Economic and Environmental Geology (자원환경지질)

The Korean Society of Economic and Environmental Geology (대한자원환경지질학회)
권호 표지
DOI QR코드

DOI QR Code

Mineral Composition and Grain Size Distribution of Fault Rock from Yangbuk-myeon, Gyeongju City, Korea

경주시 양북면 단층암의 광물 조성과 입도 분포 특징

  • 송수정 (경북대학교 지질학과) ;
  • 추창오 (경북대학교 지질학과) ;
  • 장천중 (한국수력원자력(주) 중앙연구원 부지재해평가팀) ;
  • 장태우 (경북대학교 지질학과) ;
  • 장윤득 (경북대학교 지질학과)
  • Received : 2012.03.14
  • Accepted : 2012.10.02
  • Published : 2012.10.28
Download PDF
⟨ Previous Next ⟩

Abstract

This paper is focused on mineral compositions, microstructures and distributional characters of remained grains in the fault rocks collected from a fault developed in Yongdang-ri, Yangbuk-myeon, Gyeongju City, Korea, using X-ray diffraction (XRD), optical microscope, laser grain size analysis and fractal dimension analysis methods. The exposed fault core zone is about 1.5 meter thick. On the average, the breccia zone is 1.2 meter and the gouge zone is 20cm thick, respectively. XRD results show that the breccia zone consists predominantly of rock-forming minerals including quartz and feldspar, but the gouge zone consists of abundant clay minerals such as chlorite, illite and kaolinite. Mineral vein, pyrite and altered minerals commonly observed in the fault rock support evidence of fault activity associated with hydrothermal alteration. Fractal dimensions based on box counting, image analysis and laser particle analysis suggest that mineral grains in the fault rock underwent fracturing process as well as abrasion that gave rise to diminution of grains during the fault activity. Fractal dimensions(D-values) calculated by three methods gradually increase from the breccia zone to the gouge zone which has commonly high D-values. There are no noticeable changes in D-values in the gouge zone with trend being constant. It means that the bulk-crushing process of mineral grains in the breccia zone was predominant, whereas abrasion of mineral grains in the gouge zone took place by continuous fault activity. It means that the bulk-crushing process of mineral grains in the breccia zone was predominant, whereas abrasion of mineral grains in the gouge zone took place by continuous fault activity. Mineral compositions in the fault zone and peculiar trends in grain distribution indicate that multiple fault activity had a considerable influence on the evolution of fault zones, together with hydrothermal alteration. Meanwhile, fractal dimension values(D) in the fault rock should be used with caution because there is possibility that different values are unexpectedly obtained depending on the measurement methods available even in the same sample.

경주시 양북면 용당리에 발달한 단층암을 대상으로 X선 회절 분석(XRD), 광학현미경 분석, 레이저 입도 분석, 프랙탈 차원 분석을 적용하여 단층암의 광물 조성과 미구조, 잔류입자의 분포 특성을 연구하였다. 단층핵은 약 1.5 m 두께로 발달하며 이 중 각력대는 약 1.2m, 단층핵의 가장 중심부인 비지대는 평균 20cm의 얇은 두께로 노출되어 있다. 각력대에서는 석영, 장석류 등의 조암광물이 주 구성 광물로서 산출되고 비지대에서는 녹니석, 일라이트 등의 점토광물이 주 구성 광물로서 산출된다. 단층암에서 빈번하게 산출되는 맥상광물, 황철석, 변질 광물 등은 단층활동과 더불어 열수변질 작용이 수반되었음을 시사하고 있다. 현미경에 의한 구획 점셈(box counting), Image J에 의한 영상분석 및 레이저 입도 분석에 기초한 프랙탈 차원값은 단층암의 입자 파쇄 특성을 잘 보여준다. 세 가지 방법으로 구한 프랙탈 차원값(D)은 각력대에서 비지대로 갈수록 그 값이 증가하고 비지대 내에서는 공통적으로 높은 차원값을 갖는다. 비지대 내에서는 D값의 변화가 상대적으로 적으며, 일정한 경향성이 나타나지 않는다. 이는 각력대에서는 입자들의 대량파쇄가 우세하게 발생하고, 단층운동이 계속되어 생성된 비지대에서는 입자의 마모가 보다 우세하게 발생하였음을 시사한다. 연구지역 단층암의 광물 조성과 입자 분포 특성은 다중 단층 운동과 열수변질 작용이 본 연구지역 단층대의 진화에 큰 영향을 끼쳤음을 지시한다. 단층암에서의 프랙탈 차원값이 측정 기법에 따라 차이가 발생하므로 프랙탈 차원값의 상대적인 비교는 보다 신중히 이용되어야 될 것으로 생각된다.

