Economic and Environmental Geology (자원환경지질)

The Korean Society of Economic and Environmental Geology (대한자원환경지질학회)
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Preliminary Structural Geometry Interpretation of the Pyeongchang Area in the Northwestern Taebaeksan Zone, Okcheon Belt: A Klippe Model

옥천대 북서부 태백산지역 평창 일대의 클리페 모델 기반 구조기하 형태 해석 예비 연구

  • Heunggi Lee (Department of Earth System Sciences, Yonsei University) ;
  • Yirang Jang (Department of Earth and Environmental Sciences, Chonnam National University) ;
  • Sanghoon Kwon (Department of Earth System Sciences, Yonsei University)
  • 이흥기 (연세대학교 이과대학 지구시스템과학과) ;
  • 장이랑 (전남대학교 자연과학대학 지구환경과학부 지질환경전공) ;
  • 권상훈 (연세대학교 이과대학 지구시스템과학과)
  • Received : 2023.12.15
  • Accepted : 2023.12.21
  • Published : 2023.12.29
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Abstract

The Jucheon-Pyeongchang area in the northwestern Taebaeksan Zone of the Okcheon fold-thrust belt preserved several thrust faults placing the Precambrian basement granite gneisses of the Gyeonggi Massif on top of the Early Paleozoic Joseon Supergroup and the age-unknown Bangrim Group. Especially, the thrust faults in the study area show the closed-loop patterns on the map view, showing older allochthonous strata surrounded by younger autochthonous or para-autochthonous strata. These basement-involved thrusts including Klippes will provide important information on the hinterland portion of the fold-thrust belt. For defining Klippe geometry in the thrust fault terrains of the Jucheon-Pyeongchang area by older on younger relationship, the stratigraphic position of the age-unknown Bangrim Group should be determined. The Middle Cambrian maximum depositional age by the detrital zircon SHRIMP U-Pb method from this study, together with field relations and previous research results suggest that the Bangrim Group overlies the Precambrian basement rocks by nonconformity and underlies the Cambrian Yangdeok Group (Jangsan and Myobong formations). The structural geometric interpretation of the Pyeongchang area based on newly defined stratigraphy indicates that the Wungyori and Barngrim thrusts are the same folded thrust, and can be interpreted as a Klippe, having Precambrian hanging wall granite gneisses surrounded by younger Cambrian strata of the Joseon Supergroup and the Bangrim Group. Further detailed structural studies on the Jucheon-Pyeongchang area can give crucial insights into the basement-involved deformation during the structural evolution of the Okcheon Belt.

한반도의 대표적인 습곡-단층대 중 하나인 옥천대의 주천-평창지역에는 경기육괴 기반암을 고생대 조선누층군 및 시대미상의 방림층군 상위로 충상시키는 다수의 트러스트 단층이 발달한다. 이 지역의 트러스트들은 상반의 암체가 하반의 암체로 완전히 둘러싸인 폐곡선 형태의 독특한 자취를 보이며, 이는 전형적인 클리페의 지질도 상 특징으로 해석될 수 있다. 특히, 연구 지역과 같이 트러스트 상반에 기반암을 포함하는 클리페의 경우에는 습곡-단층대 배후지의 구조 발달을 이해하는데 중요하다. 그러나 클리페 구조가 잘 정의되기 위해서는 층서적으로 오래된 암체가 트러스트를 경계로 상대적으로 젊은 암체의 상위에 구조적으로 완전히 고립된 형태를 보여야 하기 때문에, 연구지역에 넓게 분포하는 시대미상 방림층군의 지질연대가 매우 중요하다. 본 연구에서는 SHRIMP U-Pb 저어콘 연대측정을 통해 획득한 방림층군의 최대 퇴적시기와 야외조사 결과 및 기존 연구를 종합하여, 방림층군을 아래로는 선캄브리아시대 화강편마암과 위로는 전기 고생대 조선누층군 양덕층군(장산층, 묘봉층)의 지층 사이에 놓이는 고생대 캄브리아기 최하부 지층에 대비하였다. 이를 바탕으로 평창지역에 대한 구조기하 형태 연구를 수행한 결과, 운교리트러스트와 방림트러스트는 하나의 습곡된 트러스트이며 운교리트러스트 상반의 암체들이 하반 암체들에 의해 완전히 고립된 특징을 보이는 클리페 모델로 해석이 가능함을 확인하였다. 향후 주천-평창지역에 대한 구조지질학적 측면의 후속 연구들을 통해 클리페 모델에 대한 추가적인 테스트가 이루어진다면, 옥천대의 구조 진화에 있어서 기반암을 포함하는 변형 기작의 역할에 대해 중요한 정보를 획득할 수 있을 것이다.

Keywords

Acknowledgement

본 논문은 이흥기의 연세대학교 석사학위 연구내용의 일부를 포함하고 있습니다. 추가 연구수행 및 원고의 작성은 한국연구재단 우수신진연구과제(2021R1C1C101057011)의 지원으로 책임저자에 의해 수행되었습니다. 또한 한국연구재단 중점연구소 과제(2017R1A6A1A07015374) 및 중견연구과제(2019R1A2C1002211)와 원자력환경공단 과제(2021040101003B)의 일부 지원에 의해 수행되었습니다. 시료 취득에 도움을 주신 한국지질자원연구원 진광민 박사님을 비롯하여, 본 논문을 심사해 주신 두 분의 심사위원과 책임편집위원, 편집위원장께 감사드립니다.

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