• The Journal of the Petrological Society of Korea
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• v.14 no.2 s.40
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• pp.83-92
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• 2005

It has recently been proposed that granites can be divided into hot and cold ones by absence and presence of inherited zircon, respectively, which is closely related to zircon saturation temperature. The Phanerozoic granites in South Korea are divided into high- and low-Zr groups in a $SiO_2-Zr$ diagram, which appears to be related to their intrusive age. Most Triassic-Jurassic granites belong to low-Zr group, whereas most Cretaceous-Early Tertiary granites belong to the high-Zr group with the exception of geographically distinct Masan and Jinhae granites that belong low-Zr group. Calculated zircon saturation temperatures using major elements and Zr contents indicate that the Cretaceous-Early Tertiary granites $(608-834^{\circ}C,\;average\; 782\pm31^{\circ}C)$ except for the Masan and Jinhae granites $(average\;759\pm16^{\circ}C)$ show higher temperature than the Triassic-Jurassic granites $(642-824^{\circ}C,\;average\;756\pm31^{\circ}C)$. U-Pb zircon isotope data of the Triassic-Jurassic granites reported so far define discordia in a concordia diagram, which indicates presence of inherited zircon and agrees with their low zircon saturation temperatures. So the Triassic-Jurassic granites appear to belong to cold granite. On the other hand, presence or absence of inherited zircon has not been known for the Cretaceous-Early Tertiary granites with relatively high zircon saturation temperature, so that their classification into hot or cold granite awaits further study. Nevertheless, the Creatceous-Early Tertiary granites may have formed at higher temperature than the Triassic-Jurassic granites, since zircon saturation temperature reflects formation temperature of magma to a certain degree.

• The Journal of the Petrological Society of Korea
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• v.14 no.4 s.42
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• pp.226-236
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• 2005

Using the concept of granite suite/supersuite we hierarchically divided the Triassic granites in South Korea which have spatio-temporally close relationships each other. Among the Triassic granites in the Okcheon belt (western Yeongnam massif), the Baegrok granite and the Jeomchon granite can be grouped into one suite, the Baegrok suite, whereas the Cheongsan granite into the Cheongsan suite. These two suites can be grouped again into a larger supersuite, the Baegrok supersuite, on the basis of the similarity in the source rocks and the contrasts in the petrographic and geochemical characteristics. Three Triassic granites in the Gyeongsang basin - the Yeongdeok granite, the Yeonghae granite, and the Cheongsong granite - can be grouped into the Yeongdeok suite, Yeonghae suite and Cheongsong suite, respectively. These three suites can be grouped again into a larger supersuite, the Yeongdeok supersuite, on the basis of the similarity in the source rocks and the contrasts in the petrographic and geochemical characteristics. Nd-Sr isotopic signatures for the Baegrok supersuite are quite distinct from those for the Yeongdeok supersuite, indicating that the source materials of each granitic magma were not identical. The source rocks for the Baegrok supersuite are thought to be a mixture of two crustal components of the Yeongnam massif, whereas those for the Yeongdeok supersuite to be a mixture of the depleted mantle with the crustal components of the Yeongnam massif. The fact that the two contemporaneous granite supersuites were derived from the different sources can be explained by the difference of the tectonic environments where the granitic magmas were produced.

• Economic and Environmental Geology
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• v.27 no.3
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• pp.247-261
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• 1994

Honam Shear Zone is a mylonite zone approximately parallel to the NE-SW trend located southern part of Korea peninsula. Geologic ages and petrogenesis of foliated granites in this zone are as follows: Igneous rocks of this zone are composed of granite gneiss, Paleozoic granites, Songrim granites, Jurassic granites and Cretaceous granites. Foliated granites show deformed phase of Paleozoic and Songrim granites during Daebo Orogeny. And isotopic ages obtained from foliated granites are early Permian to late Triassic period (276~200 Ma). Most of foliated granite masses are igneous complex consisting of a series of differential product of cogenetic magma. The individual rock mass of foliated granites plotted on Harker diagram shows mostly similar trend of calc-alkali series. REE diagram indicates that LREE amount of foliated granites are more enriched than HREE and negative Eu anomalies of them are weaker than those of the other granites. From these data, we suggest the rocks are generated from continental margin under syntectonic environment. Original magma type of foliated granites correspond to I-type, syn-collision type and Hercyano type. In compressive stress field between Ogcheon folded belt and Youngnam massif, foliated granites had formed due to mylonitic deformation. Those facts indicate that magma of foliated granites would had been generated by melting in lower crust or contamination in upper mantle.

