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Revised Geology and Geological Structures of the Northeastern Chungnam Basin in the Southwestern Korean Peninsula
Econ. Environ. Geol. 2022 Dec;55(6):597-616
Published online December 31, 2022;  https://doi.org/10.9719/EEG.2022.55.6.597
Copyright © 2022 The Korean Society of Economic and Environmental Geology.

Yujung Kwak1, Seung-Ik Park1, Jeong-Yeong Park1,2,*, Taejin Choi3, Eun Hye Jeong4

1Department of Geology, Kyungpook National University, Daegu 41566, Republic of Korea
2Geological Research Center, Korea Institute of Geoscience and Mineral Resources, Daejeon 34132, Republic of Korea
3Department of Earth Science Education, Korea National University of Education, Cheongju 28173, Republic of Korea
4Korea Mine Rehabilitation and Mineral Resources Corporation, Wonju 26464, Republic of Korea
Received November 28, 2022; Revised December 9, 2022; Accepted December 10, 2022.
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 the original work is properly cited.
 Abstract
The Chungnam basin is a crucial area for studying the Mesozoic crustal evolutionary history of the Korean Peninsula. This study reports the revised geology and new isotopic ages from the northeastern Chungnam Basin based on detailed geological mapping and LA-ICP-MS zircon U-Pb analysis. Our renewed geologic map defines intra-basin, basin-bounding, and basement fault systems closely related to hydrothermal gold-bearing quartz vein injections. Here, we propose the directions of (micro)structural and geochronological future work to address issues on the relationship between the tectonic process, basin evolution, and hydrothermal fluid migration in the southwestern Korean Peninsula.
Keywords : Mesozoic tectonics, Chungnam Basin, zircon U-Pb age dating, basin inversion, crustal fluid redistribution
Research Highlights
  • A new geological map in the northeastern Chungnam Basin is presented based on a detailed field survey and zircon U-Pb analysis.

  • The study area exposes six lithologic units preserving evidence of Mesozoic two-phase extension and subsequent basin inversion.

  • Gold-bearing quartz veins filling inversion-related fault systems reflect hydrothermal fluid migration in a structurally inverted basin.

1. Introduction

The southwestern Korean Peninsula records a complex crustal evolutionary history related to Mesozoic orogenic cycles (Oh et al., 2005; Kim et al., 2006, 2011, 2015, 2021; Egawa and Lee, 2008; Choi et al., 2009; Kwon et al., 2009; Cho et al., 2017; Park and Park, 2020). The Late Triassic post-collisional thermo-mechanical processes following a continental collision event caused the formation of extensional non-marine basins, including the Chungnam Basin in this area (de Jong et al., 2015; Park et al., 2018; Lee et al., 2021). Although controversial models exist on the formation and evolution of the basins (e.g., Jeon et al., 2007; Egawa and Lee, 2009; Lim and Cho, 2012), recent studies suggested that the change in governing tectonics from collision to subduction led to further subsidence and subsequent structural inversion of the basin during the Jurassic to Early Cretaceous (Park and Noh, 2015; Park et al., 2018, 2019).

The Chungnam Basin and adjacent area (Fig. 1) have been attracting considerable interest due to the presence of coal fields and mineral deposits (e.g., Chungnam coalfield and Samgwang gold-silver deposit: Chun et al. 1987, 1990; So and Shelton, 1987; So et al., 1988; Yoo et al., 2002, 2009, 2010). The Chungnam basin records evidence of two-phase subsidences related to the Late Triassic to Early Jurassic post-collisional (viz., Nampo Group) and the Early to Middle Jurassic intra-arc (viz., Oseosan Volcanic Complex) processes (Choi et al., 1987; Kim and Kim, 1998; Kim and Lee, 2015; Park et al., 2018, 2019; Lee et al., 2021). The Nampo Group is composed of the Hajo, Amisan, Jogyeri, Baegunsa, and Seongjuri Formations in ascending order (Chun et al., 1987, 1990; Lee et al., 2021). The Oseosan Volcanic Complex mainly consists of rhyolitic tuff and tuffaceous sedimentary rocks (Park et al., 2018). In this study, we report a new geologic map (Fig. 2) of the Sindaeri area in the northeastern Chungnam Basin, focusing on a complex fault system and its control on the distribution of main lithologic units and hydrothermal veins, through detailed mapping and zircon U-Pb age dating. Based on this map, we briefly discuss insights into the Mesozoic orogenic cycles in the southwestern Korean Peninsula and propose necessary future studies to solve the issues regarding the relationship between tectonics, basin evolution, and crustal fluid redistribution.

Figure 1. (a) General tectonic map of the Korean Peninsula (redrawn after Kee et al., 2019). Abbreviations: GwM, Gwanmo Massif; NM, Nangnim Massif; GM, Gyeonggi Massif; YM, Yeongnam Massif; DB, Dumangang Belt; MB, Macheollyeong Belt; HIB, Hongseong–Imjingang Belt; OB, Okcheon Belt; G–MB, Gilju–Myeongcheon Basin; PB, Pyeongnam Basin; TB, Taebaeksan Basin; GB, Gyeongsang Basin; YeB, Yeonil Basin; BVP, Baekdusan Volcanic Plateau; JVT, Jeju Volcanic Terrain. (b) Simplified geological map of the Chungnam Basin (Modified after Kee et al., 2019; Park et al., 2019).
Figure 2. New geological map and cross sections of the study area.
2. Lithologic Units

Detailed geological fieldwork was conducted to revise the geological map of the study area (Fig. 2). The lithology of the study area is divided into six units, viz., Paleo-proterozoic metamorphic basement rocks, age unknown metapsammite, Late Triassic to Early Jurassic sandstone, Middle Jurassic rhyolitic tuff and tuffaceous sedimentary rocks, and Early Cretaceous quartz vein. The protolith age of each lithologic unit is adopted from previously published isotopic age or determined by new zircon U-Pb analysis in the present study. The description of each lithologic unit is mentioned in the following sections.

2.1. Paleoproterozoic Metamorphic Basement Rocks

Paleoproterozoic metamorphic basement rock is most widely distributed in the study area. This lithologic unit primarily comprises granitic gneiss, banded gneiss, and mica schist.

The granitic gneiss is yellowish brown to bluish gray and equigranular (0.5–2 mm; Fig. 3a). It is primarily composed of quartz, plagioclase, alkali feldspar, biotite, and muscovite (Fig. 3b). Aggregates of quartz and feldspar of approximately 1–3 cm in size often occur. Almost every quartz grain has sutured boundaries and shows patchy undulatory extinction; some of them display polygonal-shaped subgrains. Feldspars are commonly altered into sericites.

Figure 3. Photographs of the Paleoproterozoic metamorphic basement rocks. (a) Outcrop of a granitic gneiss. (b) Cross-polarized light (XPL) image of a granitic gneiss. (c) Outcrop of a banded gneiss. (d) XPL image of a banded gneiss. (e) Hand specimen of a mica schist. (f) XPL image of a mica schist. Abbreviations: Qtz, Quartz; Ser, Sericite; Bt, Biotite; Ms, Muscovite.

The banded gneiss exhibits a gneissosity, defined by yellowish to grayish white leucosome and dark brown to gray melanosome, generally striking NE–SW and dipping southeastward (Fig. 3c). It displays augen texture in part. The lithology mainly consists of quartz, plagioclase, alkali feldspar, biotite, and muscovite, with minor chlorite, opaque minerals, and zircon (Fig. 3d). Quartz grains are sutured, bulged, and show patchy undulatory extinction. Feldspars are mostly altered into sericite, and some alkali feldspar shows exsolution lamellae. Biotites and chlorites are aligned parallel to the foliation, whereas muscovites occur rather irregularly (Fig. 3d).

