pISSN 1225-7281 자원환경지질, 제53권, 제5호, 631-643, 2020 eISSN 2288-7962 Econ. Environ. Geol., 53(5), 631-643, 2020 http://dx.doi.org/10.9719/EEG.2020.53.5.631

Revised Geology of the Deokjeok and Soya Islands in the Central-western Korean Peninsula

Jeong-Yeong Park and Seung-Ik Park* Department of Geology, Kyungpook National University, Daegu 41566, Korea (Received: 21 August 2020 / Revised: 9 September 2020 / Accepted: 13 September 2020)

The central-western Korean Peninsula contains records of an Early Mesozoic collisional event related to the final amal- gamation of the East Asian continent. Here, we present a renewed geologic map of the Deokjeok and Soya islands in the central-western Korean Peninsula and its explanatory note. Our geologic map was based on a detailed investigation of the northeastern area of both islands, which is characterized by a complex fault and shear zone system that accommodated the crustal deformation related to the Mesozoic post-collisional orogenic collapse and the subsequent structural inversion. We suggest future directions of study aiming at addressing issues regarding the deformational responses of crust to the Mesozoic tectonic transition and orogenic cycles. Key words : geologic map, Deokjeok and Soya islands, central-western Korean Peninsula, mesozoic orogenic cycle, crustal deformation

1. Introduction various lithologic units, ranging in age from Paleo- proterozoic to Mesozoic, and suggested the presence The central-western Korean Peninsula has been of clear sedimentation, magmatism, metamorphism, recently proposed to be part of an orogenic belt and crustal deformation records related to post- preserving Precambrian to Phanerozoic multiple orogenic processes that followed the Early Mesozoic orogenic cycles (Oh et al., 2005, 2014; Kim et al., collision (Kim et al., 2014; Cho and Lee, 2016; 2006, 2008, 2013, 2017, 2018, 2019; Kwon et al., Park et al., 2020). Given the diverse aspects of post- 2009; Cho et al., 2017; Park et al., 2017, 2018, orogenic crustal modifications in these areas, the 2019; Lee et al., 2019). Lines of petrological, Deokjeok and Soya islands are considered excellent geochemical, and geochronological evidence (Oh natural laboratories. In fact, the full-cycled Mesozoic et al., 2005; Kim et al., 2006; Oh and Kusky, evolutionary history of the central-western Korean 2007; Kwon et al., 2009; Park et al., 2014) have Peninsula can be clarified by investigating their revealed that the area is tectonically correlated to territories. In particular, detailed geologic analyses the Qinling–Dabie–Sulu orogenic belt in China and can provide an improved understanding of the Meso- contains records of an Early Mesozoic collisional zoic orogenic evolution of the Korean Peninsula. event related to the closure of the Paleo-Tethys Here, we present a new geologic map of the Ocean and the final amalgamation of the East Deokjeok and Soya islands and an explanatory Asian continental margin. note revised from the Deokjeokdo sheet (Cho and The Deokjeok and Soya islands are located in the Lee, 2016). This geologic map reflects the result central-western Korean Peninsula (Fig. 1). Recent of our detailed mapping along the northeastern work on these islands has led to the definition of part of the islands, which is characterized by a

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*Corresponding author: [email protected]

631 632 Jeong-Yeong Park and Seung-Ik Park

Fig. 1. (a) Simplified tectonic map of the Korean Peninsula and adjacent areas (modified from Cluzel, 1992; Zheng et al., 2013). The gray box denotes the area shown in Fig. 1b. (b) Geologic map of the central-western Korean Peninsula (adapted from Kim et al., 2019). The gray rectangular box indicates the study area, which includes the Deokjeok and Soya islands. complex fault and shear zone system controlling 2.1. Paleoproterozoic metaplutonic rocks the distribution of the main lithologic units. From Paleoproterozoic metaplutonic rocks are distributed this map, we obtained new insights on the geology along the northwestern coast of the Deokjeok Island, of the Deokjeok and Soya islands, and especially and occur either as a small basement terrain or a on the Mesozoic tectonic transitions and orogenic fault-bounded sliver. The corresponding lithologic cycles in the central-western Korean Peninsula. On unit is mainly composed of metagranitic and meta- this base, we propose future directions of study to dioritic rocks. In the metagranitic rocks, subhedral address issues regarding the deformational responses to anhedral porphyroclasts of pinkish K- of crust to the orogenic evolution of this area. (ranging from 1 mm to 10 cm in size) are embedded in a groundmass composed mainly of , 2. Lithologic Units feldspar, and (Fig. 3a, b). Meanwhile, the metadioritic rocks are medium- to coarse- The lithologic units observed on the Deokjeok grained, have a bluish gray color (Fig. 3c), and are and Soya islands are shown in our new geologic mainly composed of amphibole and plagioclase, map (Fig. 2). A detailed description of the lithologic associated with minor quartz, chlorite, apatite, units is reported below. zircon, and opaque . Additionally, these Revised Geology of the Deokjeok and Soya Islands in the Central-western Korean Peninsula 633