Keywords

References

  1. Billi, A. (2005) Grain size distribution and thickness of breccia and gouge zones from thin(<1m) strike-slip fault cores in limestone. J. Struct. Geol., v.27, p.1823- 1837. https://doi.org/10.1016/j.jsg.2005.05.013
  2. Blenkinsop, T.G. (1991) Cataclasis and processes of particle size reduction. Pure Appl. Geophys., v.136, p.59-86. https://doi.org/10.1007/BF00878888
  3. Chang, T.W. (2001) Quaternary Tectonic Activity at the Eastern Block of the Ulsan Fault. J. Geol. Soc. Korea., v.37, p.431-444.
  4. Chang, T.W. (2010) Fractals and Fragmentation of Survivor Grains within Gouge Zones along Boundary Faults in the Tertiary Waeup Basin. J. Eng. Geol., v.20, p.183-189.
  5. Chang, T.W. and Chae, Y.J. (2004) Faulting and Hydrothermal Activity in the Gouge Zones of Quaternary Faults at the Eastern Block of the Ulsan Fault. J. Geol. Soc. Korea., v.40, p.469-479.
  6. Chang, T.W., Chae, Y.J. and Choo, C.O. (2005a) Formation of Alteration Minerals in Gouges of Quaternary Faults at the Eastern Blocks of the Ulsan Fault, Southeastern Korea. J. Miner. Soc. Korea., v.18, p.205-214.
  7. Chang, T.W., Chae, Y.J. and Choo, C.O. (2005b) Estimation of Volume Change and Fluid-Rock Ratio of Gouges in Quaternary Faults, the Eastern Blocks of the Ulsan Fault, Korea. J. Eng. Geol., v.15, p.349-363.
  8. Chang, T.W. and Choo, C.O. (1998) Formation Processes of Fault Gouges and their K-Ar Ages along the Dongnae Fault. J. Eng. Geol., v.8, p.175-188.
  9. Chang, T.W. and Choo, C.O. (1999) Faulting Process and K-Ar Ages of Fault Gouges in the Yangsan Fault Zone. J. Korean Earth Sci. Soc., v.20, p.25-37.
  10. Chang, T.W. and Jang, Y.D. (2008) The Widening of Fault Gouge Zone: An Example from Yangbuk-myeon, Gyeongju city, Korea. J. Eng. Geol., v.18, p.135-143.
  11. Choi, P.Y. (2005) Geometri Analysis of the Quaternary Eupchon Fault: an Interpretation of Trench Sections. J. Geol. Soc. Korea., v.41, p.129-140.
  12. Goddard, J.V. and Evans, J.P. (1995) Chemical changes and fluid-rock interaction in faults of crystalline thrust sheets, northwestern Wyoming, U.S.A. J. Struct. Geol., v.17, p.533-547. https://doi.org/10.1016/0191-8141(94)00068-B
  13. Janssen, C., Laube, N., Bau, M. and Gray, D.R. (1998) Fluid regime in faulting deformation of the Waratah Fault Zone, Australia, as inferred from major and minor element analyses and stable isotopic signatures. Tectonophysics., v.294, p.109-130. https://doi.org/10.1016/S0040-1951(98)00127-9
  14. Kee, W.S., Kim, B.C., Hwang, J.H., Song, K.Y. and Kihm, Y.H. (2007) Structural Characteristics of Quaternary reverse faulting on the Eupcheon Fault, SE Korea. J. Geol. Soc. Korea., v.43, p.311-333
  15. Keulen, N., Heilbronner, R., Stunitz, H., Boullier, A.-M. and Ito, H. (2007) Grain size distributions of fault rocks: A comparison between experimentally and naturally deformed granitoids. J. Struct. Geol., v.29, p.1282-1300. https://doi.org/10.1016/j.jsg.2007.04.003