• The Journal of the Petrological Society of Korea
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• v.2 no.2
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• pp.104-121
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• 1993

Fission track (FT) thermochronological analyses on Mesozoic granites provide new information about cooling and uplift histories in Southeast Korea. Twenty-nine new FT sphene, zircon and apatite ages and seven track length measurements are presented for eleven granite samples. Measured mineral ages against assumed closure temperatures yield cooling rates for each sample. Relatively rapid (7-$15^{\circ}C$/Ma) and simple cooling patterns from the middle Cretaceouss (ca. 90-100 Ma) granites are caused mainly by a high thermal contrast between the intruding magma and country rocks at shallow crustal levels (ca. 1-2.5 km-depths). On the contrary, a slow overall cooling (1-$4^{\circ}C$/Ma) of the Triassic to Jurassic granites (ca. 250-200 Ma), emplaced at deep depths (>>9 km), may mainly depend upon very slow denudation of the overlying crust. The uplift history of the Triassic Yeongdeog Pluton in the Yeongyang Subbasin, west of the Yangsan Fault, is characterized by a relatively rapid uplift (~0.4 mm/a) before the total unroofing of the pluton in the earliest Cretaceous (~140 Ma) followed by a subsidence (~0.2mm/a) during the Hayang Group sedimentation. Stability of original FT zircon ages (156 Ma) and complete erasure of apatite ages suggest a range of 3 to 5.5 km for the basin subsidence. Since 120 Ma up to present, the Yeongyang Subbasin has been slowly uplifted (~0.04 mm/a). The FT age patterns of Jurassic granites both from the northeastern wing of the Ryeongnam Massif and from the northern edge of the Pohang-Kampo Block indicate that the two geologic units have been slowly uplifted with a same mean rate (~0.04 mm/a) since early Cretaceous. Estimates of Cenozoic total uplifts since 100 Ma are different: Ryeongnam Massif (~6 km)=Pohang-Kampo Block (~6 km)>Yeongyang Subbasin(~4 km).

• Geosciences Journal
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• v.23 no.1
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• pp.1-20
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• 2019

We present data from the Mesozoic Keumkang, Palbong, and Baekhwa granites in Garorim Bay, in the southwestern part of the Gyeonggi massif, South Korea. Using major and trace element concentrations, Sr-Nd-Pb isotopic compositions, and sensitive high-resolution ion microprobe (SHRIMP) zircon U-Pb ages, we aim to constrain the petrogenesis of the granites and explain their origin within a broader regional geological context. SHRIMP U-Pb zircon ages of $232.8{\pm}3.2$, $175.9{\pm}1.2$, and $176.8{\pm}9.8$ Ma were obtained from the Keumkang, Palbong and Baekhwa granites, respectively. The Late Triassic Keumkang granites belong to the shoshonite series and show an overall enrichment in large ion lithophile elements (LILE), a depletion in high field strength elements (HFSE) relative to primitive mantle, compared with neighboring elements in the primitive mantle-normalized incompatible trace element diagram with notable high Ba and Sr contents, and negligible Eu anomalies. The Keumkang granites are typified by highly radiogenic Sr and unradiogenic Nd and Pb isotopic compositions: $(^{87}Sr/^{86}Sr)_i=0.70931-0.70959$, $(^{143}Nd/^{144}Nd)_i=0.511472-0.511484$ [$({\varepsilon}_{Nd})_i=-17.0$ to -16.7], and $(^{206}Pb/^{204}Pb)=17.26-17.27$. The Middle Jurassic Palbong and Baekhwa granites belong to the medium- to high-K calc-alkaline series, and show LILE enrichment and HFSE depletion similar to the Keumkang granites, but exhibit significant negative anomalies in Ba, Sr, and Eu. Furthermore, they have elevated Y and Yb contents at any given $SiO_2$ content compared with other Jurassic granitoids from the Gyeonggi massif. The Palbong and Baekhwa granites have slightly less radiogenic Sr and more radiogenic Nd and Pb isotopic compositions [$(^{87}Sr/^{86}Sr)_i=0.70396-0.70908$, $(^{143}Nd/^{144}Nd)_i=0.511622-0.511660$, $({\varepsilon}_{Nd})_i=-15.4$ to -14.7, $(^{206}Pb/^{204}Pb)=17.56-17.76$] relative to the Keumkang granites. The Keumkang granites are considered to have formed in a post-collisional environment following the Permo-Triassic Songrim orogeny that records continent-continent collision between the North and South China blocks, and may have formed by fractional crystallization of metasomatized lithospheric mantle-derived mafic melts. The Palbong and Baekhwa granites may have been produced from a gabbroic assemblage at pressures of less than ~15 kbar, associated with subduction of the paleo-Pacific (Izanagi) plate at the Eurasian continental margin. Elevated ${\varepsilon}_{Nd}(t)$ values in the granitoids from the southwestern part of the Gyeonggi massif relative to those of the central and northern parts, together with the comparatively shallow depth of origin, imply the presence of an exotic block in the Korean lithosphere.