The mica schist is dark gray and fine– to medium–grained (Fig. 3e). The general foliation attitude is the same as the banded gneiss. It is primarily composed of quartz, feldspar, muscovite, and biotite. Quartz grains show sutured boundaries and are segregated to form a foliation, and phyllosilicates are aligned parallel to the foliation (Fig. 3f).

It has been reported that the gneisses are the product of the Paleoproterozoic (ca. 1.88–1.85 Ga) igneous activity and subsequent migmatization and Late Triassic (ca. 230 Ma) metamorphism (Kim et al., 2008; Park et al., 2014; Cho et al., 2017).

2.2. Age-unknown Metapsammite

Age-unknown metapsammite exposes in the footwall of a NE-SW trending fault (viz., Gooksa Fault). The metapsammite is light brown to gray in color and composed mainly of quartz, sericite, and chlorite (Fig. 4a). Most quartz grains are less than 0.3 mm in size. They have subrounded to subangular roundness, occasionally showing sutured boundaries. In addition, this unit has a strong foliation defined by the alignment of phyllosilicate minerals (Fig. 4b).

Figure 4. Photographs of the age-unknown metapsammite. (a) Outcrop of a metapsammite. (b) XPL image of a metapsammite. Abbreviations: Qtz, Quartz; Ser, Sericite; Chl, Chlorite.

Our new U–Pb data from the detrital zircons in the metapsammite shows Precambrian ages except for one Mesozoic age, making it difficult to constrain the sedimentation age of the protolith. The details of the data are shown in the next chapter.

2.3. Late Triassic to Early Jurassic Sandstone

This unit is located in the eastern part of the Chungnam Basin in the study area. It contacts the Paleoproterozoic metamorphic basement rocks across an eastern basin-bounding fault. This lithologic unit dominantly comprises gray to dark gray, fine- to coarse-grained sandstone and involves coal seams (Fig. 5a). The sandstone is mainly composed of quartz and muscovite. In addition, opaque minerals, organic matter, and clay minerals are accessory minerals. The quartz grains are poorly sorted, subangular to angular, and slightly aligned to a bedding surface (Fig. 5b). This unit likely corresponds to the coal-bearing Baegunsa or Amisan Formation of the Nampo Group. The fossil age of the reported Dictyophyllum-Clathropteris floral province and zircon U–Pb age indicate Late Triassic–Early Jurassic deposition of the coal-bearing unit (Chun et al. 1987, 1990; Lee et al., 2019, 2021).

Figure 5. Photographs of the Late Triassic to Early Jurassic sandstone. (a) Outcrop of a sandstone. (b) XPL image of a sandstone. Abbreviations: Qtz, Quartz; Ms, Muscovite.

2.4. Middle Jurassic Rhyolitic Tuff

Middle Jurassic rhyolitic tuff contacts the Paleoproterozoic metamorphic basement rocks and the Late Triassic to Early Jurassic sandstone across the eastern and western basin-bounding faults and an intra-basin fault, respectively (Fig. 2). This unit is composed of tuff, lapilli tuff, and tuff breccia.

The tuff is light to dark gray, massive, and glassy (Fig. 6a). It contains feldspar and quartz crystal fragments up to 2 mm in size embedded in a glassy matrix and is locally welded (Fig. 6b). In fault contact regions, the tuff shows a shearing-related foliation in part.

Figure 6. Photographs of the Middle Jurassic rhyolitic tuff. (a) Outcrop of a massive tuff. (b) Outcrop of a welded tuff. (c) Outcrop of a lapilli tuff. (d) XPL image of a lapilli tuff. (e) Outcrop of a tuff breccia. (f) XPL image of a tuff breccia. Abbreviations: Qtz, Quartz; Pl, Plagioclase; Lf, Lithic fragment.

The lapilli tuff, the most common lithology in this unit, is yellowish white, bluish- to light gray, or dark gray (Fig. 6c). It includes mm- to cm-sized quartz and feldspar crystal and lithic fragments within a glassy matrix. The quartz crystals are subhedral to anhedral and show locally embayed and feathery textures (Fig. 6d). The lithic fragments are mainly volcanic rocks with minor sandstone, granite, and gneiss.

The tuff breccia locally exposes in the eastern part of this lithologic unit. It is a clast-supported breccia composed of lithic blocks (up to approximately 20 cm) embedded in a dark gray matrix (Fig. 6e). The blocks are mainly volcanic rocks with minor sandstone, granite, and gneiss (Fig. 6f). The matrix includes feldspars and quartz crystal fragments with embayed texture.

Our new U–Pb data from igneous zircons in a rhyolitic tuff sample shows a weighted mean age of ca. 169 Ma. The details of the data are shown in the next section.

2.5. Middle Jurassic Tuffaceous Sedimentary Rocks

Middle Jurassic tuffaceous sedimentary rocks are distributed on top of the rhyolitic tuff unit, contacting each other across intra-basin faults. This unit is composed of alternating layers of dark brown to dark gray fine sandstone, pebbly sandstone, and conglomerate (Fig. 7a). The fine sandstone is well-sorted, well-bedded, and comprises rounded to subangular grains (Fig. 7b). The pebbly sandstone and conglomerate are poorly-sorted and matrix-supported, and include generally rounded sandstone, volcanic rocks, quartzite, and gneiss clasts up to 15 cm in size. In this unit, the quartz grains partly show an embayed texture (Fig. 7c). In the region adjacent to the western basin-bounding fault, the tuffaceous sedimentary rocks exhibit strong foliation defined by the alignment of clasts and phyllosilicates in the matrix (Fig. 7d).

Figure 7. Photographs of the Middle Jurassic tuffaceous sedimentary rocks. (a) Outcrop of a tuffaceous sedimentary rock showing grain size change. (b, c) XPL images of a tuffaceous sandstone. (d) Outcrop of a foliated tuffaceous sedimentary rock.

2.6. Early Cretaceous Quartz Veins

Early Cretaceous quartz veins are widespread in the study area. The veins are divided into fault-filling shear veins, extension veins, and breccia veins based on their structural occurrence. The fault-filling shear veins are massive or laminated with a width ranging from approximately 10 cm to 3 m (Fig. 8a). They have blocky to elongate blocky texture (Fig. 8b). The extension veins are syntaxial and occur as <3 cm width veinlets (Fig. 8c). The extension veins frequently array near fault planes. Notably, the extension and shear veins often show a mutual cross-cutting relationship. The breccia veins occur near fault zones in host rocks (Fig. 8d). The fault-related brecciated zones have a width of about 1–2 m and are filled with µm– to cm–wide veins.

Figure 8. Photographs of the Early Cretaceous quartz veins. (a) Outcrop of a fault-filling laminated quartz vein. (b) XPL image of a fault-filling vein and extension veins. (c) Outcrop of extension veins. (d) Outcrop of a brecciated tuff near a fault plane.

The quartz veins are generally milky white and occasionally have dark yellowish to brownish parts containing sulfide minerals. They are composed chiefly of quartz and contain ankerite, pyrite, and electrum; some of them have been a target for mining gold-silver deposits (viz., Samgwang gold-silver deposit) (So and Shelton, 1987; So et al., 1988; Yoo et al., 2002, 2009, 2010). The injection age of the quartz vein has been estimated at ca. 127 Ma (Early Cretaceous) based on the sericite K–Ar age of the altered host rock (So et al., 1988).

