경상남도 남해안에 분포하는 수평 주상절리 형성 메커니즘

Abstract

On the southern coast of Gyeongsangnam-do, horizontally developed columnar joints are observed. In this study, the shape of the horizontal columnar joint is analyzed and the formation mechanism is interpreted. The research areas are Solseom Island and Neokdo Island in Goseong-gun, Cheokpo-ro and the coast at the entrance of Yi Sun-sin Park in Tongyoung-city, Gwanpo-ri and Palangpo-port, of Okpo-dong in Geoje-city. As a result of field survey of igneous rocks and analysis of composition minerals and texture using the polarization microscope, the rocks with developed columnar joints are rhyolite in Goseong-gun, andesite in Tongyeong-city, and basalt in Geoje-city. In Solseom Island, Goseong-gun, the width of the dyke is 150cm, the polygon of the columnar joint are not clear, and in the Neokdo Island where the width of the rock vein is more than 10m, 4∼5 angled polygons are clearly developed. However, in both dykes, the thickness of the columnar joint is not constant. On the coast of Cheokpo-ro, Tongyeong-si, where andesite columnar joints are developed, the width of the dyke is about 5m, and the diameter of the column is relatively constant as about 20cm. The andesite dyke in Jeongyang-dong is about 10M in area observed, and 4-5 squares with a diameter of 20-30cm are clearly developed. The columnar joints in Gwanpo-ri and Okpo-dong in Geoje-city have a thickness of more than 30M of the observed dykes, and 5-6 square columnar joints are well developed. The diameter of columnar joints in Geoje-city varies, but the most frequent is about 30 to 60cm. Columnar joints develop horizontally when lava accumulates in the basin and in the dyke form. Columnar joint in this area is a case of development in the dyke. Since the crack in the columnar joint develops in a direction perpendicular to the fault plane, it can be seen that cooling began from the fault plane. Where the width of the dyke is more than tens of meters, the shape, size, and length of the polygon are also fully developed. In places where the width of the dark vein is small, even if the development of the polygon is incomplete or developed, there are many 4 to 5 triangles. In general, the diameter of columnar joints developed in lava flows is small in high-temperature basic rocks and large in low-temperature acidic rocks. However, in this area, the diameter of columnar joints is large in basalt (Geoje area) and rhyolite (Goseong area) is small. The intrusion scale of the dyke is small in the Goseong area and large in the Geoje area. As a result, columnar joints in dyke depend on the size of the intrusion body rather than the chemical composition. This area is famous for fossils of dinosaur footprints and is already used as a tourism resource as an excellent landscape resource. Columnar joints in the dykes observed in this area are included in the learning elements presented in the textbook and are of high value as a geological learning center.