• The Journal of the Petrological Society of Korea
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• v.17 no.2
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• pp.51-56
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• 2008

The geologic age of the Okcheon metamorphic belt, used to be a longstanding puzzle, has been settled down to Neoproterozoic to Paleozoic with discovery of fossils and isotopic age dating of metavolcanic rocks. As isotopic ages become accumulated, there appeared a controversy over the age of peak metamorphism in the Okcheon metamorphic belt, i.e., a single late Permian-early Triassic metamorphism (CHIME allanite age and U-Pb age of metamorphic zircon), or earlier independent presence of early Permian metamorphism (U-Pb age of allanite within garnet porphyroblast). If we compare the isotopic ages that can represent metamorphism, the data for the latter have much larger error than those of the former with some overlap considering the error limits. It means that, the former, supported by two independent ages, is considered a better representation for the age of metamorphism of the Okcheon metamorphic belt. Therefore, I propose the idea of early Permian metamorphism should better be reserved until conclusive evidence appears. The late Permian-early Triassic metamorphic age suggest that the effect of continental collision influenced much of the middle part of Korean Peninsula, namely, the Imjingang belt, the Gyeonggi massif and the Okcheon belt.

• Journal of the Korean earth science society
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• v.26 no.7
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• pp.624-629
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• 2005

Numerical data of the geological time scale in Earth Science I, II textbooks and those of University textbooks of Korea and other countries are briefly reviewed. Numerical data of the geologic time scale shown in Earth Science I, II textbooks are mostly out of date and many of them follow those in the University textbooks of Korea. The same situation is apparent for introductory Earth Science or Geology textbooks of other countries as old data exist in their text books as well. There are many new data in the International Stratigraphic Chart (ISC 2000) and International Geologic Time Scale (IGTS 2003) recently updated by International Commission on Stratigraphy (ICS) and A Geologic Time Scale (GTS 2004). Among the new data, some important things are Paleogene and Neogene Periods of Cenozoic Era, Mississippian and Pensilvanian Epochs of Carborniferous Period, Paleoproterozoic, Mesoproterozoic, and Neoproterozoic Eras of Proterozoic Eon, and Eoarchean, Paleoarchean, Mesoarchean, and Neoarchean Eras of Archean Eon. These new data should be used in the new Earth Science textbooks.

• The Journal of the Petrological Society of Korea
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• v.27 no.1
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• pp.67-72
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• 2018

The K-Ar ages of a sericite quartz schist in the lower Jangsan Formation along the Okdong fault zone reported by Yun (1983) have attracted attention again because of their potential to constrain the depositional timing of the Jangsan Formation. The oldest age of $562{\pm}2Ma$ among three reported K-Ar ages in the schist led to the claim that the depositional period of the lowermost Jangsan Formation in the Joseon Supergroup is late Neoproterozoic. Its depositional age is important for understanding the tectonic evolution of the Korean Peninsula including the formation and evolution histories of its sedimentary basins. Thus, the reliability and geological meaning of three K-Ar ages in the original paper (Yun, 1983) were revisited in the review. Quartz grains in the analyzed sample contain a considerable amount of excess Ar, and therefore it is inappropriate to use the ages as a basis for a depositional age constraint of the Jangsan Formation. The timing of mylonitization in the schist is recalculated as ~170 Ma.

• Economic and Environmental Geology
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• v.46 no.5
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• pp.391-409
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• 2013

The Hongseong area of the southwestern Gyeonggi massif is considered to be part of suture zone that is tectonically correlated with the Qinling-Dabie-Sulu belt of China in terms of the preservation of collisional evidences during Triassic in age. The Wolhyeonri complex, preserved at the center of the Hongseong area, consists mainly of Neoproterozoic orthogneisses and Middle Paleozoic intermediate- to high-grade metamorphic schists, orthogneisses and mafic metavolcanics. The area includes various Middle to Late Triassic intrusives (e.g. dyke or stock). They are mainly monzonite and aplite with small intrusions of monzodiorit, syenite and diorite in composition. The SHRIMP U-Pb zircon ages yield 237 Ma to 222 Ma. The geochemistry of the studied Triassic intrusives show similar subuction- or arc-type signatures having Ta-Nb troughs, depletion of P and Ti, and enrichment of LILEs (large ion lithophile elements). In addition, the Triassic plutons in the Hongseong area, including those from this study, mostly possess high-K calc-alkaline to shoshonitic tectonic affinity. These results could be tectonically correlated to the post-collisional magmatic event following the Triassic collision between the North and South China blocks in China. Therefore, the Triassic plutons in the Hongseong area offer an important insight into the Triassic geodynamic history of the NE Asian region.

