The Journal of the Petrological Society of Korea (암석학회지)

The Petrological Society of Korea (한국암석학회)
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Geometric and Kinematic Characteristics of Fracture System in the Sancheong Anorthosite Complex, Korea

산청 회장암복합체 내 발달하는 단열계의 기하학적·운동학적 특성

  • Lee, Deok-Seon (Department of Earth and Environmental Sciences, Andong National University) ;
  • Kang, Ji-Hoon (Department of Earth and Environmental Sciences, Andong National University)
  • 이덕선 (안동대학교 지구환경과학과) ;
  • 강지훈 (안동대학교 지구환경과학과)
  • Received : 2016.12.09
  • Accepted : 2016.12.23
  • Published : 2016.12.31
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Abstract

The study area, which is located in the southeastern part of the Jirisan province of the Yeongnam massif, Korea, consists mainly of the Precambrian Sancheong anorthosite complex and the Jirisan metamorphic rock complex, the Mesozoic granitoids which intruded them. Several fracture sets with various geometric indicators, which determine their relative timing and shear sense, are well observed in the Sancheong anorthosite complex. The aim of this study is to determine the development sequence of extension fractures, the movement sense and development sequence of shear fractures in the Sancheong anorthosite complex on the basis of detailed analysis of their geometric indicators. This study suggests fracture system of the Sancheong anorthosite complex was formed at least through five different fracturing events, named as Dn to Post-Dn+3 phases. (1) Dn phase: extension fracturing event of NNW trend. The fracture set experienced the reactivations of dextral ${\rightarrow}$ sinistral shearing with the change of stress field afterward. (2) Dn+1 phase: extension fracturing event of (N)NE trend. The fracture set experienced the reactivations of sinistral ${\rightarrow}$ sinistral ${\rightarrow}$ dextral. (3) Dn+2 phase: extension fracturing event of NW trend. The fracture set experienced the activated of dextral shearing. (4) Dn+3 phase: extension fracturing event of N-S trend. (5) Post-Dn+3 phase: extension fracturing event of (E)NE trend. Dn deformation formed during the early Songnim orogeny. Dn+1 deformation formed during the late Songnim orogeny. Dn+2 deformation formed during the Daebo orogeny. Dn+3 deformation formed during the Bulguksa orogeny.

영남육괴 지리산지구의 남동부에 위치하는 산청지역은 주로 선캄브리아시대 지리산 변성암복합체, 산청 회장암복합체, 중생대 화성암류 등으로 구성되어 있다. 산청 회장암복합체 내에는 다수의 단열조의 상대적인 시간관계(선후관계 및 공존관계)와 전단단열의 발달순서 및 운동감각을 결정하는데 이용되는 기하학적 지시자가 잘 관찰된다. 본 논문은 이들 다수의 단열조에 대한 방향성과 운동학적 기하학적 특성을 정밀하게 분석하여 산청 회장암복합체에 발달하는 인장단열의 발달순서와 전단단열의 발달순서 및 운동성을 고찰하였다. 그 결과 산청 회장암복합체에 발달하는 단열계는 적어도 5회의 변형단계(Dn 단계에서 Dn+3 이후단계로 명기)를 걸쳐 형성되었음이 인지된다. (1) Dn 단계: 북북서-남남동 방향의 인장단열 형성기. 이후 응력장 변화로 인해 우수향 ${\rightarrow}$ 좌수향 전단단열운동을 활동하였다. (2) Dn+1 단계: (북)북동-(남)남서 방향의 인장단열 형성기. 이 단계의 단열조는 이후 좌수향 ${\rightarrow}$ 좌수향 ${\rightarrow}$ 우수향 전단단열운동으로 재활동하였다. (3) Dn+2 단계: 북서-남동 방향의 인장단열 형성기. 이후, 우수향 전단단열운동을 겪었다. (4) Dn+3 단계: 남-북 방향의 인장단열 형성기. (5) Dn+3 이후단계: (동)북동-(서)남서 방향의 인장단열 형성기. Dn 단계는 송림조산운동 전기, Dn+1 단계는 송림조산운동 후기, Dn+2 단계는 대보조산운동 시기, Dn+3 단계는 불국사 조산운동 시기 그리고 Dn+3 이후단계는 불국사 조산운동 시기 이후에 형성되었다.

Keywords

References

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