3. Zircon U–Pb Age Dating

3.1. Analytical Method

We conducted LA-ICP-MS zircon U–Pb analysis for four samples from the rhyolitic tuff (CY114), tuffaceous sedimentary rocks (CY146, CY154), and metapsammite (CY011). The location of each sample is indicated in Figure 2. Zircons were extracted using a heavy liquid technique and then mounted on epoxy disks with reference zircons. Internal textures were observed using cathodoluminescence (CL) and backscattered electron (BSE) images (Fig. 9). LA-ICP-MS zircon U–Pb dating was conducted using an Agilent 7900 ICP-MS instrument combined with a GeoLas HD laser ablation system at the WuhanSampleSolution Analytical Technology Co., Ltd., Wuhan, China. The measurement conditions were as follows: 32 µm diameters of spot size, 5 Hz repetition rate, and laser energy of 80 mJ. All uncertainties of the analytical results are 1σ levels.

Figure 9. Scanning electron microscope cathodoluminescence (SEM-CL) images of sectioned zircon grains from the rhyolitic tuff, metapsammite, and tuffaceous sandstone.

The analyzed data were processed using the ISOPLOT software (Ludwig, 2008). Age probability curves were plotted using 206Pb/238U ages for <1000 Ma samples and 207Pb/206Pb ages for >1000 Ma, with a discordance of < ±10%. The discordance (%) of the zircon U-Pb isotopic age data were calculated as [1-(206Pb/238U age)/(207Pb/235U age)] * 100 and [1-(206Pb/238U age)/(207Pb/206Pb age)] * 100 for ages younger and older than 1000 Ma, respectively.

3.2. Result

3.2.1. Rhyolitic tuff

The zircons from the rhyolitic tuff sample (CY114) occur as stubby to prismatic (aspect ratio of 1.2–3), and the grain size ranges from 50–130 µm in length (Fig. 9). Almost every grain shows marked oscillatory zoning, which is a common feature of igneous zircons. In addition, some grains show local intermediate resorption, and a few grains include chaotic inherited core. The Th/U ratio is in the range of 0.28–1.32, probably indicating the igneous origin of the zircons (Table 1) (Hoskin and Black, 2000). The zircon U–Pb data is shown in the Terra–Wasserburg concordia diagram (Fig. 10a). It yields a weighted mean 206Pb/238U age of 169.19±1.1 Ma (MSDW=0.57), which

Table 1 . LA-ICP-MS U-Pb isotopic data of zircon grains from rhyolitic tuff in the study area

Sample nameU (ppm)Th/UIsotopic ratiosApparent age (Ma)
207Pb/206Pb207Pb/235U206Pb/238U207Pb/206Pb207Pb/235U206Pb/238UDisc.
CY114 Rhyolitic tuff (Location, WGS 84; 36.52473N, 126.86868E)
CY114-52.12110.790.04750.00310.16400.00980.02520.000476.0144.42154.28.5582160.42.8-4.0%
CY114-56.16120.490.05090.00220.18010.00770.02550.0003235.399.99168.26.6433162.22.13.6%
CY114-59.12070.830.05400.00360.18870.01140.02570.0004368.6154.61175.69.7521163.32.77.0%
CY114-38.12890.780.04760.00240.16930.00890.02570.000479.7118.51158.87.7097163.92.4-3.2%
CY114-29.12670.520.05390.00290.19150.01000.02580.0004364.9124.06177.98.4811164.12.47.8%
CY114-69.11990.600.05190.00370.18370.01240.02580.0005283.4164.79171.210.6375164.43.04.0%
CY114-50.16220.710.05010.00210.17900.00720.02590.0004211.296.28167.26.1978165.12.21.3%
CY114-70.14100.630.05380.00300.19410.01060.02600.0004361.2125.91180.19.0089165.42.58.1%
CY114-62.14850.580.05120.00250.18430.00890.02600.0004255.6117.6171.77.6460165.52.33.7%
CY114-54.17850.400.04980.00200.18030.00710.02610.0003183.492.58168.36.1368166.32.11.2%
CY114-12.14500.390.04700.00190.16980.00690.02620.000455.790.73159.36.0324166.52.4-4.5%
CY114-63.17040.410.05210.00220.18890.00770.02620.0004300.196.28175.76.5884166.62.35.2%
CY114-10.16980.390.05170.00200.18970.00770.02630.0003272.388.88176.36.5535167.22.15.2%
CY114-04.12890.800.05420.00300.19650.01070.02630.0004388.9122.21182.19.1013167.22.68.2%
CY114-39.12830.410.05360.00270.19500.01000.02630.0004353.8114.81180.98.5122167.52.47.4%
CY114-15.114610.600.05190.00160.19040.00600.02640.0003283.468.51177.05.1570167.81.95.2%
CY114-48.12970.700.05070.00270.18440.00880.02640.0004227.8122.21171.97.5681167.82.42.4%
CY114-19.14580.460.05200.00220.19060.00800.02640.0003283.4100.91177.16.7934167.82.15.2%
CY114-27.13990.510.05230.00230.19110.00840.02650.0004298.299.99177.57.1298168.32.35.2%
CY114-64.12480.660.04880.00330.17530.01120.02650.0005200.199.99164.09.6826168.43.0-2.7%
CY114-49.13480.510.05190.00270.19040.01020.02650.0004279.7115.73177.08.7196168.52.54.8%
CY114-20.12771.080.05260.00260.19100.00920.02650.0004322.3112.95177.57.8699168.72.84.9%
CY114-16.18660.330.05260.00200.19410.00780.02650.0003309.388.88180.16.6093168.82.06.3%
CY114-46.14170.700.04910.00250.17970.00900.02660.0004153.8150.91167.87.7199169.22.6-0.8%
CY114-11.16010.300.04620.00230.17050.00690.02660.00045.7118.51159.96.0274169.32.4-5.9%
CY114-28.17900.600.05220.00160.19280.00630.02660.0004294.572.22179.05.3558169.42.25.4%
CY114-02.11920.800.05440.00380.19780.01290.02660.0005387.1183.31183.310.9397169.42.97.5%
CY114-33.19940.390.05260.00180.19490.00650.02670.0003322.377.77180.85.5354170.02.06.0%
CY114-30.14221.140.05110.00220.18770.00780.02680.0004242.7101.84174.76.6818170.22.32.6%
CY114-01.17040.710.05020.00180.18600.00670.02680.0004211.281.47173.25.7441170.52.31.6%
CY114-58.12410.690.05090.00320.18650.01080.02680.0005235.3146.28173.69.2246170.53.01.8%
CY114-40.16800.530.05010.00210.18510.00770.02680.0003211.298.13172.46.5971170.52.11.1%
CY114-05.110760.280.05100.00150.18920.00560.02680.0003239.068.51176.04.7536170.62.03.0%
CY114-07.12330.740.04940.00270.18150.00930.02680.0005164.9134.24169.38.0139170.82.9-0.9%
CY114-17.110541.320.04860.00150.18160.00570.02690.0003127.972.22169.44.9040170.81.8-0.8%
CY114-61.116490.570.05220.00150.19410.00550.02690.0003294.563.88180.14.6830170.92.05.1%
CY114-22.14461.140.04680.00270.17410.01000.02690.000539.0133.32163.08.6682171.22.8-5.0%
CY114-23.15551.190.05350.00410.20320.01620.02700.0003350.1176.83187.813.6828171.92.28.5%
CY114-09.13200.740.05020.00250.18870.00940.02710.0004205.6116.65175.68.0219172.12.41.9%
CY114-08.13260.720.04930.00300.18480.01010.02720.0004161.2142.58172.28.6738172.82.7-0.3%
CY114-31.16880.540.04820.00170.18110.00630.02720.0003109.478.70169.05.4546172.82.0-2.3%
CY114-47.13380.580.05480.00250.20520.00950.02720.0004405.6103.69189.68.0092173.02.68.7%
CY114-41.12920.690.05240.00290.19940.01130.02730.0004301.9127.76184.69.5888173.62.66.0%
CY114-44.16050.350.05270.00230.20060.00820.02740.0004322.398.14185.66.9098174.02.56.2%
CY114-13.11880.670.04750.00320.17910.01200.02740.000572.3161.09167.310.3304174.23.2-4.1%
CY114-03.12760.440.05190.00280.19620.01040.02750.0005279.7124.06181.98.8210174.72.93.9%
CY114-32.15500.460.05060.00200.19370.00800.02750.0004233.497.21179.76.8267174.82.52.8%
CY114-57.12610.790.05550.00350.21020.01220.02760.0004435.2140.73193.710.2185175.72.59.3%
CY114-36.13000.470.05410.00270.20520.01020.02770.0004376.0114.81189.58.5767176.32.77.0%
CY114-35.11570.580.05540.00470.20390.01370.02800.0006427.8188.87188.411.5610178.03.95.5%
CY114-18.15870.580.05530.00220.26770.01030.03490.0004433.495.36240.98.2630221.22.88.2%

Figure 10. (a) Concordia diagram of the zircon U-Pb ages from the rhyolitic tuff. Ages with a discordance of < ±10% are used for plotting in the diagram. Plots with a discordance of < ±5% are colored in red. (b) Probability–density plots and histograms of detrital zircon U–Pb ages of the tuffaceous sedimentary rocks and metapsammite.

likely indicates the timing of volcanism.