Fig. 2. New geologic map and cross-sections of the Deokjeok and Soya islands. Abbreviations: N.F.―Neungdong Fault, B.T.―Buk-ri Thrust, K.F.―Keunmal Fault. rocks contain feldspar porphyroclasts with a long strikes NNE–NW and dips consistently north- axis of up to 7 cm (Fig. 3c, d). Notably, the deformed eastward at 50°–80°. The schist is frequently metadioritic rock occurring along the boundary cut by quartz veins with widths of several to tens with the Deokjeok Formation presents foliation, of centimeters, which are subperpendicular or which is associated with strongly elongated feldspar subparallel to the foliation (Fig. 4c). This lithologic porphyroclasts (Fig. 3e, f). The protolith age of this unit locally contains meta-conglomerate layers; the unit is Paleoproterozoic and was obtained through pebbles contained within them (with long axes up to zircon U–Pb isotopic analyses: most of the zircons 10 cm long) are aligned along the foliation (Fig. 4d). yielded 207Pb/206Pb apparent ages ranging from ca. Based on the youngest U–Pb age (ca. 980 Ma) 1870 to 1840 Ma (Park et al., unpublished data, obtained from the analysis of detrital zircon cores 2018). extracted from the mica schist, Cho and Lee (2016) have stated that its protolith should have 2.2. Neoproterozoic mica schist deposited during the Neoproterozoic. Moreover, Neoproterozoic mica schist is well exposed in based on the U–Pb isotopic data obtained from the the northern part of Deokjeok Island. They are analysis of the detrital zircons’ overgrowth rims, brown, medium- to coarse-grained, and composed the same authors proposed a Late Permian to Early mainly of muscovite, biotite, and quartz with minor Triassic (ca. 259–248 Ma) metamorphism. opaque minerals (Fig. 4a, b). This lithology displays a strong foliation, defined by the alignment of 2.3. Paleozoic mica schist elongated quartz aggregates and mica, that generally Paleozoic mica schist is locally distributed in the 634 Jeong-Yeong Park and Seung-Ik Park

Fig. 3. Photographs of the Paleoproterozoic metaplutonic rock. (a) Outcrop photograph of the metagranitic rock. (b) Photomicrograph (cross-polarized light) of the metagranitic rock. (c) Outcrop photograph of the metadioritic rock. (d) Feldspar porphyroclasts in the metadioritic rock. (e) Outcrop photograph of the extremely deformed metadioritic rock. (f) Photomicrograph (cross-polarized light) of the deformed metadioritic rock. Abbreviations: Am―Amphibole, Qtz―Quartz, Kfs―K-feldspar, Pl―Plagioclase. northernmost part of Deokjeok Island and is overlain and of the oldest , is ca. 435–379 Ma by the Early Jurassic Deokjeok Formation. This (Cho and Lee, 2016). lithology is bluish gray, medium-grained, and consists mainly of quartz, muscovite, and biotite. 2.4. Late Triassic biotite Moreover, it displays a strong foliation (Fig. 5), Late Triassic biotite granite is most widely which is defined by the alignment of muscovite, distributed on Deokjeok Island. It is typically gray biotite, and elongated quartz aggregates, generally to light gray, equigranular, and fine- to medium- striking NNW, and dipping northeastward. Its grained, but locally shows a porphyritic texture protolith age, which was defined based on the (Fig. 6a). This lithology is primarily composed of zircon U–Pb isotopic ages of the youngest detritus quartz, plagioclase, alkali feldspar, and biotite. Revised Geology of the Deokjeok and Soya Islands in the Central-western Korean Peninsula 635

Fig. 4. Photographs of the Neoproterozoic mica schist. (a) Outcrop photograph of the mica schist. (b) Photomicrograph (cross-polarized light) of the mica schist. (c) Outcrop photograph showing quartz veins subperpendicular to the foliation of the mica schist. (d) Outcrop photograph of the meta-conglomerate layer with elongated pebbles. Abbreviations: Qtz— Quartz, Ms—Muscovite.

foliation generally strikes NW, dips northeastward, and the stretching lineation plunges northeastward. Based on zircon U–Pb isotopic analysis, the emplacement age of the biotite granite was defined to be ca. 223 Ma (Cho and Lee, 2016).

