Economic and Environmental Geology (자원환경지질)

The Korean Society of Economic and Environmental Geology (대한자원환경지질학회)
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Reactivated Timings of Yangsan Fault in the Northern Pohang Area, Korea

포항 북부지역 양산단층의 재활동 연대

  • Sim, Ho (Department of Earth System Sciences, Yonsei University) ;
  • Song, Yungoo (Department of Earth System Sciences, Yonsei University) ;
  • Son, Moon (Department of Geological Sciences, Pusan National University) ;
  • Park, Changyun (Department of Earth System Sciences, Yonsei University) ;
  • Choi, Woohyun (Department of Earth System Sciences, Yonsei University) ;
  • Khulganakhuu, Chuluunbaatar (Department of Earth System Sciences, Yonsei University)
  • 심호 (연세대학교 지구시스템과학과) ;
  • 송윤구 (연세대학교 지구시스템과학과) ;
  • 손문 (부산대학교 지질환경과학과) ;
  • 박창윤 (연세대학교 지구시스템과학과) ;
  • 최우현 (연세대학교 지구시스템과학과) ;
  • Received : 2017.04.17
  • Accepted : 2017.04.27
  • Published : 2017.04.28
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Abstract

Here we present the timings of reactivated events from a fault in the northern Pohang area, which should be located at the northern-end of Yangsan fault line, the major fault in the southeastern Korean Peninsula. Recently developed illite-age-analysis (IAA) approach was employed for determining the fault-activated timing, combined with illite-polytype quantification using the optimized full-pattern-fitting (FPF) method, and K-Ar age-dating for each size fraction($<0.1{\mu}m$, $0.1-0.4{\mu}m$, and $0.4-1.0{\mu}m$) of 4 fault clay samples. Two chronological records of brittle fault-activation events were recognized at $19.6{\pm}1.86Ma$ and $26.1{\pm}2.55-27.9{\pm}3.46Ma$. The ages are much younger than those of fault clays from Sangcheon-ri area (41.5~43.5 and 50.7 Ma), the southern part of Yangsan fault line, and are close to the timing of East Sea-opening event. Further chronological analysis for additional sites of the Yangsan fault should be needed to reveal the time-scheme of the tectonic events and their spatial distributions along the fault line.

본 연구에서는 한반도 남동부지역 주요단층인 양산단층대 주단층의 북단인 포항북부지역에 나타나는 단층으로부터 결정된 복수의 단층활동연대를 제시하였다. 4개 단층점토별 3개 입도분리 시료($<0.1{\mu}m$, $0.1-0.4{\mu}m$, $0.4-1.0{\mu}m$)에 대해서 일라이트 폴리타입 정량분석 결과 및 K-Ar 연대측정 결과를 일라이트 혼합연대해석법(IAA) 적용 및 해석을 통해 단층활동 절대연대를 결정하였다. 연대해석 결과, $19.6{\pm}1.86Ma$와 $26.1{\pm}2.55{\sim}27.9{\pm}3.46Ma$ 시기의 두 번의 뚜렷한 천부 단층활동연대가 결정되었다. 이 연대는 양산단층대 남부지역인 상천리 일대에서 결정된 단층활동연대(41.5~43.5 및 50.7 Ma) 보다 훨씬 젊은 연대이며, 동해확장과 관련된 지구조운동시기와 매우 근접한 연대이다. 양산단층대에 대한 동일한 방법의 단층활동연대 연구가 이루어질 경우 양산단층대 형성 및 진화와 관련된 지구조운동 시간대와 각 시간대의 공간적 분포 특성 등이 규명될 수 있을 것이다.

Keywords

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