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Econ. Environ. Geol. 2023; 56(6): 831-846

Published online December 29, 2023

https://doi.org/10.9719/EEG.2023.56.6.831

© THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY

Preliminary Structural Geometry Interpretation of the Pyeongchang Area in the Northwestern Taebaeksan Zone, Okcheon Belt: A Klippe Model

Heunggi Lee1,2, Yirang Jang3,*, Sanghoon Kwon1

1Department of Earth System Sciences, Yonsei University, Seoul 03722, Republic of Korea
2Gajaeul High School, Seoul 03709, Republic of Korea
3Department of Earth and Environmental Sciences, Chonnam National University, Gwangju 61186, Republic of Korea

Correspondence to : *yirang@jnu.ac.kr

Received: December 15, 2023; Revised: December 20, 2023; Accepted: December 21, 2023

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided original work is properly cited.

Abstract

The Jucheon-Pyeongchang area in the northwestern Taebaeksan Zone of the Okcheon fold-thrust belt preserved several thrust faults placing the Precambrian basement granite gneisses of the Gyeonggi Massif on top of the Early Paleozoic Joseon Supergroup and the age-unknown Bangrim Group. Especially, the thrust faults in the study area show the closed-loop patterns on the map view, showing older allochthonous strata surrounded by younger autochthonous or para-autochthonous strata. These basement-involved thrusts including Klippes will provide important information on the hinterland portion of the fold-thrust belt. For defining Klippe geometry in the thrust fault terrains of the Jucheon-Pyeongchang area by older on younger relationship, the stratigraphic position of the age-unknown Bangrim Group should be determined. The Middle Cambrian maximum depositional age by the detrital zircon SHRIMP U-Pb method from this study, together with field relations and previous research results suggest that the Bangrim Group overlies the Precambrian basement rocks by nonconformity and underlies the Cambrian Yangdeok Group (Jangsan and Myobong formations). The structural geometric interpretation of the Pyeongchang area based on newly defined stratigraphy indicates that the Wungyori and Barngrim thrusts are the same folded thrust, and can be interpreted as a Klippe, having Precambrian hanging wall granite gneisses surrounded by younger Cambrian strata of the Joseon Supergroup and the Bangrim Group. Further detailed structural studies on the Jucheon-Pyeongchang area can give crucial insights into the basement-involved deformation during the structural evolution of the Okcheon Belt.

Keywords Okcheon Belt, Bangrim Group, Bangrim thrust, Wungyori thrust, Klippe Model

옥천대 북서부 태백산지역 평창 일대의 클리페 모델 기반 구조기하 형태 해석 예비 연구

이흥기1,2 · 장이랑3,* · 권상훈1

1연세대학교 이과대학 지구시스템과학과
2가재울고등학교
3전남대학교 자연과학대학 지구환경과학부 지질환경전공

요 약

한반도의 대표적인 습곡-단층대 중 하나인 옥천대의 주천-평창지역에는 경기육괴 기반암을 고생대 조선누층군 및 시대미상의 방림층군 상위로 충상시키는 다수의 트러스트 단층이 발달한다. 이 지역의 트러스트들은 상반의 암체가 하반의 암체로 완전히 둘러싸인 폐곡선 형태의 독특한 자취를 보이며, 이는 전형적인 클리페의 지질도 상 특징으로 해석될 수 있다. 특히, 연구 지역과 같이 트러스트 상반에 기반암을 포함하는 클리페의 경우에는 습곡-단층대 배후지의 구조 발달을 이해하는데 중요하다. 그러나 클리페 구조가 잘 정의되기 위해서는 층서적으로 오래된 암체가 트러스트를 경계로 상대적으로 젊은 암체의 상위에 구조적으로 완전히 고립된 형태를 보여야 하기 때문에, 연구지역에 넓게 분포하는 시대미상 방림층군의 지질연대가 매우 중요하다. 본 연구에서는 SHRIMP U-Pb 저어콘 연대측정을 통해 획득한 방림층군의 최대 퇴적시기와 야외조사 결과 및 기존 연구를 종합하여, 방림층군을 아래로는 선캄브리아시대 화강편마암과 위로는 전기 고생대 조선누층군 양덕층군(장산층, 묘봉층)의 지층 사이에 놓이는 고생대 캄브리아기 최하부 지층에 대비하였다. 이를 바탕으로 평창지역에 대한 구조기하 형태 연구를 수행한 결과, 운교리트러스트와 방림트러스트는 하나의 습곡된 트러스트이며 운교리트러스트 상반의 암체들이 하반 암체들에 의해 완전히 고립된 특징을 보이는 클리페 모델로 해석이 가능함을 확인하였다. 향후 주천-평창지역에 대한 구조지질학적 측면의 후속 연구들을 통해 클리페 모델에 대한 추가적인 테스트가 이루어진다면, 옥천대의 구조 진화에 있어서 기반암을 포함하는 변형 기작의 역할에 대해 중요한 정보를 획득할 수 있을 것이다.