2.5. Late Triassic quartzolite Late Triassic quartzolite is distributed in the northeastern part of Soya Island, and occurs in the form of thick fine-grained quartzose layers (Fig. 7a) trending NW (parallel to the mylonitic foliation in the nearby deformed ). This lithology is Fig. 5. Outcrop photograph of the Paleozoic mica schist. mainly composed of quartz with minor biotite and was mylonitized by ductile shearing. The mylonitic foliation generally strikes NW, dips northeastward, Sericite commonly occurs in altered ; and is marked by a stretching lineation plunging moreover, zircon, epidote, and opaque minerals northeastward. Slightly elongated quartz grains occur as accessory minerals. The biotite granite define a steady state (oblique) foliation in the along the northeastern coast of Deokjeok Island deformed quartzolite (Fig. 7b); additionally, the was strongly deformed in a ductile manner, and mylonitic fabrics are locally cut by thin massive hence converted to mylonite or protomylonite with quartz veins (Fig. 7b). penetrative fabrics (Fig. 6b, c). The mylonitic This lithologic unit corresponds to the Paleozoic 636 Jeong-Yeong Park and Seung-Ik Park

Fig. 7. Photographs of the Late Triassic quartzolite. (a) Outcrop photograph of the quartzolite. (b) Microphotograph (cross-polarized light) of the quartzolite. Abbreviation: Qtz—Quartz.

this lithologic unit, we redefined it as a Late Triassic quartz-rich intrusive body (‘a quartzolite’).

2.6. Late Triassic layered intrusive rock Late Triassic layered felsic intrusive rock is exposed in the easternmost part of Deokjeok Fig. 6. Photographs of the Late Triassic biotite granite. (a) Island and in the northeastern part of Soya Island. Outcrop photograph of the biotite granite. (b) Outcrop This lithology is composed of alternations of thin photograph of the mylonitized biotite granite. (c) Micro- leucocratic layers (thickness of up to 10 cm) and photograph (cross-polarized light) of the mylonitized biotite granite. Abbreviations: Qtz—Quartz, Kfs—K-feldspar, thick gray layers (thickness between several centi- Bt—Biotite. meters to 1 m) (Fig. 8a). Its layers strike NW and generally dip northeastward. The leucocratic layer quartz schist previously described by Cho and Lee is fine-grained and mainly composed of quartz, (2016). However, most of the apparent 206Pb/238U alkali feldspar, plagioclase, and biotite (Fig. 8b), dating analyses indicate a Late Triassic age (ca. moreover, some altered feldspars transformed into 220 Ma; Park et al., unpublished data, 2019). sericite. The gray layers are extremely fine-grained Notably, the quartzolite is not spatially associated and consist mainly of quartz, alkali feldspar, and with metasedimentary sequences, but rather with the plagioclase with minor microcline, epidote, chlorite, Late Triassic intrusive rocks described previously and sericite (Fig. 8c). Down-dip verging asymme- and below (Fig. 2). Based on the composition, trical folds ubiquitously occur in the layered felsic lithologic assemblage, and U–Pb isotopic data of intrusive rock (Fig. 8a). Finally, most of the igneous Revised Geology of the Deokjeok and Soya Islands in the Central-western Korean Peninsula 637

Fig. 8. Photographs of the Late Triassic layered felsic intrusive Fig. 9. Photographs of the Late Triassic porphyritic granite. rock. (a) Outcrop photograph of the layered felsic intrusive (a) Outcrop photograph of the porphyritic granite. (b) Outcrop rock showing a down-dip verging asymmetric fold. (b) photograph of the mylonitized porphyritic granite. (c) Microphotograph (cross-polarized light) of the leucocratic Microphotograph (cross-polarized light) of the mylonitized layer. (c) Microphotograph (cross-polarized light) of the gray porphyritic granite. Abbreviations: Qtz—Quartz, Kfs—K- layer. Abbreviations: Qtz—Quartz, Kfs—K-feldspar. feldspar, Bt—Biotite. zircons from the layered felsic intrusive rock yielded shows a gradual transition in the abundance of apparent 206Pb/238U ages ranging between ca. 220– alkali feldspar phenocryst: this is a unique criterion 215 Ma (Park et al., unpublished data, 2018). to distinguish lithologic units. The major axis of the alkali feldspar phenocrysts is about 4–5 cm 2.7. Late Triassic porphyritic granite long (Fig. 9a) and their preferred orientation locally Late Triassic porphyritic granite is distributed defines a magmatic foliation that generally strikes along the eastern coast of Deokjeok Island and on NW and dips northeastward. Along the eastern Soya Island. This lithology has a mineral compo- coast of Deokjeok Island and the northeastern sition similar to that of the biotite granite and coast of Soya Island, the porphyritic granite was 638 Jeong-Yeong Park and Seung-Ik Park