3.2.2. Tuffaceous sedimentary rocks and metapsammite

Of the total 260 detrital zircon grains from the tuffaceous sedimentary rocks and metapsammite, 90 grains show acceptable discordance. In particular, the metapsammite sample CY011 has only 12 concordant data, which is insufficient to constrain the depositional age of the protolith. Most zircon grains show oscillatory zoning except for some Precambrian zircon grains. The Th/U ratios of the detrital zircon grains with acceptable discordance are mostly above 0.1, likely indicating the igneous origin. The zircon U–Pb age distributions of the tuffaceous sedimentary rock and metapsammite are represented in the probability-density plot (Fig. 10b). The detailed zircon U–Pb isotopic data are shown in Tables 2, 3.

Table 2 . LA-ICP-MS U-Pb isotopic data of detrital zircon grains from metapsammite in the study area

Sample nameU (ppm)Th/UIsotopic ratiosApparent age (Ma)
207Pb/206Pb207Pb/235U206Pb/238U207Pb/206Pb207Pb/235U206Pb/238UDisc.
CY011 Metapsammite (Location, WGS 84; 36.517764N, 126.876687E)
CY011-40.17300.010.05540.00220.25980.01030.03390.0005427.886.1234.58.3214.73.28.4%
CY011-11.110600.200.12060.00272.08850.05320.12410.00191964.539.21145.017.5753.910.834.2%
CY011-1.118010.140.10440.00252.29070.05700.15780.00211705.644.41209.417.6944.511.621.9%
CY011-56.18180.180.12930.00303.13280.07610.17470.00222088.641.41440.818.71038.012.350.3%
CY011-58.113850.210.12570.00273.19980.08650.18350.00362038.938.31457.120.91085.919.646.7%
CY011-7.16690.090.16130.00394.25800.14350.18810.00502468.840.41685.327.71111.326.955.0%
CY011-8.14420.070.11110.00242.94750.06510.19030.00251817.040.31394.216.81123.113.338.2%
CY011-43.17040.150.11720.00263.10780.08720.19060.00381914.538.71434.621.61124.620.641.3%
CY011-54.14240.120.12730.00323.57160.14330.19970.00582061.145.51543.231.81173.930.943.0%
CY011-26.15330.170.12240.00253.63770.09180.21350.00341991.730.61557.820.11247.618.137.4%
CY011-66.114220.030.12180.00333.87560.17800.22280.00661983.043.51608.637.11296.634.934.6%
CY011-9.14270.600.13470.00284.26100.09240.22720.00332160.835.81685.917.91319.717.238.9%
CY011-45.14990.180.13010.00294.19500.10400.23130.00292099.137.81673.020.41341.515.436.1%
CY011-13.17700.290.12920.00304.17660.10260.23240.00282087.336.31669.420.21347.214.835.5%
CY011-33.16750.100.12190.00234.24850.08320.25070.00321984.333.01683.416.11441.816.427.3%
CY011-69.15410.200.12530.00254.41440.12720.25250.00512033.035.01715.023.91451.626.228.6%
CY011-59.18430.180.15030.00305.29380.12210.25340.00342349.733.21867.919.71456.117.338.0%
CY011-27.16110.120.11680.00214.12060.08420.25390.00311909.332.31658.416.71458.316.023.6%
CY011-25.16280.240.16160.00355.83340.13450.26040.00332472.536.61951.420.01491.817.039.7%
CY011-3.115030.180.14350.00295.27980.12330.26380.00392270.135.01865.620.01509.320.233.5%
CY011-63.13770.880.14510.00305.41320.11570.26950.00402288.635.31886.918.41538.520.432.8%
CY011-47.110660.740.15580.00386.05760.14320.28070.00372410.241.01984.220.61594.918.533.8%
CY011-51.13840.110.11880.00244.63380.09150.28140.00291938.937.01755.416.51598.514.517.6%
CY011-14.112360.490.13360.00275.31180.11020.28650.00322146.635.51870.817.81623.916.324.3%
CY011-12.15680.620.12810.00305.13690.12120.28800.00302071.940.61842.220.11631.615.021.3%
CY011-50.16670.010.11390.00254.58870.10170.29030.00331862.039.81747.218.51643.016.511.8%
CY011-10.110570.610.13040.00255.29140.11400.29100.00402102.833.01867.518.41646.620.221.7%
CY011-24.15470.530.12430.00265.02820.10560.29200.00302020.436.01824.117.81651.715.018.2%
CY011-53.16340.240.14110.00295.80960.14910.29600.00502242.635.51947.822.31671.324.925.5%
CY011-36.16850.740.12940.00285.40210.11900.30080.00402100.038.11885.218.91695.119.619.3%
CY011-55.14200.820.15380.00376.43960.17990.30130.00492388.641.42037.724.61697.724.528.9%
CY011-30.15150.410.15110.00346.33810.13490.30190.00332358.338.92023.718.71700.616.227.9%
CY011-52.15260.450.12200.00255.11230.10070.30230.00301987.036.01838.116.81702.614.914.3%
CY011-32.14000.460.14290.00306.14390.16410.30710.00522264.835.61996.523.41726.425.723.8%
CY011-68.16280.180.12350.00275.32850.12160.31150.00462009.343.41873.519.61748.122.513.0%
CY011-44.13510.390.12960.00285.65990.12940.31470.00452094.438.11925.319.81763.622.115.8%
CY011-61.12330.270.13990.00356.17260.13340.31940.00402225.643.82000.618.91786.919.819.7%
CY011-20.110310.040.14810.00306.66670.14460.32560.00392323.835.22068.219.21817.019.021.8%
CY011-19.14500.300.13270.00326.04640.17110.32880.00572200.042.11982.524.71832.627.616.7%
CY011-64.13320.350.16240.00347.39700.17640.32950.00592480.630.12160.621.41835.928.526.0%
CY011-22.15190.460.15310.00307.03060.21360.33010.00732380.633.02115.327.01839.035.622.8%
CY011-57.15710.460.13570.00296.22340.13990.33050.00412173.236.42007.719.71841.020.115.3%
CY011-67.15860.600.14430.00356.64270.15570.33190.00402279.340.62065.020.71847.519.218.9%
CY011-39.16660.370.12860.00265.96860.12510.33420.00382079.337.21971.318.31858.518.310.6%
CY011-15.17420.420.12770.00255.96570.12730.33660.00402066.435.21970.918.61870.519.49.5%
CY011-70.15180.210.12760.00255.97680.13080.33820.00482065.735.21972.519.11877.823.19.1%
CY011-37.13670.510.12970.00306.09240.13920.33850.00412094.840.61989.220.01879.619.810.3%
CY011-62.11330.600.16120.00427.58070.20880.33960.00612468.243.52182.624.71884.929.323.6%
CY011-42.17960.270.15190.00297.24090.13740.34390.00392368.527.62141.617.01905.518.619.6%
CY011-46.12791.020.15200.00357.45910.18410.35310.00472368.239.52168.122.11949.422.217.7%
CY011-28.15470.540.14280.00267.09770.15780.35750.00572260.831.52123.819.81970.326.912.9%
CY011-65.17060.390.15550.00337.73520.18310.35860.00562407.135.02200.721.31975.626.817.9%
CY011-49.13890.400.15500.00407.75450.19350.36090.00472401.549.22202.922.51986.622.217.3%
CY011-6.14800.420.12930.00306.63450.15790.36700.00502100.040.72064.021.02015.023.54.0%
CY011-5.112300.450.16930.00358.73850.18950.36990.00492550.934.12311.119.82028.823.220.5%
CY011-23.13461.380.16290.00338.52420.21640.37830.00722486.132.92288.523.12068.533.816.8%
CY011-35.15220.310.14740.00297.88030.19690.38410.00712316.433.52217.422.62095.433.29.5%
CY011-16.12800.510.13280.00287.25330.16050.39460.00512134.937.22143.119.82144.023.6-0.4%
CY011-31.17590.320.14800.00328.20790.16890.39830.00432324.136.02254.218.72161.220.07.0%
CY011-21.14670.250.15830.00328.78530.21870.40080.00672438.934.42316.022.82172.630.910.9%
CY011-48.14911.070.16100.00418.99100.23660.40190.00532466.438.12337.124.12177.824.211.7%
CY011-60.14140.650.16470.00329.37200.18750.41080.00472505.632.42375.118.42218.421.311.5%
CY011-2.13030.340.14020.00318.23010.21410.42150.00722229.371.52256.723.62267.132.8-1.7%
CY011-4.11180.420.15470.00369.30700.21780.43190.00522398.540.32368.721.52314.223.33.5%
CY011-41.11760.670.16260.00339.83510.20030.43630.00502483.034.62419.418.82334.022.66.0%
CY011-17.12130.710.16340.00369.89010.21010.43850.00502491.137.22424.619.72343.822.45.9%
CY011-34.11740.530.23630.004418.34740.38480.55760.00723095.429.63008.120.32856.530.07.7%

