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Collapse Type and Processes of the Geumosan Caldera in the Southern Gumi, Korea
구미 남부 금오산 칼데라의 함몰 유형과 과정
Econ. Environ. Geol. 2021 Feb;54(1):35-48
Published online February 28, 2021;  https://doi.org/10.9719/EEG.2021.54.1.35
Copyright © 2021 the Korean society of economic and environmental gelology.

Sang Koo Hwang1, Young Woo Son2, Seung Hwan Seo3, Weon-Seo Kee4,*
황상구1 · 손영우2 · 서승환3 · 기원서4,*

1Department of Earth and Environmental Sciences, Andong National University, Andong 36729, Korea
2Korea Water Resources Corporation, Daejeon 34350, Korea
3Mungyeong City Gyeongsangbuk Province, Mungyeong 36982, Korea
4Korea Institute of Korea Institute of Geoscience and Mineral Resources, Daejeon 34132, Korea
1안동대학교 자연과학대학 지구환경과학과 2한국수자원공사 보현산댐지사 3경상북도 문경시청 환경보호과 4한국지질자원연구원 국토지질연구부
Received December 1, 2020; Revised January 14, 2021; Accepted January 18, 2021.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
 Abstract
The Gumi basin, situated in the mid-southeastern Yeongnam Massif, has the Cretaceous stratigraphy that is divided into Gumi Formation, andesitic rocks (Yeongamsan Tuff, Busangni Andesite), rhyolitic rocks (Obongni Tuff, Doseongul Rhyolite, Geumosan Tuff) and Intrusives (ring dikes, other dikes) in ascending order. The Geumosan Tuff is composed mostly of many ash-flow tuffs which are associated with Geumosan caldera along with the ring dikes. The caldera is outlined by ring faults and dikes and has about 3.5 × 5.6 km in diameters. The intracaldera volcanics show a downsag structure that is dipped inward in their flow and welding foliations. The caldera block represent an asymmetric subsidence, which drops 350 m in the northern margin and 600 m in the southern one. Based on these data, the Geumosan caldera is geometrically classified as an asymmetric piston subsidence caldera that suggests a single caldera cycle. The caldera reflects the piston subsidence of the caldera block bounded by the outward-dipping ring faults following a voluminous eruption of magma from the chamber. The downsag in the caldera block refers to the downsagging during the initial subsidence at the same time as the full development of the bound fault. In the ring fissures following the sagging, magma was injected due to the overpressure of magma chamber caused by subsidence.
Keywords : Geumosan caldera, ash-flow tuff, ring dike, piston subsidence, downsagging

 

February 2021, 54 (1)