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Structural Geometry, Kinematics and Microstructures of the Imjingang Belt in the Munsan Area, Korea

임진강대 문산지역의 구조기하, 키네마틱스 및 미세구조 연구

  • Lee, Hyunseo (Department of Earth System Sciences, Yonsei University) ;
  • Jang, Yirang (Department of Earth and Environmental Sciences, Chonnam National University) ;
  • Kwon, Sanghoon (Department of Earth System Sciences, Yonsei University)
  • 이현서 (연세대학교 지구시스템과학과) ;
  • 장이랑 (전남대학교 지구환경과학부 지질환경전공) ;
  • 권상훈 (연세대학교 지구시스템과학과)
  • Received : 2021.02.18
  • Accepted : 2021.04.19
  • Published : 2021.04.28

Abstract

The Imjingang Belt in the middle-western Korean Peninsula has tectonically been correlated with the Permo-Triassic Qinling-Dabie-Sulu collisional belt between the North and South China cratons in terms of collisional tectonics. Within the belt, crustal-scale extensional ductile shear zones that were interpreted to be formed during collapsing stage with thrusts and folds were reported as evidence of collisional events by previous studies. In this study, we tried to understand the nature of deformation along the southern boundary of the belt in the Munsan area based on the interpretations of recently conducted structural analyses. To figure out the realistic geometry of the study area, the down-plunge projection was carried out based on the geometric relationships between structural elements from the detailed field investigation. We also conducted kinematic interpretations based on the observed shear sense indicators from the outcrops and the oriented thin-sections made from the mylonite samples. The prominent structures of the Munsan area are the regional-scale ENE-WSW striking thrust and the N-S trending map-scale folds, both in its hanging wall and footwall areas. Shear sense indicators suggest both eastward and westward vergence, showing opposite directions on each limb of the map-scale folds in the Munsan area. In addition, observed deformed microstructures from the biotite gneiss and the metasyenite of the Munsan area suggest that their deformation conditions are corresponding to the typical mid-crustal plastic deformation of the quartzofeldspathic metamorphic rocks. These microstructural results combined with the macro-scale structural interpretations suggest that the shear zones preserved in the Munsan area is mostly related to the development of the N-S trending map-scale folds that might be formed by flexural folding rather than the previously reported E-W trending crustal-scale extensional ductile shear zone by Permo-Triassic collision. These detailed examinations of the structures preserved in the Imjingang Belt can further contribute to solving the tectonic enigma of the Korean collisional orogen.

한반도 중서부에 위치한 임진강대는, 페름기-트라이아스기에 북중국판과 남중국판이 충돌하여 형성된 친링-다비-술루 대륙충돌대와 지구조적으로 대비되고 있는 지역으로, 지각규모의 전단대, 트러스트 및 습곡 등의 충돌조산운동 관련 지질구조들이 보존되어 있는 것으로 알려져 왔다. 본 연구는 경기육괴와 접하는 임진강대의 남쪽 경계지역인 문산지역에서 수행한 구조지질 연구결과를 종합하고, 이를 바탕으로 기존에 이 지역에서 일부 연구자들에 의해 대륙충돌로 형성된 조산대 후기 붕괴 단계에 형성된 것으로 제안되었던 지각규모 신장성 경기전단대의 존재와 변형 특성에 관해 검토하고자 하였다. 이를 위해, 야외조사를 통해 획득한 지질요소 자료를 바탕으로 문산지역의 구조기하학적 형태를 해석하였고, 노두 및 박편 상에서 확인한 전단감각 지시자로부터 암석 이동과 관련된 키네마틱스를 해석하였다. 이 지역의 가장 주된 지질구조는 동북동-서남서 주향의 광역규모 임진강단층의 상반 및 하반에 발달한 대략 남-북 주향의 힌지를 가지는 지질도규모의 습곡이다. 이 습곡에 대한 키네마틱스 해석 결과는 전단감각들이 습곡의 힌지를 중심으로 양쪽 익부에서 서로 반대 방향으로 대략 동쪽 내지 서쪽을 향함을 지시한다. 또한 문산지역 흑운모편마암과 변성섬장암의 광물 미세변형구조 관찰 결과로부터 유추한 암석의 변형조건은 전형적인 석영-장석질 암석들의 중부지각 소성변형조건에 해당한다. 따라서 본 연구를 통해 획득한 문산지역의 구조기하, 키네마틱스 및 미세구조 분석결과는 이 지역에 발달한 전단대가 기존 연구들에서 제안된 대륙충돌 후기에 형성된 지각규모의 신장성 경기전단대보다는, 요굴습곡작용에 의한 지질도규모 습곡의 발달과 관련된 전단운동의 결과일 가능성이 높은 것으로 제안한다. 이와 같은 임진강대 내 대륙충돌의 증거들에 대한 상세한 구조지질학적 검증은 향후 한반도 충돌조산운동에 있어 임진강대의 지구조적 역할에 대한 난제들을 해결하는데 중요한 정보를 제공할 수 있을 것으로 기대된다.