Fig. 10. Outcrop photograph showing field evidence of Fig. 11. Photographs of the Late Triassic syenogranite. (a) diorite-granite magma mingling. (a) Contact between the Outcrop photograph of the mylonitized syenogranite. (b) Late Triassic diorite and the porphyritic granite. (b) Diorite Microphotograph (cross-polarized light) of the mylonitized inclusions in the Late Triassic porphyritic granite. syenogranite. Abbreviations: Qtz—Quartz, Kfs—K-feldspar, Bt—Biotite. deformed in a ductile manner and converted into easternmost part of Soya Island and is characterized mylonite or protomylonite (Fig. 9b, c). The mylonitic by an overall pinkish color due to its significant foliation strikes NW and dips northeastward; content of alkali feldspar (Fig. 11a). This lithology moreover, it is marked by a stretching lineation was strongly deformed in a ductile manner and generally plunging northeastward. The emplacement mylonitized. The alkali feldspar porphyroclasts age of the porphyritic granite, defined by zircon contained within it have a maximum axis of about U–Pb isotopic analyses, is ca. 218 Ma (Cho and 3 cm and are embedded in a gray matrix. This Lee, 2016; Park et al., 2020). matrix mainly consists of alkali feldspar, plagio- clase, quartz, and biotite with minor zircon, 2.8. Late Triassic diorite epidote, and opaque minerals (Fig. 11b). The Late Triassic diorite is locally distributed in mylonitic foliation generally strikes NW and dips small stocks that invaded the porphyritic granite northeastward, while a stretching lineation plunges on Soya Island (Fig. 10a). This lithology is dark northeastward. Most of the igneous zircons from gray, fine- to medium-grained, and mainly consists the syenogranite yielded apparent 206Pb/238U ages of amphibole, feldspar, and biotite; moreover, diorite of ca. 220–210 Ma (Park et al., unpublished data, occurs in the form of inclusions in the porphyritic 2018). granite along the northeastern coast of Soya Island, suggesting a magma mingling process (Fig. 10b). 2.10. Late Triassic Jin-ri Formation The Jin-ri Formation is represented by Late 2.9. Late Triassic syenogranite Triassic volcano-sedimentary strata distributed Late Triassic syenogranite is distributed in the along the eastern coast of Deokjeok Island. This Revised Geology of the Deokjeok and Soya Islands in the Central-western Korean Peninsula 639 formation is composed of alternating layers of The volcanic layers of the Jin-ri Formation conglomerate, sandstone, and slate (Fig. 12a–c), yielded Late Triassic zircon U–Pb ages (ca. 221– all slightly metamorphosed and deformed. Pebble- 217 Ma), which likely indicate the timing of syn- bearing phyllite and volcanic rocks (i.e., felsic tuff depositional volcanism (Park et al., 2020). Park et and quartz porphyry) are conformably interlayered al. (2020) grouped the Jin-ri Formation into the in the sedimentary sequences (Park et al., 2020). Deokjeok Formation. However, based on the The sandstone is light to dark gray, medium- to differences in lithology, deposition age, metamorphic very coarse-grained, and locally contains subangular grade, and distribution, we define it here as a new quartz and feldspar fragments (Fig. 12b). In general, lithostratigraphic unit. the bedding of the Jin-ri Formation strikes NW and dips northeastward. Notably, the slaty and 2.11. Early Jurassic Deokjeok Formation phyllitic cleavages are subparallel to the bedding. The Deokjeok Formation, which was first named

