• The Journal of the Petrological Society of Korea
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• v.13 no.1
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• pp.16-33
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• 2004

By relating mineralogy, petrology and geochemistry to observed magnetic properties, an understanding of the geological factors that control magnetic signatures is obtained. Magnetic susceptibility measurements and geochemical analyses were carried out for 160 samples in the Jurassic to Cretaceous granitoids, which is distributed to Pocheon, Jipori, Geumsan, Namwon, Songnisan, Yongdam, Masan, Jindong, and Taebaeksan areas. The magnetic properties of igneous infusion in these granites reflect bulk rock composition, reduction-oxidation state, hydrothermal alteration which are controlled by tectonic setting, composition and history of the source region, depth of emplacement and nature of wall rocks.

• Economic and Environmental Geology
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• v.25 no.4
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• pp.463-477
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• 1992

The study area consists of sedimentary and volcanic rocks of Gyeongsang Supergroup, granitoid intrusives, and hornfelses around the granitoids. Granitoid intrusives occur in small stocks in Nijeon-ri, Uggogri, and Yul-ri area. The masses in Nijeon-ri and Uggog-ri are hornblende-biotite granodiorite, biotite granodiorite respectively, and Yul-ri mass is biotite granite. Surrounding sediments of these masses were thermally metamorphosed and contact aureoles were formed. The studied granitoids are considered to be formed by sequential crystallization-differentiation from calc-alkalic granitoid magma. Metamorphic minerals occurring in contact aureole are chlorite, actinolite, epidote, and biotite. Diopside and hornblende are observed in small amount in some lithology around contact aureole. The lithology of contact aureole is predominantly silty and sandy, and characteristic metamorphic minerals were poorly developed because of low temperature metamorphism. Low temperature in contact aureole could be deduced from the facts that the intrusions were small size, shallow depth, low temperature, and rare movement of volatiles from magma.

• Economic and Environmental Geology
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• v.17 no.3
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• pp.179-195
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• 1984

The Jurassic Daejeon and Nonsan granitoids are "S-type" syntectonic calc-alkaline two-mica monzogranite and granodiorite, respectively. With evidences of high CaO, $Al_2O_3$, LIL/HFS elements, total REE, (Ce/Yb)N and initial ($^{87}Sr/^{88}Sr$) ratio, and no significant Eu anomaly, the primary magmas for the Daejeon and Nonsan granitic rocks are derived from partial melting of the Precambrian granulite (e.g. grey gneisses). But those Jurassic granitoids crystallised from different chemical characteristics of parental magmas which is mainly due to varying degree of partial melting of the granulite (crustal anatexis). The absence of significant anomalous Eu($Eu/Eu^*=O.82{\sim}1.00$) in the Daejeon and Nonsan granitoids could indicate that feldspars, mainly plagioclase, did not separate from the magmas. The parental hydrous magmas could not rise appreciably above their source region before crystallisation. The Jurassic granitoids may be resulted by closing-collision situation and belong to the Hercynotype (Pitcher 1979) such as compressive ductile regime of an intracontinental orogen.

• Economic and Environmental Geology
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• v.23 no.2
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• pp.245-259
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• 1990