Table 3 . LA-ICP-MS U-Pb isotopic data of detrital zircon grains from tuffaceous sedimentary rock in the study area

Sample nameU (ppm)Th/UIsotopic ratiosApparent age (Ma)
207Pb/206Pb207Pb/235U206Pb/238U207Pb/206Pb207Pb/235U206Pb/238UDisc.
CY146 Tuffaceous sedimentary rock (Location, WGS 84; 36.52387N, 126.86057E)
CY146-63.18350.320.04900.00170.17920.00590.02650.0004150.175.0167.45.1168.52.4-0.6%
CY146-81.12390.610.06010.00300.21800.01000.02660.0005605.6107.4200.28.3169.32.915.5%
CY146-15.11210.440.04690.00500.17150.01700.02670.000642.7237.0160.714.7169.83.7-5.6%
CY146-55.12790.560.05020.00350.18430.01200.02680.0004211.2165.7171.810.3170.42.70.8%
CY146-41.1560.650.06810.00720.25290.02140.02700.0007872.2222.7228.917.3171.84.425.0%
CY146-84.12400.430.05380.00300.19820.01010.02710.0005361.2125.9183.68.6172.63.06.0%
CY146-44.12061.310.07460.00550.27620.01850.02720.00051057.4147.8247.614.7172.82.930.2%
CY146-11.14870.430.04930.00230.18590.00810.02740.0004161.2107.4173.26.9174.42.3-0.7%
CY146-96.11990.780.08800.00590.32660.02010.02750.00051383.3129.2286.915.4174.63.239.2%
CY146-20.11861.080.05140.00330.19510.01140.02770.0005257.5146.3181.09.7176.13.02.7%
CY146-93.13270.730.05230.00250.21840.01010.03040.0005301.9107.4200.68.4193.13.03.7%
CY146-26.12790.500.06960.00310.34090.01790.03510.0010916.792.6297.813.5222.66.125.3%
CY146-92.11310.700.08820.00660.43590.03170.03600.00071387.0144.0367.422.4227.84.238.0%
CY146-71.12400.450.04970.00260.25970.01280.03800.0005189.0122.2234.410.3240.73.3-2.7%
CY146-88.12310.470.06260.00340.34160.01840.03970.0006694.5115.6298.413.9251.23.815.8%
CY146-36.12910.400.04970.00230.28960.01340.04240.0006189.0111.1258.310.5268.03.9-3.8%
CY146-45.11920.360.05170.00290.30410.01710.04260.0007272.3125.9269.613.3269.14.40.2%
CY146-39.18740.020.05230.00170.31200.01040.04300.0005298.275.9275.88.0271.63.01.5%
CY146-24.121820.010.10830.00222.14910.04540.14280.00151772.23.21164.814.7860.38.526.1%
CY146-67.17410.020.10880.00212.98300.05720.19730.00201779.936.61403.314.61160.710.634.8%
CY146-23.113420.080.11190.00283.08470.07760.19860.00241831.545.71428.919.31168.012.836.2%
CY146-69.15910.070.11760.00253.47430.08010.21240.00281920.737.51521.418.21241.915.035.3%
CY146-75.19560.010.10920.00223.66410.09260.24050.00421787.041.71563.620.21389.322.122.3%
CY146-57.15250.060.11730.00244.10710.08360.25140.00271916.736.01655.716.71445.714.124.6%
CY146-34.110010.030.14970.00345.24510.13450.25170.00352342.338.31860.021.91447.318.238.2%
CY146-37.13370.160.11530.00264.25240.09740.26610.00311884.940.71684.218.91521.115.619.3%
CY146-74.15400.120.11900.00244.41160.08720.26630.00261942.635.31714.516.41522.013.221.7%
CY146-06.16900.060.11340.00254.22920.09590.26830.00361854.040.01679.718.71532.118.417.4%
CY146-60.14390.070.11670.00244.37870.10170.26920.00401905.936.61708.319.21536.720.619.4%
CY146-04.19050.180.14540.00325.47940.12220.27080.00312294.438.41897.419.21545.015.832.7%
CY146-59.18150.050.12040.00274.64620.13980.27470.00521962.072.41757.625.21564.426.220.3%
CY146-62.16610.050.11150.00214.42510.09130.28520.00401833.333.31717.017.11617.520.311.8%
CY146-70.19610.010.11080.00244.40720.09370.28630.00311813.038.91713.717.61623.115.710.5%
CY146-100.17150.010.13060.00295.19620.12420.28660.00402105.940.31852.020.41624.620.022.9%
CY146-79.14710.140.11090.00224.44410.08920.28820.00351814.536.71720.616.71632.417.410.0%
CY146-68.17730.430.12640.00245.09750.09730.29000.00272050.034.41835.716.21641.513.519.9%
CY146-09.15260.060.11350.00224.60600.09280.29190.00361857.434.61750.416.91650.918.011.1%
CY146-77.110360.000.11390.00254.66470.10500.29360.00351862.740.11760.918.91659.517.410.9%
CY146-66.18280.000.11580.00224.72970.09200.29370.00321892.335.21772.516.31660.216.212.3%
CY146-31.110030.010.11530.00214.75670.08750.29700.00301887.031.61777.315.51676.414.711.2%
CY146-43.15810.040.12120.00255.02220.12480.29710.00461973.837.01823.121.11677.122.815.0%
CY146-50.11850.500.11360.00264.70570.10180.29910.00341857.140.71768.318.21687.116.89.2%
CY146-47.114620.040.11830.00254.97750.11430.30390.00451931.538.11815.519.51710.522.111.4%
CY146-95.19430.220.12980.00365.56290.16400.30830.00452096.049.11910.425.41732.522.217.3%
CY146-01.118961.910.11740.00225.05880.09590.31020.00341917.033.81829.216.11741.916.89.1%
CY146-54.17760.540.13080.00245.65640.10220.31070.00352109.633.21924.715.61744.217.417.3%
CY146-61.14530.130.11020.00214.76330.08900.31090.00381802.233.81778.415.71745.318.63.2%
CY146-38.18220.100.12820.00295.63280.15600.31510.00452073.840.41921.123.91765.721.914.9%
CY146-12.19310.060.11590.00225.09650.09200.31610.00281894.833.51835.515.41770.813.96.5%
CY146-53.14650.210.12120.00255.35770.10440.31780.00361973.835.31878.116.71779.217.79.9%
CY146-76.120600.690.12400.00275.49680.12010.31820.00372014.538.91900.118.81781.018.311.6%
CY146-35.16820.400.12440.00305.54690.13950.32120.00402020.142.91907.921.71795.719.511.1%
CY146-56.16260.380.11410.00215.12980.09150.32310.00351866.433.31841.115.21804.917.13.3%
CY146-03.16860.530.12450.00245.60430.11140.32340.00332021.335.21916.817.21806.515.910.6%
CY146-08.17460.150.13580.00276.14890.11780.32570.00342175.934.71997.216.81817.416.516.5%
CY146-29.17350.190.13930.00346.48770.24680.32850.00742220.442.32044.233.51831.236.017.5%
CY146-80.15970.130.11490.00215.28710.09880.33050.00361877.527.31866.816.01840.817.32.0%
CY146-28.14940.200.13200.00296.09950.15730.33170.00462124.438.91990.222.51846.422.413.1%
CY146-07.1490.590.11330.00385.20510.16480.33290.00481853.765.01853.427.01852.523.40.1%
CY146-91.13380.290.14530.00336.71840.16860.33320.00472291.140.02075.022.21853.822.819.1%
CY146-85.15720.190.14500.00296.73220.14230.33400.00382288.034.12076.918.71857.618.418.8%
CY146-32.13700.100.13080.00256.06090.11630.33410.00352109.033.21984.616.81858.317.111.9%