Fig. 12. Outcrop photographs of the Late Triassic Jin-ri Fig. 13. Outcrop photographs of the Early Jurassic Formation. (a) Sandstones. (b) Pebbly sandstones with Deokjeok Formation. (a) Conglomerates. (b) Medium to feldspar fragments. (c) Gray slate. coarse sandstones. (c) Dark gray mudstones. 640 Jeong-Yeong Park and Seung-Ik Park by Cho and Lee (2016), is distributed in the Formation. Finally, the Keunmal Fault placed the northern part of Deokjeok Island and composed of Late Triassic granite over the Late Triassic Jin-ri alternating layers of conglomerate, sandstone, and Formation and defines the southwestern boundary mudstone (Fig. 13a–c). The conglomerate is composed of the SSZ. of subrounded to subangular , granite, gneiss, and volcanic clasts with sizes between 2– 4. Discussion and Conclusions 200 mm and dispersed in a light gray to brownish gray sandstone matrix (Fig. 13a). The sandstone is The central-western Korean Peninsula contains light to middle or brownish gray and fine- to records of a complex crustal deformation associated coarse-grained (Fig. 13b), while the mudstone is with Mesozoic plate marginal processes (Oh et al., dark gray (Fig. 13c). 2005; Kim et al., 2006; Kwon et al., 2009; Park et Based on the youngest zircon U–Pb age (ca. al., 2014, 2018, 2019, 2020; de Jong et al., 2015; 188 Ma), obtained from a volcanic pebble in the Cho et al., 2017). The overthickened crust of the conglomerate, Cho and Lee (2016) suggested that peninsula caused by an Early Mesozoic continental the Deokjeok Formation was deposited during the collision has been affected by high-K calc-alkaline Early Jurassic or later. and shoshonitic magmatism, metamorphism, and crustal stretching related to Late Triassic post- 3. Geologic Structures collisional processes (Kwon et al., 2009; Williams et al., 2009; Kim et al., 2011; de Jong et al., 2015; The lithologic units encountered on the Deokjeok Park et al., 2018, 2020). As the tectonic regime and Soya islands and described above are strongly changed to subduction, the central-western Korean controlled by NW–trending macro-scale ductile shear Peninsula started to be influenced by arc magmatism zones and a contractional fault system (Fig. 2). and local intra-arc subsidence during the Early to Along the eastern coasts of the Deokjeok and Soya Middle Jurassic (Park et al., 2009; Kee et al., 2010; islands, two NW-trending and NE-dipping ductile Kim et al., 2015; Park et al., 2018); moreover, a shear zones (i.e., Deokjeok Shear Zone (DSZ) and shortening and positive structural inversion of the Soya Shear Zone (SSZ)) are developed in the Late basement probably occurred due to the low-angle Triassic plutonic rocks (Fig. 2; Park et al., 2020). or flat subduction of the Paleo-Pacific Plate during Park et al. (2020) reported that the DSZ and the the Late Jurassic to Early Cretaceous (Park et al., SSZ have different structural positions and kine- 2018, 2019). matics. The DSZ structurally underlies the Late Within the Mesozoic tectonic framework of the Triassic Jin-ri Formation, and shows a top-down- central-western Korean Peninsula remarked above, to-the-northeast shearing. On the other hand, the the Deokjeok and Soya islands experienced multiple SSZ overlies the Late Triassic Jin-ri Formation, and Mesozoic crustal deformation events related to a contains evidences of a top-up-to-the-southwest tectonic transition (from post-collision to subduc- shearing following a top-down-to-the-northeast sense tion). The DSZ is an extensional high-strain zone of movement (Figs. 7 and 8 from Park et al., 2020). controlling the distribution of the Late Triassic Jin-ri Notably, the DSZ spatially separates the Late Formation. Since the Jin-ri Formation is juxtaposed Triassic to Early Jurassic sedimentary rocks from with the nearly contemporaneous mylonitized the Jin-ri Formation and the Deokjeok Formation. granite, the DSZ probably behaved as an extensional The NW- to N-trending contractional fault system detachment during the post-collisional orogenic identified on the Deokjeok and Soya islands includes collapse, as suggested by Park et al. (2020). The the Neungdong Fault, the Buk-ri Thrust, and the occurrence of the Deokjeok Formation in the Keunmal Fault (Fig. 2). The Neungdong Fault is a footwall of the DSZ indicates that the mechanical contractional fault that carried an isolated, lens- subsidence continued until the Jurassic. shaped and fault-bounded Paleoproterozoic basement The contractional fault system and the SSZ in sliver upon the Early Jurassic Deokjeok Formation. the Deokjeok and Soya islands suggest that a The Buk-ri Thrust, instead, placed the Neoproterozoic horizontal shortening followed the crustal extension mica schist over the Early Jurassic Deokjeok and that the area was structurally