주요어 옥천대, 방림층군, 방림트러스트, 운교리트러스트, 클리페 모델

Article

Short Note

Econ. Environ. Geol. 2023; 56(6): 831-846

Published online December 29, 2023 https://doi.org/10.9719/EEG.2023.56.6.831

Copyright © THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY.

Preliminary Structural Geometry Interpretation of the Pyeongchang Area in the Northwestern Taebaeksan Zone, Okcheon Belt: A Klippe Model

Heunggi Lee1,2, Yirang Jang3,*, Sanghoon Kwon1

1Department of Earth System Sciences, Yonsei University, Seoul 03722, Republic of Korea
2Gajaeul High School, Seoul 03709, Republic of Korea
3Department of Earth and Environmental Sciences, Chonnam National University, Gwangju 61186, Republic of Korea

Correspondence to:*yirang@jnu.ac.kr

Received: December 15, 2023; Revised: December 20, 2023; Accepted: December 21, 2023

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided original work is properly cited.

Abstract

The Jucheon-Pyeongchang area in the northwestern Taebaeksan Zone of the Okcheon fold-thrust belt preserved several thrust faults placing the Precambrian basement granite gneisses of the Gyeonggi Massif on top of the Early Paleozoic Joseon Supergroup and the age-unknown Bangrim Group. Especially, the thrust faults in the study area show the closed-loop patterns on the map view, showing older allochthonous strata surrounded by younger autochthonous or para-autochthonous strata. These basement-involved thrusts including Klippes will provide important information on the hinterland portion of the fold-thrust belt. For defining Klippe geometry in the thrust fault terrains of the Jucheon-Pyeongchang area by older on younger relationship, the stratigraphic position of the age-unknown Bangrim Group should be determined. The Middle Cambrian maximum depositional age by the detrital zircon SHRIMP U-Pb method from this study, together with field relations and previous research results suggest that the Bangrim Group overlies the Precambrian basement rocks by nonconformity and underlies the Cambrian Yangdeok Group (Jangsan and Myobong formations). The structural geometric interpretation of the Pyeongchang area based on newly defined stratigraphy indicates that the Wungyori and Barngrim thrusts are the same folded thrust, and can be interpreted as a Klippe, having Precambrian hanging wall granite gneisses surrounded by younger Cambrian strata of the Joseon Supergroup and the Bangrim Group. Further detailed structural studies on the Jucheon-Pyeongchang area can give crucial insights into the basement-involved deformation during the structural evolution of the Okcheon Belt.