• The Journal of the Petrological Society of Korea
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• v.21 no.2
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• pp.89-112
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• 2012

The Korean Peninsula consists of three Precambrian blocks: Nangrim, Gyeonggi and Yeongnam massifs. Here we revisited previous stratigraphic relationships, largely based on new geochronologic data, and investigated the crustal evolution history of the Precambrian massifs. The Precambrian strata have been usually divided into lower crystalline basements and upper supracrustal rocks. The former has been considered as Archean or Paleoproterozoic in age, whereas the latter as Paleoproterozoic or later. However, both are revealed as the Paleoproterozoic (2.3-1.8 Ga) strata as a whole, and Archean strata are very limited in the Korean Peninsula. These make the previous stratigraphic system wrong and require reconsideration. The oldest age of the basement rocks can be dated as old as Paleoarchean, suggested by the occurrence of ~3.6 Ga inherited zircon. However, most of crust-forming materials were extracted from mantle around ~2.7 Ga, and produced major portions of crust materials at ~2.5 Ga, which make each massif a discrete continental mass. After that, all the massifs belonged to continental margin orogen during the Paleoproterozoic time, and experienced repeated intracrustal differentiation. After the final cratonization occurring at ~1.9-1.8 Ga, they were stabilized as continental platforms. The Nangrim and Gyeonggi massif included local sedimentary deposition as well as igneous activity during Meso-to Neoproterozoic, but the Yeongnam massif remained stable before the development of Paleozoic basin.

• The Journal of the Petrological Society of Korea
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• v.21 no.1
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• pp.31-45
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• 2012

We investigated the various lithologies and zircon U-Pb ages of metasedimentary rocks from the Yeongheung-Seonjae-Daebu Islands, western Gyeonggi Massif, whose geologic and geochronologic features are poorly constrained in spite of their significance for tectonic interpretation. Major lithology consists of quartzites or meta-sandstones commonly alternating with semi-pelitic schists, together with lesser amounts of calcareous sandstones with matrix-supported quartzite clasts, calcareous schists, and pelitic schists. Pelitic schists uncommonly contain large porphyroblasts of garnet as well as quartz veins with large crystals of muscovite and andalusite or kyanite. SHRIMP U-Pb ages of detrital zircons from two analyzed metasandstones define four age populations: Neoarchean (~2.5 Ga), Paleoproterozoic (~2.0-1.5 Ga), Neoproterozoic (~1.1-0.7 Ga), and Early Paleozoic (~560-400 Ma). The youngest zircon ages are clustered at ~420 Ma. These results suggest that the deposition of meta-sandstones took place after the Silurian, possibly during the Devonian, and are analogous to those of the Taean Formation reported from the western part of the Gyeonggi Massif. Moreover, The age distribution patterns of detrital zircons and the Barrovian-type metamorphic facies of pelitic schists are similar to those reported from the Imjingang belt, suggesting that the Taean Formation likely corresponds to southwestward extension of the Imjingang Belt.

• Economic and Environmental Geology
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• v.49 no.2
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• pp.155-165
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• 2016

Quartz schist - quartzite is often intercalated in metasedimentary rocks of Ogcheon belt or aligned parallel to the boundary between Yeongnam massif and Ogcheon belt. However, stratigraphic sequence and or geologic age of the rocks has been still variable among authors as Precambrian or Paleozoic. In this study, we carried out SHRIMP U-Pb age data of detrital zircons from Yeongam and Yeongsanpo areas and compared ours with other zircon ages from other areas. The detrital zircons from the studied area show no age younger than 1.8 Ga but yielded clusters at Neoarchean (2.5 Ga) and Paleoproterozoic (1.8 Ga). On the other hand, the age range of zircon U-Pb dating of Paleozoic quartzites yielded from Archean to middle Paleozoic and clusters at Paleoproterozoic, Neoproterozoic and Paleozoic. The characteristics of the zircon age range and the dominant age peak might become a key to classify the Proterozoic to Paleozoic quartz schists-quartzites, which ages are still remained under controversy. Based on the statistical results of the zircon ages in this study, quartz schist - quartzite from Yeongam and Yeongsanpo is considered to be deposited during Proterozoic.