inverted. The Revised Geology of the Deokjeok and Soya Islands in the Central-western Korean Peninsula 641 isolated, fault-bounded basement sliver carried by 2015; Spanos et al., 2015; Mookerjee et al., 2016; the Neungdong Fault was geometrically and Behyari and Shahbazi, 2019). kinematically similar to a basement block formed A comprehensive study on the Deokjeok and by a shortcut faulting of a basement ramp and Soya islands and the adjacent areas will lead to an diagnostically recognized in diverse types of improved understanding of the Mesozoic structural inverted extensional basin (Hayward and Graham, and tectonic evolution of the central-western Korean 1989; Coward, 1994). The Jurassic to Early Peninsula as part of an orogenic belt, and of the Cretaceous subduction tectonics in the Korean diachronous aspect of the tectonic cycles in the Peninsula (Sagong et al., 2005; Kim et al., 2016) Mesozoic East Asian continental margin (Kim, were likely the cause of the basement-involved 2019; Jang and Cheong, 2019). crustal shortening and structural inversion noted on the Deokjeok and Soya islands and interpreted Acknowledgments in an adjacent area by Park et al. (2018, 2019), although additional geochronological data are This work was supported by the Basic Research required to confirm this idea. Program of the National Research Foundation of Further studies on the geology of the Deokjeok Korea (Grant no. 2018R1C1B6003851), which and Soya islands and adjacent areas will help to was funded by the Ministry of Science and ICT refine the correspondent structural and tectonic and granted to S.-I. Park. We thank Dr. Seung-Bae evolutionary models. 1) Detailed information of the Lee for his assistance in defining the geology of P-T-t path of the Neoarchean tonalitic migmatite the Deokjeok and Soya islands during the early on Daeijak Island (on the footwall side of the DSZ) stages of this study. Finally, we appreciate two is required to support the extensional detachment anonymous reviewers for their constructive com- model. Whether Late Triassic isothermal decom- ments, which improved the manuscript. pression and anatexis are recorded in the migmatite is important to test the detachment-controlled References orogenic collapse model (Teyssier and Whitney, 2002; Whitney et al., 2004). The Late Triassic U– Behyari, M. and Shahbazi, M. (2019) Strain and vorticity Th–Pb ages obtained from the allanite in the analysis in the Zagros suture zone (W Iran): Impli- cations for Neo-Tethys post-collision events. J. Struct. migmatite (Kim et al., 2009) raise the possibility Geol., v.126, p.198-209. of Late Triassic anatexis. 2) Deformation (i.e., Cho, D.-L. and Lee, S.-B. (2016) Geological report of mylonitization and faulting) ages are required to the Gureopdo·Deokjeokdo·Baegado·Seongapdo sheets clarify the relationship between the Late Jurassic (1:50,000). Korea Institute of Geoscience and Mineral Resources, 54p (in Korean with English abstract). to Early Cretaceous subduction tectonics and the Cho, M., Lee, Y., Kim, T., Cheong, W., Kim, Y. and Lee, structural inversion in the Deokjeok and Soya S.R. (2017) Tectonic evolution of Precambrian base- islands. The 40Ar/39Ar ages obtained from the ment massifs and an adjoining fold-and-thrust belt mica in the mylonite and K–Ar ages obtained from (Gyeonggi Marginal Belt), Korea: An overview. Geosci. J., v.21, p.845-865. fine-grained white mica in the cataclastic fault Cluzel, D. (1992) Formation and tectonic evolution of early rock (Oriolo et al., 2018 and references therein) Mesozoic intramontane basins in the Ogcheon belt would be useful to constrain the timing of crustal (South Korea): a reappraisal of the Jurassic “Daebo orogeny”. J. Southeast Asian Earth Sci., v.7, p.223-235. shortening and structural inversion following crustal Coward, M.P. (1994) Inversion tectonics. In Hancock, P.L. extension. 3) Strain and vorticity data are needed (ed.) Continental Deformation. Pergamon Press, p.280- to fully understand the kinematic evolution of 304. extensional and contractional structures in the de Jong, K., Han, S. and Ruffet, G. (2015) Fast cooling fol- lowing a Late Triassic metamorphic and magmatic Deokjeok and Soya islands. Detailed information pulse: implications for the tectonic evolution of the from the kinematic parameters on the material Korean collision belt. Tectonophysics, v.662, p.271-290. movement would be provide clues to reconstruct Hayward, A.B. and Graham, R.G. (1989) Some geometrical the spatio-temporal evolution of the tectonic characteristics of inversion. In Cooper, M.A. and Wil- liams, G.D.(eds.), Inversion Tectonics. Geological Soci- regime (e.g., Xypolias et al., 2010; Ring et al., ety of London, Special Publication, v.44, p.17-39. 642 Jeong-Yeong Park and Seung-Ik Park