Keywords Okcheon Belt, Bangrim Group, Bangrim thrust, Wungyori thrust, Klippe Model

옥천대 북서부 태백산지역 평창 일대의 클리페 모델 기반 구조기하 형태 해석 예비 연구

이흥기1,2 · 장이랑3,* · 권상훈1

1연세대학교 이과대학 지구시스템과학과
2가재울고등학교
3전남대학교 자연과학대학 지구환경과학부 지질환경전공

Received: December 15, 2023; Revised: December 20, 2023; Accepted: December 21, 2023

요 약

한반도의 대표적인 습곡-단층대 중 하나인 옥천대의 주천-평창지역에는 경기육괴 기반암을 고생대 조선누층군 및 시대미상의 방림층군 상위로 충상시키는 다수의 트러스트 단층이 발달한다. 이 지역의 트러스트들은 상반의 암체가 하반의 암체로 완전히 둘러싸인 폐곡선 형태의 독특한 자취를 보이며, 이는 전형적인 클리페의 지질도 상 특징으로 해석될 수 있다. 특히, 연구 지역과 같이 트러스트 상반에 기반암을 포함하는 클리페의 경우에는 습곡-단층대 배후지의 구조 발달을 이해하는데 중요하다. 그러나 클리페 구조가 잘 정의되기 위해서는 층서적으로 오래된 암체가 트러스트를 경계로 상대적으로 젊은 암체의 상위에 구조적으로 완전히 고립된 형태를 보여야 하기 때문에, 연구지역에 넓게 분포하는 시대미상 방림층군의 지질연대가 매우 중요하다. 본 연구에서는 SHRIMP U-Pb 저어콘 연대측정을 통해 획득한 방림층군의 최대 퇴적시기와 야외조사 결과 및 기존 연구를 종합하여, 방림층군을 아래로는 선캄브리아시대 화강편마암과 위로는 전기 고생대 조선누층군 양덕층군(장산층, 묘봉층)의 지층 사이에 놓이는 고생대 캄브리아기 최하부 지층에 대비하였다. 이를 바탕으로 평창지역에 대한 구조기하 형태 연구를 수행한 결과, 운교리트러스트와 방림트러스트는 하나의 습곡된 트러스트이며 운교리트러스트 상반의 암체들이 하반 암체들에 의해 완전히 고립된 특징을 보이는 클리페 모델로 해석이 가능함을 확인하였다. 향후 주천-평창지역에 대한 구조지질학적 측면의 후속 연구들을 통해 클리페 모델에 대한 추가적인 테스트가 이루어진다면, 옥천대의 구조 진화에 있어서 기반암을 포함하는 변형 기작의 역할에 대해 중요한 정보를 획득할 수 있을 것이다.

주요어 옥천대, 방림층군, 방림트러스트, 운교리트러스트, 클리페 모델

    Fig 1.

    Figure 1.(a) Tectonic map of the Korean Peninsula (modified after a 1:1,000,000 tectonic map of Korea; Kee et al., 2019). (b) Geologic map of the Jucheon-Pyeongchang area in the northwestern Taebaeksan Zone of the Okcheon Belt (modified after Cheong et al., 1979; Hong et al., 1995). CN-Chungdaegalbong nappe; TK-Turuanji klippe; WK-Wachon klippe.
    Economic and Environmental Geology 2023; 56: 831-846https://doi.org/10.9719/EEG.2023.56.6.831

    Fig 2.

    Figure 2.Field photographs of the Bangrim thrust in the central part of the Pyeongchang area showing (a) dark gray schist of the Myobong Formation (Location: N37°30′15.9″, E128°24′43.4″) lying on (b) light gray laminated limestone of the Jeongseon Formation (Location: N37°30′15.7″, E128°24′40.7″) in the Sogaedong valley, and (c) dark gray schist of the Myobong Formation (Location: N37°29′09.3″, E128°24′26.1″) lying on (d) light gray laminated limestone of the Jeongseon Formation (Location: N37°29′14.6″, E128°24′33.8″) in the Sanggaesu valley. Geological hammer for scale (32 cm).
    Economic and Environmental Geology 2023; 56: 831-846https://doi.org/10.9719/EEG.2023.56.6.831

    Fig 3.

    Figure 3.Field photographs of the Wachon klippe showing (a) the Precambrian granite gneiss (Location: N37°18′51.2″, E128°17′39.1″) lying on (b) the younger Bangrim Group (Location: N37°18′55.0″, E128°17′34.8″) in the Danggeori Valley, and (c) the Precambrian granite gneiss lying on (d) the younger Bangrim Group in the Panunri area (Location: N37°19′06.5″, E128°18′56.1″). Geological Hammer for scale (32 cm).
    Economic and Environmental Geology 2023; 56: 831-846https://doi.org/10.9719/EEG.2023.56.6.831

    Fig 4.