CY146-25.14540.410.12910.00246.02340.11230.33630.00322087.032.31979.216.31868.615.610.5%
CY146-94.13810.250.13190.00386.15510.18020.33660.00492123.850.01998.125.61870.523.811.9%
CY146-42.14980.130.13250.00316.28210.19390.33720.00592131.836.32016.027.11873.328.312.1%
CY146-73.13750.470.12620.00265.96110.12050.33980.00362055.637.21970.217.61885.717.28.3%
CY146-18.15660.640.12870.00256.10600.12360.34120.00372080.629.21991.117.71892.218.09.1%
CY146-64.15290.070.13750.00296.55120.13960.34240.00402195.436.72052.818.81898.019.413.5%
CY146-83.111660.460.14310.00296.91910.14010.34770.00402265.734.12101.118.01923.419.015.1%
CY146-52.18050.060.14450.00287.11890.13830.35430.00422283.334.42126.417.41955.120.214.4%
CY146-46.16680.020.14300.00317.04460.16340.35510.00452264.837.02117.120.71958.821.413.5%
CY146-65.14110.270.13650.00306.84350.15010.36030.00422183.037.22091.419.51983.520.19.1%
CY146-98.112860.100.16730.00398.37770.19740.36130.00472531.239.22272.821.41988.322.321.4%
CY146-17.16660.250.13600.00286.92400.14640.36640.00442177.536.42101.718.82012.220.97.6%
CY146-13.14250.240.13300.00296.87080.20020.36790.00612138.938.32094.925.92019.528.95.6%
CY146-87.17450.250.15210.00327.85060.18200.37100.00442370.136.42214.020.92034.120.614.2%
CY146-99.18070.570.16250.00378.36300.18460.37140.00442483.338.32271.220.12036.120.518.0%
CY146-27.116200.160.14950.00287.74360.15310.37320.00432340.432.72201.717.82044.320.212.7%
CY146-40.13480.110.13350.00297.01240.24160.37320.00792146.338.32113.030.72044.537.04.7%
CY146-49.16380.040.18570.004010.05300.29490.38500.00572705.635.52439.727.12099.626.722.4%
CY146-21.17940.240.15700.00328.39300.16980.38500.00402423.833.22274.418.42099.718.813.4%
CY146-97.12250.950.14340.00377.71870.20240.38790.00492268.849.22198.823.62113.022.86.9%
CY146-58.1960.660.13450.00357.44280.18070.39870.00482157.740.02166.121.82163.122.4-0.3%
CY146-72.13550.190.14360.00288.01850.15510.40170.00422272.234.42233.117.52176.919.24.2%
CY146-16.13270.330.18290.004710.28590.25180.40480.00462679.942.32460.822.72191.021.018.2%
CY146-19.14960.560.14990.00288.44340.14630.40570.00372346.331.22279.915.82195.517.26.4%
CY146-05.13190.340.12830.00307.27410.19720.40630.00642075.941.72145.624.22198.029.4-5.9%
CY146-89.13520.330.15460.00398.86250.23170.41320.00542398.242.62323.923.92229.724.67.0%
CY146-48.16170.020.15130.00298.77340.17630.41790.00492360.833.22314.718.42251.122.14.6%
CY146-14.15430.610.15590.00319.13630.18120.42180.00472413.039.02351.718.22268.521.36.0%
CY146-02.13670.850.15750.00329.27570.17780.42450.00442428.734.32365.617.62281.120.06.1%
CY146-86.11770.770.15830.00349.39730.20680.42750.00482438.936.12377.620.32294.421.85.9%
CY146-22.16510.630.16330.00359.71210.21060.42800.00452490.436.92407.920.02296.820.27.8%
CY146-30.12691.160.15870.00339.48680.19620.43110.00472442.335.52386.319.12310.921.05.4%
CY146-78.11600.630.15740.00349.50480.20200.43380.00502428.136.12388.019.62322.622.64.3%
CY146-10.12010.530.15380.00309.69890.21910.45250.00622390.733.32406.620.92406.227.7-0.6%
CY146-33.15560.260.16730.003210.76440.21540.46380.00522531.532.42503.018.72456.223.13.0%
CY154 Tuffaceous sedimentary rock (Location, WGS 84; 36.51727N, 126.85756E)
CY154-27.15960.600.06440.00280.21710.00950.02430.0004766.797.2199.57.9155.12.422.3%
CY154-60.11800.430.06450.00430.21660.01380.02480.0005766.7141.5199.111.5158.13.020.6%
CY154-74.15480.560.05850.00270.20260.00900.02510.0003546.3106.5187.37.6159.82.014.7%
CY154-52.13540.450.05230.00470.18260.01630.02530.0004298.2209.2170.314.0160.82.55.6%
CY154-04.16750.660.05750.00260.20110.00870.02550.0004522.3100.0186.17.4162.02.812.9%
CY154-02.19350.420.04930.00200.17350.00680.02550.0003164.988.0162.55.9162.21.90.1%
CY154-80.11750.490.05180.00410.17510.01200.02560.0005276.0184.2163.810.4162.83.20.6%
CY154-66.12950.400.06490.00750.23240.02570.02560.0005772.2244.4212.221.1163.13.123.1%
CY154-47.11460.510.04830.01460.16350.04400.02570.0006122.3583.3153.738.4163.73.8-6.5%
CY154-53.15000.550.05360.00240.19080.00860.02580.0003353.8101.8177.37.3164.42.07.3%
CY154-34.13650.570.05220.00260.18770.00900.02610.0004294.5145.4174.77.7166.32.64.8%
CY154-45.14720.530.05100.00320.18590.01220.02630.0004242.7150.9173.210.5167.22.23.5%
CY154-77.1990.850.07510.00610.26390.01830.02630.00071072.2166.8237.814.7167.34.429.6%
CY154-44.12710.400.06780.00490.24290.01730.02660.0005861.1150.0220.814.1169.23.123.4%
CY154-18.13150.360.04840.00250.17720.00920.02660.0005120.5114.8165.68.0169.32.9-2.2%
CY154-62.12600.510.04960.00340.18010.01140.02660.0004189.0157.4168.19.8169.52.6-0.8%
CY154-23.12550.720.04800.00350.17740.01270.02670.000598.2162.9165.811.0170.13.1-2.6%
CY154-86.11420.640.05450.00460.19980.01670.02680.0006394.5188.9184.914.1170.53.87.8%
CY154-48.1780.340.09650.01610.35980.05830.02700.00071566.7318.5312.043.6171.64.745.0%
CY154-54.12550.470.05460.00280.20310.01020.02710.0004398.2116.7187.88.6172.12.58.3%
CY154-12.16430.850.04820.00200.18140.00760.02710.0004109.498.1169.36.5172.12.2-1.7%
CY154-58.12190.460.05520.00400.20580.01460.02710.0005420.4161.1190.012.3172.43.19.3%
CY154-01.13630.500.05180.00250.19530.00980.02720.0004276.0108.3181.18.3173.22.74.4%
CY154-55.13150.440.05930.00310.22760.01210.02780.0005576.0111.9208.210.0177.02.915.0%
CY154-83.13000.890.05160.00290.25170.01290.03560.0006333.495.4228.010.5225.53.51.1%
CY154-19.11380.630.05130.00350.27580.01760.03900.0007253.8183.3247.314.0246.94.40.2%
CY154-24.13140.040.05400.00290.30470.01680.04110.0010372.3122.2270.113.0259.96.43.8%
CY154-71.17910.540.05780.00180.46800.01410.05820.0006520.468.5389.89.8364.43.66.5%
CY154-14.18770.410.06040.00150.59470.01590.07060.0009620.453.7473.910.1439.95.37.2%
CY154-33.18270.020.09210.00221.29690.03010.10150.00111470.145.1844.413.3623.46.426.2%
CY154-30.16280.370.09200.00231.63450.04160.12800.00161533.348.1983.616.0776.69.421.0%