• Economic and Environmental Geology
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• v.5 no.4
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• pp.231-239
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• 1972

The central region of South Korea is composed of Precambrian formations and Jurassic Daebo granites and is divided tectonically into three provinces, that is, the Ok chon geosynclinal zone in the middle, the Kyonggi massif on the north and northwest side, and the Ryongnam massif on the south and southeast side. The general trend of the Okchon geosynclinal zone and the distribution of Daebo granites is northeast, the Sinian direction. The Kyonggi massif is composed of Precambrian Y onchon system, Sangwon system, gneisses, and Daebo granites, and the Ryongnam massif also Precambrian Ryongnam and Yulri systems, gneisses, and Daebo granites. Precambrian formations in both areas are of flysch type sediments and may be roughly correlated with each other. These formations except Sangwon and Yulri systems are thought to be early to middle Precambrian age and have acted as basement for the Okchon geosyncline where late Precambrian Okchon system was deposited. The Okchon geosynclinal zone is divided into paleogeosynclinal zone to southwestern parts where the Okchon system is distributed, and neogeosynclinal zone to northeastern parts where nonmetamorphosed Paleozoic sediments are dominantly cropped out. Both zones are separated by upthrust created by Daebo orogeny of Jurassic period, which continues southwesterly to bind the Okchon geosynclinal zone and the Ryongnam massif at southwestern parts bisecting Korea peninsula diagonally. Three periods of structural development are recognized in the area. Folds and faults of preTriassic age prevail in the Kyonggi massif. Many isoclinal folds and thrusts originated by Jurassic Daebo orogeny are aligned in the Okchon paleogeosynclinal zone paralleling to the geosynclinal axis so that same formation appears repeatedly in narrow strips, whereas fold axis in neogeosynclinal zone trerid west-northwesterly which might be of Triassic in age and modified by later Daebo orogeny. Discontinuity of geology and structure of Okchon geosynclinal zone is attributed to shifting of the geosyncline through geologic time.

• Economic and Environmental Geology
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• v.4 no.1
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• pp.1-9
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• 1971