    Figure 4.(a) Field photograph of the Wachon klippe. Outcrop photographs showing (b) greenish mica schist of the younger Bangrim Group overlain by (c) mylonite of the Precambrian granite gneiss in the Myeongmadong Valley (Location: N37°17′48.6″, E128°17′42.0″). Pen for scale (14 cm). Insets in (a) indicate the areas for (b) and (c).
    Economic and Environmental Geology 2023; 56: 831-846https://doi.org/10.9719/EEG.2023.56.6.831

    Fig 5.

    Figure 5.Field photographs of the Wungyori thrust, showing (a) mica-schist of the Bangrim Group is overlain by (b) mylonite of the Precambrian granite gneiss in the Weonteogol valley (Location: N37°26′11.1″, E128°19′50.8″), and (c) quartz veined mica-schist of the Bangrim Group is overlain by (d) mylonite of the Precambrian granite gneiss in the Hanggol valley (Location: N37°31′00.9″, E128° 22′10.1″). Geological hammer for scale (32 cm).
    Economic and Environmental Geology 2023; 56: 831-846https://doi.org/10.9719/EEG.2023.56.6.831

    Fig 6.

    Figure 6.(a) and (b) Outcrop photographs of the collected sample from the quartzite layer within the Bangrim Group. (c) Scanning electron microscope cathodoluminescence (CL) image of sectioned zircon grains. (d) Tera–Wasserburg concordia and (e) probability density plots of the SHRIMP U-Pb isotopic data of zircons from the Bangrim Group (sample BR-3A).
    Economic and Environmental Geology 2023; 56: 831-846https://doi.org/10.9719/EEG.2023.56.6.831

    Fig 7.

    Figure 7.Field photograph of the unconformity between the Precambrian granite gneiss and the Bangrim Group showing (a) the outcrop of the unconformity (005°, 25°SE) from the Panun valley (Kihm et al., 2010; Location: N37°21′07.2″, E128°18′23.7″). (b) Field photograph of the Precambrian granite gneiss (048°, 24°SE) under the unconformity from the Danggeori Valley (Location: N37°19′11.4″, E128°17′11.5″). Geological hammer for scale (32 cm).
    Economic and Environmental Geology 2023; 56: 831-846https://doi.org/10.9719/EEG.2023.56.6.831

    Fig 8.

    Figure 8.(a) Previously published 1:50,000 geologic map (after Cheong et al., 1979; Hong et al., 1995) and (b) modified geologic map, showing the major structures of the Pyeongchang area. Profiles of the Pyeongchang area along (c) northern (A-A’), (d) central (B-B’), and (e) southern (C-C’) parts based on cross-section interpretation following a Klippe model. BT-Bangrim thrust; WT-Wungyori thrust.
    Economic and Environmental Geology 2023; 56: 831-846https://doi.org/10.9719/EEG.2023.56.6.831

    U-Pb zircon isotopic data of the analyzed samples from the Bangrim Group..