Petrochemical analyses of granitic rocks including trace element, REE and oxygen isotope were carried out to understand petrogenesis of plutonic rocks from the Chungju, Wolaksan and Jecheon granite batholiths, which might be related with tungsten-base metal-fluorite mineralization in the Hwanggangri metallogenic province. Different geochemical characteristics such as major and trace elements were found between Jurassic Daebo granitic rocks (Chungju, Jecheon, Wonju, and Boeun granitic rocks) and Cretaceous Bulgugsa granitic rocks (Wolaksan, Muamsa and Sokrisan granitic rocks). Cretaceous granitoids are characterized by high $SiO_2$and $K_2O$ contents and low $TiO_2$, $Al_2O_3$, MgO and CaO contents. They also have relatively high contents of trace elements(Zn, V, Co, Cr, Sr, and Ba) in comparison with the Jurassic granitoids. (Eu)/($Eu^*$) and $(La/Lu)_{CN}$ ratios of Jurassic plutons vary from 0.78 to 1.13 and from 26.02 to 30.5, respectively, while the ratios of Cretaceous ones range from 0.22 to 0.28 and from 4.42 to 14.2, respectively. The REE patterns of the Cretaceous and Jurassic granitic rocks have quite different Eu anomalies: large negative Eu anomaly in the former, and mild or absent Eu anomaly in the latter. The large Eu negative of Cretaceous granitic rocks are interpreted as a differentiated product of fractional crystallization of granitic magma deduced by Rayleigh fractionation model(Tsusue et al., 1987). Oxygen isotopic compositions of quartz for Daebo and Bulgugsa granitic rocks range from 9.98 to 10.51‰ and from 8.26 to 9.56‰, respectively. The Daebo granitic rocks enriched in $^{18}0$ suggest that the magma be undergone different partial melting processes from the Bulgugsa ones. Of the Bulgugsa granitoids, Wolaksan and Sokrisan mass have different contents of trace elements and ${\delta}\;^{18}0$ values of the silicate minerals, which indicate that they are not from the identical source of magma. Many mineral deposits are distributed in and/or near the Wolaksan and Muamsa granitic rocks, but a few mineral deposits are found in and near the Chungju and Jecheon granite batholiths. It might be depend on geochemisty of the related igneous rocks which have low contents of Ba, Sr, Co, V, Cr, Ni, Zn and high contents of Nb and Y, and on lithology of country rocks such as cabonate and noncarbonate rocks.

• Journal of the Korean earth science society
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• v.18 no.6
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• pp.480-492
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• 1997

In order to understand the processes involved in the petrogenesis and the differentiation of the primary magma spectrum, a petrological and geochemical properties were investigated for the Chonju and the Sunchang foliated granites, which are located in the southwestern part of the Okchon zone and extends up to the northwestern boundary of the Ryongnam massif as two subparallel batholiths. Major element analyses show that the Chonju and Sunchang foliated granites are classified petrologically into a weakly to strongly peraluminous or calc-alkaline, but do not fit neatly into either of the I/S-type or magnetite/ilmenite-series classification schemes for granites, although the I-type and magnetite-series characteristics seem to be predominant based on the major element chemistry. In normative compositions, the Chonju granite is petrographically evolved from granodiorite to granite, whereas the Sunchang granite is from granodiorite to quartz monzodiorite. It seems to suggest a difference of the magmatic evolution processes such as crustal assimilation and/or fractional crystallization in magma. The REE patterns of both batholiths show high similarity and strongly fractionated REE distributions which show high $(Ce/Yb)_N$ ratios and little or no Eu anomalies. These REE patterns correspond broadly to those seen in the pre-Cretaceous granitoids of Korea. Apparently, the evidences obtained from the bulk compositions strongly suggest that the two foliated granitoids were formed by partial meltings of a relatively restricted and similar, may be common, source material which contains a continental crust component having an igneous composition, and have undergone a similar magmatic differentiation processes.

• Economic and Environmental Geology
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• v.39 no.5 s.180
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• pp.567-581
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• 2006

The Au-Ag lode deposits in South Korea are closely associated with the Mesozoic granitoids. Namely, the Jurassic deposits formed in mesozonal environments related to deep-seated granitoids, whereas the Cretaceous ones were developed in porphyry-related environments related to subvolcanic granitoids. The time-space relationships of the Au-Ag lode deposits in South Korea are closely related to the changing plate motions during the Mesozoic. Most of the Jurassic auriferous deposits (about $165{\sim}145$ Ma) show fluid characteristics typical of an orogenic-type gold deposits, and were probably generated in a compressional to transpressional regime caused by an orthogonal to oblique convergence of the Izanagi Plate into the East Asian continental margin. On the other hand, strike-slip faults and caldera-related fractures together with subvolcanic activity are associated with major strike-slip faults reactivated by a northward (oblique) to northwestward (orthogonal) convergence, and probably have played an important role in the formation of the Cretaceous Au-Ag lode deposits (about $110{\sim}45$ Ma) under a continental arc setting. The temporal and spatial distinctions between the two typical Mesozoic deposit styles in South Korea probably reflect a different thermal episodes (i.e., late orogenic and post-orogenic) and ore-forming fluids related to different depths of emplacement of magma due to regional changes in tectonic environment.