Keywords

References

  1. Behrmann, J.H. and Mainprice, D. (1987) Deformation mechanism in a high temperature quartz-feldspar mylonite: evidence for superplastic flow in the lower continental crust. Tectonophysics, v.140, p.297-305. doi: 10.1016/0040-1951(87)90236-8
  2. Bell, T.H. and Johnson, S.E. (1989) The role of deformation partitioning in the deformation and recrystallization of plagioclase and K-feldspar in the Woodroffe thrust mylonite zone, Central Australia. Journal of Metamorphic Geology, v.7, p.151-168. doi: 10.1111/j.1525-1314.1989.tb00582.x
  3. Chang, K.-H. and Zhao, X. (2012) North and South China suturing in the east end: What happened in Korean Peninsula?. Gondwana Research, v.22, p.493-506. doi: 10.1016/j.gr.2011.12.010
  4. Cho, M., Kwon, S.-T., Ree, J.-H. and Nakamura, E. (1995) High-pressure amphibolite of the Imjingang belt in the Yeoncheon-Cheongok area. The Journal of Petrological Society of Korea, v.4, p.1-19 (in Korean with English abstract).
  5. Cho, M., Kim , Y. and Ahn, J. (2007) Metamorphic evolution of the Imjingang Belt, Korea: implications for Permo-Triassic collisional orogeny. International Geology Review, v.49, p.30-51. doi: 10.2747/0020-6814.49.1.30
  6. Choi, S.-J., Lee, S.R., Kim, K.B., Kim, J.R. and Kim, B.C. (1998) Explanatory text of the Geological map of Munsan sheet (1:50,000). Korea Institute of Geology, Mining and Materials, 79p. (in Korean with English summary)
  7. Chwae, U. and Choi, S.-J. (2009) Stratigraphic and Structural Review of Yeoncheon Group and Imjingang Fold Belt, and Its Edge of Distribution. Economic and Environmental Geology, v.42, p.627-634 (in Korean with English abstract)
  8. Chwae, U., Choi, S.-J., Park, K.H. and Kim, K.B. (1996) Explanatory text of the Geological map of Cheolwon-Majwonri sheet (1:50,000). Korea Institute of Geology, Mining and Materials, 31p. (in Korean with English summary)
  9. Debat, P., Soula, J.C., Kubin, L. and Vidal, J.L. (1978) Optical studies of natural deformation microstructures in feldspars (gneiss and pegmatites from Occitania, Southern France). Lithosphere, v.11, p.133-145. doi: 10.1016/0024-4937(78)90004-x
  10. Ernst, W.G. and Liou, J.G. (1995) Contrasting plate-tectonic styles of the Qinling-Dabie-Sulu and Franciscan metamorphic belts. Geology, v.23, p.353-356. doi: 10.1130/0091-7613(1995)023<0353:cptsot>2.3.co;2
  11. Hanmer, S.K. (1982) Microstructure and geochemistry of plagioclase and microcline in naturally deformed granite. Journal of Structural Geology, v.4, p.197-213. doi: 10.1016/0191-8141(82)90027-X
  12. Hirth, G. and Tullis, J. (1992) Dislocation creep regimes in quartz aggregates. Journal of Structural Geology, v.14, p.145-159. doi: 10.1016/0191-8141(92)90053-Y
  13. Ishiwatari, A. and Tsujimori, T. (2001) Late Paleozoic HighPressure Metamorphic Belts in Japan and Sikhote-Alin. Possible oceanic extension of the Chinese Dabie-Su-Lu Suture detouring Korea. Gondwana Research, v.4, p.636-638. doi: 10.1016/s1342-937x(05)70439-1
  14. Isozaki, Y., Aoki, K., Nakama, T. and Yanai, S. (2010) New insight into a subduction-related orogen: A reappraisal of the geotectonic framework and evolution of the Japanese Islands. Gondwana Research, v.18, p.82-105. doi: 10.1016/j.gr.2010.02.015
  15. Kee, W.-S., Cho, D.-L., Kim, B.C. and Jin, K. (2005) Geological report of the Pocheon Sheet (1:50,000). Korea Institute of Geoscience and Mineral Resources, 69p. (in Korean with English summary)