    Grain spotU (ppm)Th (ppm)Th/U238U/206Pb*± (%)207Pb*/206Pb± (%)Apparent ages (Ma)Discordant (%)
    206Pb/206Pb±207Pb/238U±
    BR-3A
    BR3A-1.19831250.138.9179221.2195610.0623000.783576685.18.6684.516.6-0
    BR3A-10.11316700.058.3547552.1224250.0688953.769206723.817.2895.775.8+8
    BR3A-11.14952120.443.6809251.2380610.0965390.3952801547.919.51558.37.4+0
    BR3A-12.14612320.515.1170271.7918810.0820011.0829061144.921.11245.521.2+9
    BR3A-13.17033670.546.1483190.3642820.0725350.423630970.13.81001.18.4+2
    BR3A-14.14052570.653.6397250.9560980.0972930.2455371563.415.11572.94.6+1
    BR3A-15.1375820.228.0679953.0272890.0671950.871574750.222.3843.918.0+1
    BR3A-16.1557850.166.1235000.6659180.0726590.569994973.86.81004.511.4+0
    BR3A-17.1621650.117.7564281.2041780.0652910.530438781.59.4783.711.2-0
    BR3A-18.11941480.785.3596843.7584570.0763210.1850871102.340.01103.53.8-16
    BR3A-19.112802570.219.2863861.1134010.0628630.287133658.27.3703.76.0-2
    BR3A-2.14575241.183.3682620.6752290.1083460.2228781663.011.61771.94.0-2
    BR3A-20.11343230.025.2615241.4924580.0774930.3403151120.916.51133.96.8+1
    BR3A-21.11008620.062.3271381.0253860.1528200.1661702280.626.52377.72.8+3
    BR3A-22.16731860.289.6235901.2432230.0606060.496304637.58.0625.310.6-2
    BR3A-23.111663720.3312.2568282.1855640.0579950.307059505.110.9529.76.6-3
    BR3A-24.110761080.108.8960310.9179810.0618150.212246687.16.3667.74.6-1
    BR3A-25.1360540.153.5129592.4006190.0981930.2793271617.538.81590.15.2-1
    BR3A-26.114291230.098.3220300.7768280.0663350.331424729.05.7816.97.0-6
    BR3A-27.12331530.675.2456100.9907540.0775930.4634191123.911.21136.59.2-2
    BR3A-28.12821640.6012.3651271.5566210.0574300.673008501.27.9508.114.8+1
    BR3A-29.176180.243.3009352.0928790.1197383.1758481669.642.71952.355.6+6
    BR3A-3.16574110.643.7074721.3824640.0958290.3415761538.521.41544.56.4+1
    BR3A-30.11732271.354.6502401.1405640.0824351.0390921255.115.01255.920.2+1
    BR3A-31.19261460.165.7925520.9962490.0733920.4484261026.610.31024.99.0-0
    BR3A-32.14451940.459.2406750.7953260.0606400.364065663.25.3626.57.8-0
    BR3A-33.14582900.6510.2020151.1414930.0604310.472278602.47.0619.110.2-4
    BR3A-34.15341370.264.9039070.7189270.0802993.2173691195.612.21204.362.2+1
    BR3A-35.15611780.334.4140571.6201000.0884840.0833261310.320.71393.11.6+1
    BR3A-36.11532440.039.5789700.9157400.0614940.513204639.76.0656.511.0+1
    BR3A-37.13541480.434.5159450.9001320.0841880.5083771288.711.91296.99.8+0
    BR3A-38.11521100.745.5628421.0741510.0760160.8986931063.912.01095.517.8+1
    BR3A-39.110552400.238.6118061.4274240.0631540.675219708.010.2713.514.2-1
    BR3A-4.15327561.464.9774851.0268250.0794560.5659391179.912.51183.511.2-1
    BR3A-40.12991770.614.1563851.7145250.0929810.4901341380.823.71487.59.2+2
    BR3A-41.11882131.169.6841371.6779610.0608320.908471633.410.7633.319.4+1
    BR3A-42.14272830.689.1076720.8979620.0615360.084585671.96.0658.11.8-2
    BR3A-43.14153220.803.1469660.9846320.1099620.1292821775.517.81798.72.4+1
    BR3A-44.12642821.105.9891021.2065880.0726990.487844994.712.01005.79.8+1
    BR3A-45.16042880.492.8826420.7912710.1235250.5131901903.417.12007.79.2+2