Jang. Y. and Cheong, H.J. (2019) Sturctural Geometry of Kim, Y., Cheong, C.-S., Lee, Y. and Williams, I.S. (2009) the Pyeongchang-Jeongseon Area of the Northwestern SHRIMP allanite U-Th-Pb dating of bimodal Triassic Taebaeksan Zone, Okcheon Belt. Econ. Env. Geol., metamorphism of Neoarchean tonalitic gneisses, Daei- v.52, p.541-554 (in Korean with English abstract). jak Island, central Korea. Geosci. J., v.13, p.305-315. Kee, W.-S., Kim, S.W., Jeong, Y.-J. and Kwon, S. (2010) Kim, Y., Aum, H.W., Choeng, W., Kim, T. and Yi, K. Characteristics of Jurassic continental arc magmatism in (2014) An occurrence of the post-orogenic Triassic South Korea: tectonic implications. J. Geol., v.118, strata on Deokjeok Island, western Gyeonggi massif, p.305-323. Korea. Geosci. J., v.18, p.137-147. Kim, H.S. (2019) Reassessment of the Pyeongan Super- Kwon, S., Sajeev, K., Mitra, G., Park, Y., Kim, S.W. and group: Metamorphism and Deformation of the Songrim Ryu, I.-C. (2009) Evidence for Permo-Triassic collision Orogeny. Econ. Env. Geol., v.52, p.367-379 (in Korean in Far East Asia: the Korean collisional orogen. Earth with English abstract). Planet. Sci. Lett., v.279, p.340-349. Kim, S.W., Oh, C.W., Williams, I.S., Rubatto, D., Ryu, I.- Lee, H., Park, S.-I., Choi, T. and Sim, M.S. (2019) Post-col- C., Rajesh, V.J., Kim, C.-B., Guo, J. and Zhai, M. lisional denudation of an orogenic belt traced from geo- (2006) Phanerozoic high-pressure eclogite and inter- chronological and bulk-rock geochemical records of the mediate pressure granulite facies metamorphism in the western Korean Peninsula. Int. Geol. Rev., p.1-22. Gyeonggi massif, South Korea: implications for the doi:10.1080/00206814.2019.1706649. eastward extension of the Dabie-Sulu continental col- Mookerjee, M., Canada, A. and Fortescue, F.Q. (2016) lision zone. Lithos, v.92, p.357-377. Quantifying thinning and extrusion associated with an Kim, S.W., Williams, I.S., Kwon, S. and Oh, C.W. (2008) oblique subduction zone: An example from the Rosy SHRIMP zircon geochronology and geochemical char- Finch Shear Zone. Tectonophysics, v.693, p.290-303. acteristics of metaplutonic rocks from the south-western Oh, C.W. and Kusky, T. (2007) The Late Permian to Tri- Gyeonggi block, Korea: implications for Paleoprotero- assic Hongseong-Odesan Collision Belt in South Korea, zoic to Mesozoic tectonic links between the Korean and its tectonic correlation with China and Japan. Int. Peninsula and eastern China. Precambrian Res., v.162, Geol. Rev., v.49, p.636-657. p.475-497. Oh, C.W., Kim, S.W., Choi, S.G., Zhai, M., Guo, J. and Kim, S.W., Kwon, S., Koh, H.J., Yi, K., Jeong, Y. and San- Sajeev, K. (2005) First finding of eclogite facies met- tosh, M. (2011) Geotectonic framework of Permo-Tri- amorphic event in South Korea and its correlation with assic magmatism within the Korean Peninsula. the Dabie-Sulu collision belt in China. J. Geol., v.113, Gondwana Res., v.20, p.865-889. p.226-232. Kim, S.W., Kee, W.-S., Lee, S.R., Santosh, M. and Kwon, Oh, C.W., Imayama, T., Yi, S.-B., Kim, T., Ryu, I.-C., Jeon, S. (2013) Neoproterozoic plutonic rocks from the west- J. and Yi, K. (2014) Middle Paleozoic metamorphism in ern Gyeonggi massif, South Korea: Implications for the the Hongseong area, South Korea, and tectonic sig- amalgamation and break-up of the Rodinia supercon- nificance for Paleozoic orogeny in northeast Asia. J. tinent. Precambrian Res., v.277, p.349-367. Asian Earth Sci., v.95, p.203-216. Kim, S.W., Kwon, S., Ko, K., Yi, K., Cho, D.-L., Kee, W.- Oriolo, S., Wemmer, K., Oyhantçabal, P., Fossen, H., S. and Kim, B.C. (2015) Geochronological and geo- Schulz, B. and Siegesmund, S. (2018) Geochronology chemical implications of Early to Middle Jurassic con- of shear zones - A review. Earth-Sci. Rev., v.185, p.665- tinental adakitic arc magmatism in the Korean Peninsula. 683. Lithos, v.227, p.225-240. Park, J.-Y., Park, S.-I. and Choi, T. (2020) Microstructural Kim, S.W., Kwon, S., Park, S.-I., Lee, C., Cho, D.-L., Lee, and geochronological analyses of Mesozoic ductile H.-J., Ko, K. and Kim, S.J. (2016) SHRIMP U-Pb dat- shear zones in the Western Gyeonggi massif, Korea: ing and geochemistry of the Cretaceous plutonic rocks Implications for an orogenic cycle in the East Asian in the Korean Peninsula: A new tectonic model of the continental margin. Minerals, 10, 362. https://doi.org/ Cretaceous Korean Peninsula. Lithos, v.262, p.88-106. 10.3390/min10040362. Kim, S.W., Kwon, S., Park, S.-I., Yi, K., Santosh, M. and Park, S.-I., Kwon, S., Kim, S.W., Yi, K. and Santosh, M. Kim, H.S. (2017) Early to Middle Paleozoic tec- (2014) Continental origin of the Bibong eclogite, south- tonometamorphic evolution of the Hongseong area, cen- western Gyeonggi massif, South Korea. J. Asian Earth tral western Korean Peninsula: tectonic implications. Sci., v.95, p.192-202. Gondwana Res., v.47, p.308-322. Park, S.-I., Kim, S.W., Kwon, S., Santosh, M., Ko, K. and Kim, S.W., Cho, D.-L., Lee, S.-B., Kwon, S., Park, S.-I., Kee, W.-S. (2017) Nature of Late Mesoproterozoic to Santosh, M. and Kee, W.-S. (2018) Mesoproterozoic Early Neoproterozoic magmatism in the western Gyeo- magmatic suites from the central-western Korean Pen- nggi massif, Korean Peninsula and its tectonic signif- insula: Imprints of Columbia disruption in East Asia. icance. Gondwana Res., v.47, p.291-307. Precambrian Res., v.306, p.155-173. Park, S.-I., Kwon, S., Kim, S.W., Hong, P.S. and Santosh, Kim, S.W., Kwon, S., Santosh, M., Cho, D.-L., Kee, W.-S., M. (2018) A Mesozoic orogenic cycle from post-col- Lee, S.-B. and Jeong, Y.-J. (2019) Detrital zircon U-Pb lision to subduction in the southwestern Korean Pen- and Hf isotope characteristics of the Early Neopro- insula: new structural, geochemical, and chronological terozoic successions in the central-western Korean Pen- evidence. J. Asian Earth Sci., v.157, p.166-186. insula: Implication for the Precambrian tectonic history Park, S.-I., Noh, J., Cheong, H.J., Kwon, S., Song, Y., Kim, of East Asia. Precambrian Res., v.322, p.24-41. S.W. and Santosh, M. (2019) Inversion of two-phase Revised Geology of the Deokjeok and Soya Islands in the Central-western Korean Peninsula 643

