와 중첩된 주상절리의 형태 분석 방법

Abstract

In the study area, clastic sedimentary rocks and volcanic rocks distributed in the Mesozoic era are analyzed. Columnar joints are developed in volcanic rocks, but structural joints formed by diastrophism that occurred after the Mesozoic Era also developed together, making it difficult to understand the shape. This study analyzed the strikes of structural joints in sedimentary rocks that are not related to columnar joints. Also, by removing the influence of structural joints in the area developed together with columnar joints, we an attempt to clearly interpret the characteristics of columnar joints will be undertaken. Among the sedimentary rocks of the study area, five sites with distinctly developed joints were selected and the strike of the joints was measured. In the site 1(Maekjeonpohang area), the direction of N70°W~EW is the most dominant for the strike of joints. Next, N30°~50°E and N20°~40°W show similar frequencies. In the site 2 (Yongampohang area), joints in the NS direction are overwhelmingly dominant, and in the site 3 (Anjang Island and Tokki Island), joints in the EW direction are most dominant. In the site 4 (Donghwa-ri), joints in the EW direction are dominant, but joints in the N20°~30°W and N10°~30°E directions also develop. In the site 5 (Yuk Island and Neuk Island), joints in the EW direction are dominant, and joints in the NNS or NNE directions are weakly developed. Therefore, in the sedimentary rocks of the study area, joints are developed in three directions. Among them, the EW series is the most dominant and develops in the order of N30°E, N30°W. By applying the results described above to volcanic rocks overlapping columnar joints and structural joints, the characteristics of columnar joints were analyzed after removing the effect of structural joints. As a result, the proportion of hexagonal columnar joints developed in the volcanic rocks of the study area was 41.6% in the site 1, 50% in the site 2, and 48.1% in the site 3 and 5. In the site 4, however, does not have volcanic rocks with columnar joints developed. In the southern coast, not only volcanic rocks, but also sedimentary rocks and granites, joints develop almost vertically due to diastrophism. These structural joints are often mistakenly called columnar joints because they are similar to the shape of columnar joints formed by the cooling and contraction of volcanic rocks. There is also a possibility that the researcher incorrectly describes the polygon of the columnar joints with overlapping structural joints. Therefore, when describing polygons of columnar joints developed along the southern coast, the influence of structural joints must be removed. This study can clearly present the concepts of structural joints(or vertical joints) and columnar joints, which are often confused by the general public. In addition, it will provide clear guidelines for describing the polygons of columnar joints to researchers who describe columnar joints.