  16. Kee, W.-S., Lim, S.-B., Kim, H., Kim, B.C., Hwang, S.K., Song, K.-Y. and Kihm, Y.,-H. (2008) Geological report of the Yeoncheon Sheet (1:50,000). Korea Institute of Geoscience and Mineral Resources, 83p. (in Korean with English summary)
  17. Korea Institute of Geoscience and Mineral Resources (KIGAM) (2001) 1:1,000,000 Tectonic Map of Korea.
  18. Kwon, S., Sajeev, K, Mitra, G., Park, Y, Kim, S.W. and Ryu, I.C. (2009) Evidence of Triassic collision in Far East Asia: the Korean collisional orogen. Earth and Planetary Science Letters, v.279, p.340-349. doi: 10.1016/j.epsl.2009.01.016
  19. Kim, H.S., Kwon S., Kim, S.W. and Santosh, M. (2018) Permo-Triassic high-pressure metamorphism in the central western Korean Peninsula, and its link to Paleo-Tethyan Ocean closure: Key issues revisited. Geoscience Frontiers, v.9, p.1325-1335. doi: 10.1016/j.gsf.2018.01.007
  20. Kim, I., Kim, A.-J., Woo, H. and Park, S.-I. (2019) Geological Structures of the Taean Formation in the Gomseom Area, Southwestern Gyeonggi Massif. Economic and Environmental Geology, v.52, p.159-168 (in Korean with English abstract). doi: 10.9719/EEG.2019.52.2.159
  21. Kim, J.-N., Ree, J.-H, Kwon, S.T., Park, Y., Choi, S.-J. and Cheong, C.-S. (2000) The Kyeonggi shear zone of the central Korean peninsula: Late orogenic imprint of the North and South China collision. The Journal of Geology, v.108, p.469-478. doi: 10.1086/314412
  22. Kim, O.J. (1973) The Stratigraphy and Geologic Structure of the Metamorphic Complex in the Northwestern Area of the Kyonggi Massif. Journal of the Korean Institute of Mining Geology, v.6, p.201-218 (in Korean with English abstract).
  23. Kim, S.W., Oh, C.W., Williams, I. S., Rubbato, D., Ryu, I.-C., Rajesh, V.J., Kim, C.-B., Guo, J. and Zhai, M. (2006) Phanerozoic high-pressure eclogite and intermediate-pressure granulite facies metamorphism in the Gyeonggi Block, South Korea: implications for the eastward extension of the Dabie-Sulu continental collision zone. Lithosphere, v.92, p.357-377. doi: 10.1016/j.lithos.2006.03.050
  24. Kim, S.W., Santosh, M., Park, N. and Kwon, S. (2011) Forearc serpentinite melange from the Hongseong suture, South Korea. Gondwana Research, v.20, p.852-864. doi: 10.1016/j.gr.2011.01.012
  25. Lee, B.Y., Oh, C.W., Cho, D.L., Zhai, M., Lee, B.C., Peng, P. and Yi, K. (2019) The Devonian back-arc basin and Triassic arc-continent collision along the Imjingang belt in the Korean Peninsula and their tectonic meaning. Lithos, v.328-329, p.276-296. doi: 10.1016/j.lithos.2019.01.011
  26. Marshak, S. and Mitra, G. (1988) Basic Methods of Structural Geology. Prentice Hall, New Jersey, 446p.
  27. Metcalfe, I. (2006) Paleozoic and Mesozoic tectonic evolution and paleography of East Asian crustal fragments: The Korean Peninsula in context. Gondwana Research, v.9, p.24-46. doi: 10.1016/j.gr.2005.04.002
  28. Mitra, G. (1978) Ductile deformation zones and mylonites: the mechanical processes involved in the formation of crytstalline basement rocks. American Journal of Science, v.278, p.1057-1084. doi: 10.2475/ajs.278.8.1057
  29. Oh, C.W., Kim, S.W., Choi, S.G., Zhai, M., Guo, J. and Sajeev, K. (2005) First finding of eclogite facies metamorphic event in South Korea and its correlation with the Dabie-Sulu collision belt in China. Journal of Geology, v.113, p.226-232. doi: 10.1086/427671