  16. Kim, G.Y., Koh, Y.K., Choi, B.Y., Shin, S.H. and Kim, D.H. (2008) Geochemical Characteristics of the Gyeongju LILW Repository. Rock and Mineral. J. Korean Radioactive Waste Soc., v.6, p.307-324.
  17. Kim, H.J. and Chang, T.W. (2009) Fracture Characteristics and Segmentation of Yangsan Fault around Mt. Namsan, Gyeingju City, Korea. J. Eng. Geol., v.19, p.51-61.
  18. Kim, Y.S. and Jin, K.M. (2006) Estimated earthquake magnitude from the Yugye Fault displacement on a trench section in Pohang, SE Korea. J. Geol. Soc. Korea., v.42, p.79-94.
  19. Kyung, J.B. (2010) Paleoseismological Study and Evaluation of Maximum Earthquake Magnitude along the Yangsan and Ulsan Fault Zones in the Southeastern Part of Korea. Jigu-Mulli-Wa-Mulli-Tamsa., v.13, p.187- 197
  20. Rawling, G. and Goodwin, L.B. (2003) Cataclasis and particulate flow in faulted, poorly lithified sediments. J. Struct. Geol., v.25, p.317-331. https://doi.org/10.1016/S0191-8141(02)00041-X
  21. Ryoo, C.R. (2009) A report for the Quaternary Gaegok 6 Fault Developed in the Mid-eastern Part of Ulsan Fault Zone, Korea. Econ. Environ. Geol., v.42, p.635- 643.
  22. Ryoo, C.R., Lee, B.J., Son, M., Lee, Y.H., Choi, S.J. and Chwae, U.C. (2002) Quaternary faults in Gaegok-ri, Oedong-eup, Gyeongju, Korea. J. Geol. Soc. Korea., v.38, p.309-323.
  23. Shon, S.W., Chang, T.W. and Kim, Y.K. (2002) Mineralogy and Geochemistry of Quaternary Fault Gouges in the Southeastern Korean Peninsula. J. Miner. Soc. Korea., v.15, p.85-94.
  24. Sibson, R.H. (1987) Earthquake rupturing as a mineralizing agent in hydrothermal system. Geology., v.15, p.701-704. https://doi.org/10.1130/0091-7613(1987)15<701:ERAAMA>2.0.CO;2
  25. Sibson, R.H., Moore, J.M. and Rankin, A.H. (1975) Seismic pumping a hydrothermal fluid transport mechanism. J. Geol. Soc. Am., v.131, p.653-659. https://doi.org/10.1144/gsjgs.131.6.0653
  26. Storti, F., Billi, A. and Salvini, F. (2003) Particle size distributions in natural carbonate fault rocks : insights for non-self-similar cataclasis. Earth Planet. Sci. Lett., v.206, p.173-186. https://doi.org/10.1016/S0012-821X(02)01077-4
  27. Wibberley, C. (1999) Are feldspar-to-mica reactions necessarily reaction-softening processes in fault zones?. J. Struct. Geol., v.21, p.1219-1227. https://doi.org/10.1016/S0191-8141(99)00019-X

Cited by

  1. A microstructural study of the fault gouge in the granite, Yangbuk, Gyeongju, southeastern Korea, with implications for multiple faulting vol.21, pp.1, 2017, https://doi.org/10.1007/s12303-016-0021-1
  2. A Study on Mineralogical and Basic Mechanical Properties of Fault Gouges in 16 Faults, Korea vol.28, pp.2, 2015, https://doi.org/10.9727/jmsk.2015.28.2.109
  3. Chemical Behaviors of Elements and Mineral Compositions in Fault Rocks from Yangbuk-myeon, Gyeongju City, Korea vol.22, pp.2, 2013, https://doi.org/10.7854/JPSK.2013.22.2.137