沃川帶의 地質 및 鑛物資源에 關한 硏究

Geology and Mineral Resources of the Okchŏn Zone-The Boundary between the Okchŏn and Chosŏn Systems in the South of Jechŏn, and the Geology in its Vicinity-

Various interpretations on the boundary between the Okchŏn system and the Great Limestone series of the Chosŏn system, and on the geologic structure and stratigraphy of the Okchŏn system have been yielded by the previous studies, and they are still in hot debate. The present work has mainly studied on the boundary between the Okchŏn and Chosŏn systems in the south of Jechŏn, and the geology in its vicinity to clarify the previous misinterpretations if any on the geologic structure and in trun stratigraphy of the area concerned. The boundary between the Okchŏn system and the Great Limestone series of the Chosŏn system has been thought to be (1) gradational relation which means two systems are the same formation, (2) unconformable relation in which the Okchŏn system overlies the Chosŏn system, (3) unconformable relation in which the Chosŏn system overlies the Okchon system indicating that the age of the Okchŏn system is Precambrian, and (4) fault contact in which the Okchŏn system of Precambrian age comes in contact with the Chosŏn system of Cambro-Ordovician age. The present study clearly found that the relationship between the two systems is a fault zone contact. Shear zone of a width of 300 to 400m is developed, and andesitic volcanics and basic dikes are intruded along the fault zone. This fault contact is exactly the north extension of the Bonghwajae fault, which was denominated long time ago by two of the present authors. The eastern side of the fault has been uplifted so that the Sŏchangri formation of the Okchŏn system cropped out in the zone of the Great Limestone series. All the previous workers thought that the Sŏchangri formation rests on the Great Limestone series, but the present study found an overthrust having a strike of N8°E and dip of 30°NW between them, and the Sŏchangri formation has thrusted over the Great Limestone series at the central part of the study area. In the southern and northern parts of this uplifted Sŏchangri formation, the Great Limestone series rests unconformably on it. In the eastern part of the study area where the Mt. Dangdu is located and the previous workers thought that the Sŏchangri formation rests on the Great Limestone series, Precambrian basement rock whose age is older than 1720+50 m.y. crops out in the northern part of the east-west trending high angle fault, and the Great Limestone series rests unconformably on the basement.