  30. Omori, S. and Isozaki, Y. (2011) Paleozoic Japan and the Eastern Extension of the collisional suture between the North and South China Cratons. Journal of Geography, v.120, p.40-51. doi: 10.5026/jgeography.120.40
  31. Park, S.-I. (2017) A Preliminary Study on the Exhumation Mechanism of the Paleozoic Gwangcheon Gneiss in the Southwestern Margin of the Gyeonggi Massif. Economic and Environmental Geology, v.50, p.525-535 (in Korean with English abstract). doi: 10.9719/EEG.2017.50.6.525
  32. Passchier, C.W. and Trouw, R.A.J. (2005) Microtectonics. Springer-Verlag, Berlin, 366p.
  33. Ramsay, J.G. and Huber, M.I. (1987) The Techniques of Modern Structural Geology. vol. 2: Folds and Fractures, Academic Press, London, 700p.
  34. Ree, J.-H., Cho, M., Kwon, S.-T. and Nakamura, E. (1996) Possible eastward extension of Chinese collision belt in South-Korea: the Imjingang belt. Geology, v.24, p.1071-1074. doi: 10.1130/0091-7613(1996)024<1071:peeocc>2.3.co;2
  35. Ree, J.-H., Kwon, S.-H., Park, Y., Kwon, S.-T. and Park, S.-H. (2001) Pretectonic and posttectonic emplacements of the granitoids in the south central Okcheon belt, South Korea: Implications for the timing of strike-slip shearing and thrusting. Tectonics, v.20, p.850-867. doi: 10.1029/2000tc001267
  36. Sajeev, K., Jeong, J., Kwon, S., Kee, W.-S., Kim, S.W., Komiya, T., Itaya, T., Jung, H.-S. and Park, Y. (2010) High P-T granulite relicts from the Imjingang Belt, South Korea: tectonic significance. Gondwana Research, v.17, p.75-86. doi: 10.1016/j.gr.2009.07.001
  37. Simpson, C. (1985) Deformation of granitic rocks across the brittleductile transition. Journal of Structural Geology, v.7, p.503-511. doi: 10.1016/0191-8141(85)90023-9
  38. Stallard, A. and Hickey, K. (2001) Fold mechanisms in the Carton Schist: Constraints on the contribution of flexural flow. Journal of Structural Geology, v.23, p.1865-1881. doi: 10.1016/s0191-8141(01)00032-3
  39. Stipp, M., Stunitz, H., Heilbronner, R. and Schmid, S.M. (2002a) The eastern Tonale fault zone: a 'natural laboratory' for crystal plastic deformation of quartz over a temperature range from 250 to 700 ℃. Journal of Structural Geology, v.24, p.1861-1884. doi: 10.1016/s0191-8141(02)00035-4
  40. Stipp, M., Stunitz, H., Heilbronner, R. and Schmid, S.M. (2002b). Dynamic recrystallization of quartz: correlation between natural and experimental conditions. In: De Meer, S., Drury, M.R., De Bresser, J.H.P., Pennock, G.M. (Eds.), Deformation Mechanism, Rheology and Tectonics: Current Status and Future Perspectives vol. 200, Special Publications of the Geological Society of London: London, UK, p.171-190. doi: 10.1144/gsl.sp.2001.200.01.11
  41. Tullis, J. and Yund, R.A. (1987) Transition from cataclastic flow to dislocation creep of feldspar: Mechanisms and microstructure, Geology, v.15, p.606-609. doi: 10.1130/0091-7613(1987)15<606:tfcftd>2.0.co;2
  42. Yin, A. and Nie, S. (1993) An indentation model for the north and south China collision and the development of the Tan-Lu and Honam fault systems, eastern Asia. Tectonics, v.12, p.801-813. doi: 10.1029/93tc00313
  43. Zhai, M.G., Guo, J., Li, Z., Chen, D., Peng, P., Li, T., Hou, Q. and Fan, Q. (2007) Linking the Sulu UHP belt to the Korean Peninsula: evidence from eclogite, Precambrian basement, and Paleozoic sedimentary basins. Gondwana Research, v.12, p.388-403. doi: 10.1016/j.gr.2007.02.003