The "Younger Granites" in Korea were being believed to be late Cretaceous in age and named "Bulkuksa granites" by all previous works until the writer had discovered Jurassic granite in 1963. The present paper is to prove its validity by age dating on these granites which was carried out by Professor Y. Ueda, Tohoku University, Japan. The age of 37 granites samples from various localities ranges from 68 my to 181 my. Of these 10 samples belonged to early Jurassic, 6 samples to mid-Jurassic, 4 samples to late Jurassic, 5 samples to early Cretaceous, and 12 samples to late Cretaceous in age. It is of the writer's opinion that the granites intruded in from early Jurassic to early Cretaceous age belong to Daebo granites and are syntectonic plutons associated with Daebo orogeny, and only those of late Cretaceous age belong to Bulkuksa granites that were associated with Bulkuksa disturbance. Daebo granites are aligned along NE-SW Sinian direction in the middle parts of Korea and crop out in the cores of folded mountains which were formed by Daebo Orogeny, such as Charyong, Noryong, Sobaek, and Dukyu Ranges. On the contrary Bulkuksa granites are restricted in Kyongsang basin and adjacent few localities in distribution and show no alignment. Granites supposedly associated with other disturbances of post-precambrian Have not been found so far in S. Korea. Age dating of granites has revealed that Daebo orogeny might be continuous from Songrim distur bance of late Triassic age. From this viewpoint, it could be assumed that Daedong system of Jurassic age were deposited in separate intermontain basins while Daebo orogeny was active, so that Daedong system in separate localities in Korea could not been correlated in their lithology as well as stratig raphy.

• Economic and Environmental Geology
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• v.23 no.1
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• pp.87-104
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• 1990

Foliated granites between Damyang and Jinan are subdivided into Daegang foliated granite, Foliated hornblende biotite granodiorite, Sunchang foliated granodiorite, Foliated two mica granite and Samori foliated granite by mineral and texture. From EPMA data of the foliated granites following results are achieved. Composition of plagioclase are correspond to andesine, oligoclase and albite in Foliated hornblende biotite granodiorite, Sunchang foliated granodiorite and other foliated granites, respectively. And amphiboles are calcic hornblende in Foliated hornblende biotite granodiorite, and riebeckite in Daegang foliated granite. In differentiation index(D. I.) and Larsen index(L. I.), Daegang foliated granite, Foliated two mica granite and Samori foliated granite which belong to granite are 83.12-95.54 and 25.86-29.05 and Foliated hornblende biotite granodiorite and Sunchang foliated granodiorite of diorite to granodiorite are 54.99-78.54(D. I.) and 6.48-21.01(L. I.). Harker and AMF diagrams plotted from foliated granites show that the granites are product of calc alkali rock series orignated from co-magma. Characteristic foliation of foliated granites fromed by ductile deformation at deep zone of dextral strike slip fault. Foliated granites are considered as a series of differentiated product of Triassic Igneous activity of Songrim disturbance. According to REE, (La/Lu) and Eu/Sm, Foliated hornblende biotite granodiorite and Sunchang foliated granodiorite are correspond to granodiorite, and other foliated granites are monzo-and syeno-granite. Foliated granites having 0.20-0.01 of Em/Sm ratio are plutons emplaced by the tectonic setting in continents and continental margin.

• Economic and Environmental Geology
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• v.26 no.1
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• pp.83-96
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• 1993

Kwangju granite body located in vicinity of Kwangju city consist of three rock bodies-Kwangju rock body, Jangsung rock body and Youngkwang rock body. Petrochemistry of Kwangju granite is as follows: Kwangju granite body is igneous complex which compose of a series of differential products of a magma. Kwangju granites are divided into four rock facies based on the geologic age, mineralogical and chemical constituents and texture: Triassic hornblende-biotite granodiorite and biotite granite, and Jurassic porphyritic granite and two mica granite. Harker and other variation diagrams of Kwangju granites plot on trend of calc-alkali rock series and range of peraluminous granite. Parental magma type of Kwangju granites correspond to I-type, Syn-Collision type in compressive stress field by collision movement between both rock block. In chondrite normalized REE patterns of Kwangju grnites, LREE enriched than HREE in REE amount and have more steep negative slope with slightly (-) Eu anormaly.

• The Journal of the Petrological Society of Korea
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• v.23 no.4
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• pp.393-403
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• 2014

U-Pb ages were determined from the Yongyudo biotite granites from western parts of Gyeonggi massif. The results show that the emplacement age of the Yongyudo biotite granite is ca. 227-230 Ma. Such age result that is somewhat older than previous reported ages, suggesting further investigations for the timing and evolution of the Jurassic granites of the western Gyeonggi massif.