• Economic and Environmental Geology
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• v.49 no.4
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• pp.315-323
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• 2016

This study reports a gneiss dome in the Hongseong area, southwestern margin of the Gyeonggi massif. This gneiss dome, named here as 'Oseosan dome' because it is located around the Oseosan, the highest peak along the western coastal area, is composed mainly of the Neoproterozoic to Paleozoic ortho- and paragneiss, mafic metavolcanic rock, and metadolerite. Migmatization affected these rock units, in which leucocratic(granitic) materials derived from anatexis frequently occur as patch and vein parallel to or cutting through internal foliation. The Oseosan dome shows overall concentric geometry and outward-dipping internal foliation, but also partly complicatedly changeable or inward-dipping foliation. Taking available petrological and geochronological data into account, the Oseosan dome is interpreted to be exhumed quickly into the upper crustal level during the Late Triassic, accompanied in part with anatexis and granite intrusion. In addition, extensional shear zone intruded by the Late Triassic synkinematic granite and sedimentary basin have been reported around the Oseosan dome. These evidences possibly suggest that the Oseosan dome formed in closely associated with the Late Triassic extensional movement and diapiric flow. Alternatively, 1) thrust- or reverse fault-related doming or 2) interference between independent folds during structural inversion of the Late Traissic to Middle Jurassic sedimentary basin can be also considered as dome-forming process. However, considering the northern limb of the Oseosan dome, cutting by the Late Traissic granite, and the southern limb, cutting by contractional fault reactivated after the Middle Jurassic, it is likely that the domal structure formed during or prior to the Late Triassic.

• The Journal of the Petrological Society of Korea
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• v.19 no.1
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• pp.89-101
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• 2010

To constrain the depositional ages of the Gyeongsang sedimeantary formations, SHRIMP U-Pb ages were determined from detrital zircons in three samples: (1) a pebble-bearing sandstone from the lowermost Jinju Formation of the Sindong Group and (2) two conglomerates from the Silla Conglomerate of the Hayang Group. Their concordia ages are $112.4{\pm}1.3(2{\sigma})$ Ma and $110.4{\pm}2.0(2{\sigma})$ Ma respectively. Such ages represent the maximum deposition ages for the lowermost Jinju Formation and Silla Conglomerate, indicating the deposition of the Jinju Formation started from late Aptian and lasted to early Albian, then deposition of the rather thin Chilgok Formation and Silla Conglomerate was followed during the Albian. The age distribution of the analyzed detrital zircons indicates the presence of protoliths, or zircons derived from them, regarding a wide span of igneous activities from Mesozoic to Archean. Among such ages, there are Mesoproterozoic, Neoproterozoic and Paleozoic igneous activities, which have not been known or seldom reported from Korean peninsula. These ages further suggest the possible presence of rocks with such ages during the deposition periods or their derivation through a long river system developed into the continents at the time of deposition.

• The Journal of the Petrological Society of Korea
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• v.23 no.1
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• pp.17-30
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• 2014

In this study we carried out SHRIMP U-Pb age dating of detrital zircons from age-unknown meta-sedimentary formations distributed around the NNE-SSW trending Gwangju Shear Zone, a branch of Honam Shear Zone, in the southwestern region of the Korean Peninsula. The meta-sedimentary formations from the west (Yeonggwang) and east (Jangseong) areas of the Gwangju Shear Zone have different patterns of zircon age distributions. Zircons of quartzites from the Yeonggwang area yield clusters at Neoarchean (ca. 2,500 Ma), Paleoproterozoic (ca. 1,860 Ma), Neoproterozoic (ca. 960 Ma) and Paleozoic (ca. 380 Ma) ages, but those of the Jangseong area yield clusters at only Neoarchean (ca. 2,500Ma) and Paleoproterozoic (ca. 1,880 Ma) ages. The contrastive patterns in age indicate that the meta-sedimentary formations from the west and east areas correspond to the meta-sedimentary formations of the Okcheon Metamorphic Belt and the sedimentary formations overlying on the Yeongnam Massif, respectively. The results imply that the Gwangju Shear Zone is the tectonic boundary between the Okcheon Metamorphic Belt and the Yeongnam Massif.