지질공학 (The Journal of Engineering Geology)

  • 제28권4호
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  • Pages.645-660
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  • 2018
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  • 1226-5268(pISSN)
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  • 2287-7169(eISSN)
대한지질공학회 (The Korean Society of Engineering Geology)
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일광단층 동편에서 관찰되는 지질구조를 이용한 고응력사 해석

Interpretation of Paleostress using Geological Structures observed in the Eastern Part of the Ilgwang Fault

  • 김태형 (부경대학교 지구환경과학과 지질구조재해연구실) ;
  • 정수호 (부경대학교 지구환경과학과 지질구조재해연구실) ;
  • 이진현 (부경대학교 지구환경과학과 지질구조재해연구실) ;
  • ;
  • 양원동 (부경대학교 지구환경과학과 지질구조재해연구실) ;
  • 지도형 (부경대학교 지구환경과학과 지질구조재해연구실) ;
  • 김영석 (부경대학교 지구환경과학과 지질구조재해연구실)
  • Kim, Taehyung (Division of Earth Environmental System Science (Major of Earth & Environmental Sciences)) ;
  • Jeong, Su-Ho (Division of Earth Environmental System Science (Major of Earth & Environmental Sciences)) ;
  • Lee, Jinhyun (Division of Earth Environmental System Science (Major of Earth & Environmental Sciences)) ;
  • Naik, Sambit Prasanajit (Division of Earth Environmental System Science (Major of Earth & Environmental Sciences)) ;
  • Yang, Wondong (Division of Earth Environmental System Science (Major of Earth & Environmental Sciences)) ;
  • Ji, Do Hyung (Division of Earth Environmental System Science (Major of Earth & Environmental Sciences)) ;
  • Kim, Young-Seog (Division of Earth Environmental System Science (Major of Earth & Environmental Sciences))
  • 투고 : 2018.11.06
  • 심사 : 2018.12.13
  • 발행 : 2018.12.31
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초록

한반도 동남부에는 양산단층과 울산단층을 비롯한 대규모 단층곡이 인지된다. 이 두 단층을 포함한 북북동-남남서 방향의 단층곡들을 총칭하여 양산단층계라고 한다. 그러나 이 단층계의 중요성에 비해 양산단층과 울산단층을 제외한 다른 단층곡들은 상대적으로 연구가 부진하다. 본 연구는 이 단층계 중에서 가장 동편의 선형구조인 일광단층 주변에 위치한 봉대산과 대변항 일원에서 화강암 내에 발달한 지질구조들의 상호 절단관계를 통해 고응력변화를 추론 하였고, 이를 기존 선행연구와 비교 검토하였다. 연구지역에서는 일광단층과 평행한 선형구조가 4개 인지되며, 그 중 3개의 선형구조에서 단층의 증거를 확인하였다. 각 선형구조를 따른 단층에서는 좌수향 및 우수향의 주향이동 운동감각이 모두 인지되었다. 이는 선형구조를 따라 반전 다중변형을 겪은 것을 지시하는 것으로 판단된다. 지질구조들의 상호절단관계를 통해 분석한 응력방향은 1) 후기 백악기에 동북동-서남서 방향의 압축에 따른 인장단열들이 먼저 발달하고, 2) 북서-남동 방향의 압축에 따른 공액상의 주향이동단층들이 발달하였으며, 3) 북동-남서 방향의 압축에 따라 일부 구조들의 선택적 재활운동이 있었던 것으로 해석된다.

In the southeastern part of the Korean Peninsula, huge fault valleys, including the Yangsan and Ulsan faults, are recognized. These NNE-SSW trending lineaments are called as a whole Yangsan Fault System. However, this fault system is relatively poorly studied except the Yangsan and Ulsan faults. This study deduced the paleostress history based on the mutual cross-cutting relationships between geologic structures developed in the granite body near the Ilgwang fault, which is compared with previous studies. In the study area, four lineaments parallel to the Ilgwang fault are recognized, and three of them show evidences of faulting. In each lineament, both slip-senses of left-lateral and right-lateral are recognized. It indicates that these faults consistently underwent multiple deformations of inversion along the faults. The inferred paleostress directions based on the mutual cross-cutting relationships of the geological structures are as follows: 1) Tensile fractures developed in the late Cretaceous under the ENE-WSW direction of compressive stress, 2) NW-SE trending maximum horizontal principal stress generated conjugate strike-slip faults, and 3) selective reactivations of some structures were derived under the compression by the NE-SW trending principal stress.