CY154-97.15790.270.09730.00271.77920.07210.13090.00331572.257.61037.926.4792.818.723.6%
CY154-17.11200.660.07310.00261.42420.05200.14030.00171016.772.2899.121.8846.69.85.8%
CY154-03.1860.870.06500.00251.25840.04710.14060.0018773.875.8827.221.2848.310.4-2.5%
CY154-57.16770.110.11190.00242.24910.05030.14500.00171831.538.31196.515.7872.89.527.1%
CY154-69.15140.110.11240.00262.27030.04920.14550.00171838.942.11203.115.3875.59.627.2%
CY154-72.110610.020.11850.00322.44580.06400.14790.00161944.548.11256.218.9889.49.329.2%
CY154-98.18850.030.11230.00262.45860.06220.15820.00211836.742.71260.018.3946.711.624.9%
CY154-73.13490.140.10470.00292.30920.06430.15840.00191709.351.91215.119.7948.010.822.0%
CY154-51.17110.020.10710.00222.44810.05510.16450.00201751.537.71256.916.3982.010.921.9%
CY154-84.116490.010.10690.00262.44740.05930.16510.00241746.644.41256.617.5985.013.021.6%
CY154-11.16050.450.13820.00293.72570.07990.19390.00242205.235.81576.917.21142.513.148.2%
CY154-41.19950.260.08310.00212.27880.06090.19800.00251272.249.21205.718.91164.713.38.5%
CY154-10.17100.040.11290.00233.13810.07510.19920.00261847.236.71442.118.51171.014.036.6%
CY154-81.14980.730.12880.00283.59620.08430.20120.00262083.338.71548.718.71182.014.043.3%
CY154-25.17160.130.10930.00333.12270.09790.20470.00341787.455.11438.324.11200.718.332.8%
CY154-87.16950.150.11540.00243.35280.06630.20930.00201887.037.01493.415.51224.910.935.1%
CY154-16.15740.110.11910.00243.63150.07270.21970.00231942.940.91556.516.01280.212.334.1%
CY154-92.15131.170.08950.00202.74670.06040.22160.00221414.542.61341.216.41290.511.78.8%
CY154-56.16230.080.12050.00273.85780.10970.22990.00421964.839.41604.923.01333.821.932.1%
CY154-38.15810.110.10770.00233.49230.14550.23120.00811761.139.51525.532.91341.042.423.9%
CY154-59.13090.690.14650.00304.85100.09830.23930.00262305.235.21793.817.11383.313.740.0%
CY154-65.16170.060.12420.00274.15670.08540.24080.00242018.239.01665.516.91391.012.431.1%
CY154-68.17450.140.11520.00253.97350.08790.24740.00261883.339.51628.818.01424.913.724.3%
CY154-09.18150.160.10840.00203.87990.07670.25740.00291773.233.61609.516.01476.715.016.7%
CY154-61.15850.010.11780.00294.21500.12340.25790.00461924.145.51677.024.11478.923.623.1%
CY154-91.13680.090.12160.00304.42170.10890.26210.00301979.948.61716.420.41500.615.524.2%
CY154-89.13700.130.13240.00304.87250.11450.26480.00292131.535.01797.519.81514.514.728.9%
CY154-79.14180.330.14050.00385.19380.14800.26640.00322235.246.81851.624.31522.316.431.9%
CY154-67.18210.190.12420.00304.67900.19290.26830.00882017.643.71763.534.51532.244.824.1%
CY154-07.15070.110.12110.00284.64900.11300.27640.00321972.540.61758.120.31573.516.220.2%
CY154-75.11540.740.14660.00365.66520.14870.27750.00352306.542.61926.122.71578.917.531.5%
CY154-78.19880.130.11930.00304.68980.11690.28400.00301946.345.81765.420.91611.314.917.2%
CY154-64.14090.300.14970.00315.94270.12590.28570.00312342.941.21967.518.51619.915.630.9%
CY154-21.15530.020.11580.00274.68570.10980.29110.00321892.347.21764.719.61647.115.813.0%
CY154-88.19300.200.14860.00306.10000.21370.29150.00752331.535.01990.330.61649.137.629.3%
CY154-08.17490.020.11400.00224.70140.09130.29720.00301864.835.21767.516.31677.615.010.0%
CY154-39.17150.030.11680.00254.92920.10450.30440.00341909.338.41807.317.91713.117.010.3%
CY154-42.17320.300.13620.00375.78450.20060.30600.00642188.948.11944.130.11720.831.421.4%
CY154-22.14950.230.13600.00345.91050.15100.31240.00412176.943.81962.822.21752.520.319.5%
CY154-99.14840.210.14130.00316.16760.16200.31420.00402243.537.81999.923.01761.219.721.5%
CY154-37.12620.520.12830.00305.60320.13540.31460.00452075.941.01916.620.91763.122.015.1%
CY154-40.111980.320.11540.00255.09080.11270.31870.00341887.034.41834.618.81783.216.95.5%
CY154-26.14950.190.11400.00305.17380.13780.32610.00431864.848.21848.322.71819.621.22.4%
CY154-94.13500.220.15720.00347.19390.22170.32800.00692427.835.62135.727.51828.533.724.7%
CY154-36.13960.110.11090.00255.10560.11490.33080.00401816.740.71837.019.21842.119.4-1.4%
CY154-50.11590.500.16130.00367.39140.16980.33100.00442470.138.02159.920.61843.021.225.4%
CY154-100.15040.330.14940.00306.99880.14410.33870.00322339.233.82111.318.31880.415.319.6%
CY154-82.13860.470.15270.00327.26000.15600.34200.00342376.236.32143.919.21896.316.220.2%
CY154-95.14440.050.13340.00306.50410.20570.34930.00652142.940.32046.527.91931.331.39.9%
CY154-93.14010.110.13630.00286.62090.13390.35040.00312180.635.22062.117.91936.715.011.2%
CY154-43.14600.580.14350.00447.07380.22600.35790.00562270.152.82120.728.51972.226.513.1%
CY154-35.14210.310.14290.00287.15260.14160.35980.00392262.033.62130.617.71981.218.412.4%
CY154-06.11820.430.14510.00347.39220.17120.36870.00452288.640.42160.020.82023.221.011.6%
CY154-29.13020.460.17310.00388.91370.20470.37080.00472587.437.02329.221.02033.122.021.4%
CY154-96.15880.250.14810.00357.92850.21310.38560.00532324.440.62222.924.32102.324.89.6%
CY154-90.12690.180.16880.00399.32060.25360.39690.00642546.338.92370.025.02154.829.815.4%
CY154-85.13800.320.15750.00388.82020.23240.40170.00562429.341.02319.624.12176.725.810.4%
CY154-28.15670.370.14480.00338.19060.25230.40310.00722284.934.12252.327.92183.333.24.4%
CY154-46.14130.610.14970.00338.59100.19290.41480.00482342.937.52295.620.52236.821.84.5%
CY154-31.1910.600.15060.00388.86830.25180.42480.00742353.743.52324.526.02282.533.43.0%
CY154-15.12660.480.17530.003410.50720.25290.43270.00812608.333.52480.622.42317.836.611.1%
CY154-49.11610.820.15650.00409.44340.23240.43580.00522418.242.42382.122.72331.723.43.6%
CY154-20.11101.220.16050.003910.50320.25470.47210.00562460.840.72480.222.52492.724.5-1.3%
CY154-05.11570.540.17380.003512.38510.25770.51450.00552594.133.52634.019.62675.823.7-3.1%
CY154-32.11720.370.25730.005121.40300.51260.59680.00833231.531.53157.023.33017.033.76.6%