    BR3A-46.1138940.7012.2155950.4522950.0574471.500692507.22.9508.732.8-2
    BR3A-47.17451640.239.2669791.0353720.0618990.402772660.36.8670.78.6-0
    BR3A-48.146330.758.9337002.7434940.0624813.283363683.820.0690.768.4+5
    BR3A-49.1919950.119.7592720.7231130.0609430.917678628.64.9637.319.6+1
    BR3A-5.11234820.078.7504011.1348220.0640650.405059696.27.9743.78.6+2
    BR3A-50.1873330.048.6676492.1240850.0630030.489392703.714.8708.310.4+0
    BR3A-51.18644740.565.7363380.9146360.0750390.8378131034.110.01069.516.8+10
    BR3A-52.11582121.373.9981062.6386180.0932503.0697511433.441.81492.957.0+2
    BR3A-53.15336631.2812.3781041.1978040.0572340.863574500.86.2500.519.00
    BR3A-54.13231520.484.6010991.2739290.0830340.3208801267.516.11270.16.2-2
    BR3A-55.15671030.193.0752190.9882950.1089160.3528401819.919.01781.36.6-1
    BR3A-56.113612840.214.6883950.9602160.0813630.2936581247.311.91230.35.6-1
    BR3A-57.13203141.004.5894921.7082090.0829870.4612991270.621.61268.99.0-1
    BR3A-58.13962480.645.0342191.3219760.0787920.3033701167.915.21166.96.0-1
    BR3A-59.1445650.159.1126530.7073060.0619871.439194671.15.4673.730.4-2
    BR3A-6.1951350.042.8451551.5975720.1301870.8284271910.733.92100.514.4+4
    BR3A-60.11118650.065.3495810.6804610.0753460.1219841106.17.41077.72.6-1
    BR3A-61.17654550.615.5394850.8634400.0756540.5790201068.89.51085.911.6+10
    BR3A-62.14332470.584.3668581.6203580.0837144.0637681332.526.81285.977.2+1
    BR3A-63.12672490.9612.0998242.1303560.0562630.724886512.610.9462.716.0+4
    BR3A-64.13032130.724.1515941.4198580.0889870.5920851389.820.01403.911.2+0
    BR3A-65.11841300.726.2760062.4779870.0709610.590775952.623.2956.312.0-1
    BR3A-66.1284120.045.9542520.9768720.0724511.9628461000.911.3998.739.40
    BR3A-67.12061200.6012.3289090.9641080.0559772.999855503.55.8451.565.2-4
    BR3A-68.12764421.647.5464070.8805220.0648081.171000803.27.6768.124.4-9
    BR3A-69.13172400.787.6784351.0584420.0646601.215951789.98.8763.325.4-5
    BR3A-7.12771720.646.1485210.6093000.0726391.086723969.86.61003.922.0+1
    BR3A-70.12752871.077.1879211.4555970.0642980.421758842.612.2751.58.8-9
    BR3A-71.12102061.0112.4499471.0612830.0564611.312896498.55.7470.528.8-7
    BR3A-72.122351.635.2506532.4782920.0771143.5677331123.830.81124.169.6+4
    BR3A-73.164811.304.7445371.3513100.0822410.3704001231.016.51251.37.2+2
    BR3A-74.158113102.3110.3004791.6520530.0591770.750025597.79.9573.716.20
    BR3A-75.11961470.778.5451291.0813950.0642591.243911712.38.1750.126.2+1
    BR3A-76.1154850.5712.1919551.2464570.0575831.243845508.06.6513.927.2-4
    BR3A-77.194710.774.4050990.7379030.0832521.0788551321.911.01275.121.0-2
    BR3A-78.1202970.496.3531011.0387190.0705781.316581942.210.7945.326.6-0
    BR3A-79.184931.143.3925461.0431330.1022320.1913491665.217.61665.13.4-2
    BR3A-8.120771350.0711.7964160.9032280.0581520.346784524.34.8535.57.6+2
    BR3A-80.11381280.953.6208761.3018860.0971870.6132601572.121.41570.911.4+0
    BR3A-9.1830440.058.6572404.0481260.0665882.522466701.028.6824.951.8+6

    Errors are 1-sigma; Pbc and Pb* indicate the common and radiogenic portions, respectively..


    KSEEG
    Apr 30, 2024 Vol.57 No.2, pp. 107~280

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