키워드

JJGHBG_2018_v28n4_645_f0001.png 이미지

Fig. 1. (a) Main lineaments of the southeastern part of the Korean peninsula. NNE-SSW trending lineament and NNW-SSE trending lineament are recognized on the hillshade image(MYF : Milyang fault, MRF : Moryang fault, YSF : Yangsan fault, DNF : Dongnae fault, IFG : Ilgwang fault, USF : Ulsan fault). (b) Geological map of the study area. The study area is composed of the Cretaceous sedimentary and igneous rocks. The NNE striking Ilgwang fault is marked as a dashed line (modified from Son et al., 1978).

JJGHBG_2018_v28n4_645_f0002.png 이미지

Fig. 2. Geomorphological map of the study area. NE-SW or NNE-SSW trending lineaments are recognized on hillshade image.

JJGHBG_2018_v28n4_645_f0003.png 이미지

Fig. 3. NE-SW striking sinistral strike-slip fault with secondary fractures at L2-b site in Fig. 2.

JJGHBG_2018_v28n4_645_f0004.png 이미지

Fig. 5. (a) L4 fault of the Figure 2. (b) Fault zone combined with different fault rocks such as gouge and breccia. (c&d) WNW-ESE trending quartz veins(yellow triangle) displaced by L4 fault with dextral strike-slip sense. (e&f) WNW-ESE trending quartz veins (yellow triangle) displaced by L4 fault with sinistral strike slip sense.

JJGHBG_2018_v28n4_645_f0005.png 이미지

Fig. 5. (a-f) Examples of cross cutting relationship. ENE-WSW and NW-SE striking veins are displaced by several minor strike-slip faults. (g) Rose diagrams for veins, minor strike-slip faults and related paleostress conditions.

JJGHBG_2018_v28n4_645_f0006.png 이미지

Fig. 6. (a&b) En-echelon fractures and quartz veins along the WNW-ESE to NW-SE trending shear zones. According to their geometry, this shear zone reactivated with opposite slip senses(inversion). (c&d) Detailed photo and sketch to recognize their cross cutting relationship (T.D: Tensile fractures related to dextral movement, T.S: Tensile fractures related to sinistral movement, R.D: Riedel shears related to dextral movement, R'.D: Conjugate Riedel shears related to dextral movement).

JJGHBG_2018_v28n4_645_f0007.png 이미지

Fig. 7. Schematic diagrams for the inversion process. (a) Rotated tensile fractures (vein) related to dextral movement during the sinistral stage. (b) Riedel shears related to dextral movement filled with quartzx vein by transtensional stress (T.D: Tensile fractures related to dextral movement, T.S:Tensile fractures related to sinistral movement, R.D: Riedel shears related to dextral movement, R'. D: Conjugate Riedel shears related to dextrral movement).

JJGHBG_2018_v28n4_645_f0008.png 이미지

Fig. 8. Paleostress history interpretations based on geometrical and kinematical evidences. Each stereographic projection inidicates structural elements in each outcrop. (a-f) ENE-WSW striking quartz veins displaced by several strike-slip faults developed under NW-SE trending maximum horizontal stress. (g) NE-SW striking quartz vein was displaced by NNW-SSE striking sinistral strike-slip fault developed under WNW-ESE trending maximum horizontal stress. (h) NNW-SSE tending quartz veins displaced by the conjugate set of strike-slip fault. (i) WWN-ESE dextral strike-slip faults and NW-SE T fractures developed during the stage 2 and NE-SW T fractures developed during the stage 3. The structures developed during the stage 2 are reactivated during the stage 3 (T.D : Tensile fractures related to dextral movement, T.S: Tensile fractures related to sinistral movement, R'. D: Conjugate Riedel shears related to dextral movement).

Table 1. Estimated paleostress directions based on the interpretation of structural elements form each outcrop

JJGHBG_2018_v28n4_645_t0001.png 이미지

Table 2. Summary of the deformation history around the study area and comparison with previous studies.

JJGHBG_2018_v28n4_645_t0002.png 이미지

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