The zircons from the metapsammite sample CY011 mostly have Paleoproterozoic to Archean ages, except for one grain of Mesozoic age (ca. 215 Ma). Therefore, it is impossible to estimate the meaningful maximum depositional age of the protolith.

The tuffaceous sedimentary rock samples, CY146 and CY154, have similar age distribution, with major peaks of Middle Jurassic (172 and 170 Ma) and Paleoproterozoic ages. The age spectrum of CY146 mainly consists of Paleo-proterozoic (71%) and Middle Jurassic zircons (12%), whereas CY154 has a higher proportion of the Middle Jurassic grains (32%). The youngest 206Pb/238U single grain age from the samples is ca. 161 Ma. Our results indicate that the tuffaceous sedimentary rocks were deposited in Middle Jurassic or later.

4. Geological Structures

NE–SW trending reverse faults, NNE–SSW to NNW–SSE trending strike–slip or thrust faults, an NW–SE trending strike–slip fault, and related fold systems gently plunging toward the southwest are major geological structures in the study area (Fig. 2). Based on the structural positions, the fault structures are classified into intra-basin, basin-bounding, and basement fault systems. (1) The NE–SW trending faults and folds compose a basement fault system with a reverse sense of movement, including the Gooksa Fault that placed the Paleoproterozoic metamorphic basement rocks upon the age-unknown metapsammite. (2) The NNE–SSW to NNW–SSE trending faults occur as intra-basin, basin-bounding, and basement fault systems. The NNE–SSW and NNW–SSE faults in the basement rocks adjoin the NE–SW faults, thus defining branch lines in part and showing kinematic indicators, such as subsidiary fractures and slickenlines, which are indicative of a sinistral sense of movement. On the other hand, the basin-bounding or intra-basin NNE–SSW trending faults occur as low-angle thrusts accompanied by fault-related folds (e.g., Sindae anticline–syncline pair; Fig. 2); some of them are strongly tilted and accommodated sinistral strike–slip movements. (3) The NW–SE trending fault is the northeastern boundary of the Chungnam Basin. It spatially arrests the basin-bounding or intra-basin NNE-SSW trending faults, probably indicating the role of a transfer fault. To summarize, the geological structures in the study area accommodated a crustal shortening leading to the complex architecture of an inverted basin. Furthermore, Early Cretaceous quartz veins filling the fault systems imply that they are injected in association with the basin inversion.

5. Discussion and Conclusions

Our new geological, structural, and geochronological data on the Sindaeri area of the northeastern Chungnam Basin markedly reveal a successive Mesozoic crustal evolution, supporting the recent tectonic and crustal evolution model of the southwestern Korean Peninsula (e.g., S.-I. Park et al., 2018, 2019; J.-Y. Park et al., 2020; Park and Park, 2020; Lee et al., 2021). The Middle Jurassic zircon U–Pb ages of the rhyolitic tuff and tuffaceous sedimentary rocks likely reflect the intra-arc volcano-sedimentary process in a contemporary continental arc setting, which has been formerly reported from the Oseosan Volcanic Complex and, in turn, presented as evidence of a two-phase extension of the Chungnam Basin (Park et al., 2018). The complex basin inversion structures deforming the Middle Jurassic volcano-sedimentary sequence in the study area demonstrate a new orogenic cycle and related crustal shortening after the Middle Jurassic.

Notably, the inversion-related fault system in the study area is filled with gold-bearing quartz veins, indicating that the hydrothermal fluid migration was contemporaneous with the contractional deformation. Although it has been suggested that mesothermal quartz veins ubiquitously form by fault-valve behavior related to unfavorable high-angle reverse faulting and resultant crustal fluid redistribution in inverted extensional basins (Sibson et al., 1988; Sibson and Ghisetti, 2018; Blenkinsop et al., 2020; Kwak et al., 2022 and references therein), the characteristics and processes of fluid circulation related to Mesozoic orogenic events in the southwestern Korean Peninsula remain unsolved. Interestingly, the reported sericite and K-feldspar K-Ar isotopic ages from hydrothermally altered basements and basin-fills in the inverted Chungnam Basin and adjacent area (ca. 135–110 Ma) (So et al., 1988; Park et al., 2018) imply that the circulated crustal fluid is not related to orogenic magmatism, considering the Late Jurassic to Early Cretaceous magmatic quiescence in the southern Korean Peninsula (ca. 160–110 Ma) (Sagong et al., 2005; Kim et al., 2016).

In this context, what we need to obtain from further studies are (1) more detailed structural geometric and kinematic data from Mesozoic inverted basins in the southwestern Korean Peninsula to better understand the crustal deformation history and make the tectonic evolution model more sophisticated;(2) detailed geochronological data to clarify the temporal relationship between the genesis of mineral deposits and basin inversion; (3) more detailed microstructural data of the veins to improve understanding of vein growth mechanisms, fluid transport processes, and fluid–rock interactions. Further studies would provide essential insights into the relationship between the Mesozoic tectonics, basin inversion, and orogenic fluid circulation in the southwestern Korean Peninsula.

Acknowledgments

This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (No. 20212010200020). This research was also supported by the Basic Research Project grants (GP2020-003; Geological survey in the Korean Peninsula and publication of the geological maps) from the Korea Institute of Geoscience and Mineral Resources (KIGAM) funded by the Ministry of Science, Information, Communication and Technology (ICT), and Future Planning, Korea. We appreciate two anonymous reviewers for their constructive comments, which improved the manuscript.

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