extensional basin systems during subduction of the orogens. Geology, v.30, p.1139-1142. Paleo-Pacific Plate in the SW Korean Peninsula: Impli- Whitney, D.L., Teyssier, C. and Vanderhaeghe, O. (2004) cation for the Mesozoic “Laramide-style” orogeny Gneiss domes and crustal flow. In Whitney, D.L., Teys- along East Asian continental margin. Geosci. Front., sier, C. and Siddoway, C.S.(eds.), Gneiss domes in v.10, p.909-925. orogeny. Geological Society of America Special Paper, Park, Y.S., Kim, S.W., Kee, W.-S., Jeong, Y.-J., Yi, K. and v.380, p.15-33. Ki, J. (2009) Middle Jurassic tectono-magmatic evo- Williams, I.S., Cho, D.L. and Kim, S.W. (2009) Geo- lution in the southwestern margin of the Gyeonggi Mas- chronology, and geochemical and Nd-Sr isotopic char- sif, South Korea. Geosci. J., v.13, p.217-231. acteristics, of Triassic plutonic rocks in the Gyeonggi Ring, U., Bernet, M. and Tulloch, A. (2015) Kinematic, Massif, South Korea: constraints on Triassic post-col- finite strain and vorticity analysis of the Sisters Shear lisional magmatism. Lithos, v.107, p.239-256. Zone, Stewart Island, New Zealand. J. Struct. Geol., Xypolias, P., Spanos, D., Chatzaras, V., Kokkalas, S. and v.73, p.114-129. Koukouvelas, I. (2010) Vorticity of flow in ductile thrust Sagong, H., Kwon, S.-T. and Ree, J.-H. (2005) Mesozoic zones: examples from the Attico-Cycladic Massif (Inter- episodic magmatism in South Korea and its tectonic nal Hellenides, Greece). In Law, R.D., Butler, R.W.H., implication. Tectonics, 24. http://dx.doi.org/10.1029/ Holdsworth, R.E., Krabbendam, M., Strachan, R.A. 2004TC001720. (eds.), Continental Tectonics and Mountain Building: Spanos, D., Xypolias, P. and Koukouvelas, I. (2015) Vor- The Legacy of Peach and Horne. Geological Society of ticity analysis in calcite tectonites: An example from the London, Special Publication, v.335, p.687-714. Attico-Cycladic massif (Attica, Greece). J. Struct. Geol., Zheng, Y.-F., Xiao, W.-J. and Zhao, G. (2013) Introduction v.80, p.120-132. to tectonics of China. Gondwana Res., v.23, p.1189- Teyssier, C. and Whitney, D.L. (2002) Gneiss domes and 1206.