• The Journal of the Petrological Society of Korea
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• v.25 no.2
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• pp.121-142
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• 2016

The Satkatbong pluton was studied with other plutons together, but some fundamental petrological characteristics were missing. This study mainly reports the petrography and geochemistry of the Satkatbong pluton comparing with the Daebo and the Bulguksa granitoids in south Korea. The Satkatbong pluton, which is host rock including a number of Mafic Magmatic Enclaves (MME), is north-south shaped dioritic pluton, located along the east coast of south Korea. The Satkatbong pluton seems to be unconformable with Cretaceous sedimentary rocks from fieldwork result. In geochemistry, the Satkatbong pluton, which is roughly similar with the Daebo granitoids, is classified into calc-alkali series rock and volcanic arc granitoid Tectonically. The fact that AlT value in marginal parts of amphiboles in the Satkatbong pluton is lower than other granitoids implies emplacement depth of the Satkatbong pluton was relatively shallow. The Satkatbong pluton shows different geochemical feature compared to the adjacent adakitic Yeongdeok granite. This seems to be caused by mafic mantle material expected from the occurrence of MMEs.

• Journal of the Mineralogical Society of Korea
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• v.18 no.3 s.45
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• pp.215-225
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• 2005

Numerous clay veins along fractures such as fault, joints, cracks and small fissures are found in granitic rocks in the Korean Peninsula. Granitic rocks of three geological stages (Jurassic, Cretaceous and Paleogene) occur in the Korean Peninsula, and are known as the Daebo, Bulguksa and Hoam granites, respectively. Specimens from clay veins composed or mainly mica clay mineral (illite) were dated using the K-Ar method with the hosted granitoids. The respective ages were as follows. Jurassic: granites 143.7 Ma and 160 Ma, clay mineral veins 104 Ma and 107 Ma: Cretaceous: granite 133.2 Ma, clay mineral veins 93.6 Ma, 84.2 Ma and 84.3 Ma: Paleogene: granite 39.7 Ma and 35.4Ma, clay mineral veins 27.1 Ma and 23.9 Ma. The ages of the clay veins in the Korean Peninsula are clearly much younger than those of their hosted granitoids. This contrasts with data for similar clay veins in Cretaceous and Paleogene granitoids in southwest Japan, where the K-Ar ages of mica clay minerals are slightly younger than their host rocks, or are almost the same.

• The Journal of the Petrological Society of Korea
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• v.23 no.3
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• pp.279-292
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• 2014

Nd isotopic compositions analyzed from the Phanerozoic granitoids of Korea are integrated and discussed. Variations in Nd isotopic compositions can be explained either by temporal trend or by regional differences. Among the three active periods, first two periods during the Permian-Triassic and Jurassic seem to show variations from rather high ${\varepsilon}_{Nd}(t)$ values at the beginning to lower ${\varepsilon}_{Nd}(t)$ values during the later stages. Such trends probably reflect melting of the subducting oceanic crust and producing magma with higher proportion of depleted mantle derived materials during the early stage of subduction process, and subsequent magmas with greater proportion of old continental crust with progress of subduction. However, the Cretaceous-Paleogene period of active magmatism displays higher ${\varepsilon}_{Nd}(t)$ values during the advanced stage of the igneous activities, which is opposite to the previous active periods. The other explanation is that such differences in ${\varepsilon}_{Nd}(t)$ reflect regional differences, based on the observations that such high-${\varepsilon}_{Nd}(t)$ granitoids distribute in the northeastern Gyeongbuk Province and Gyeongsang Basin. If this is the case, the regions with highr ${\varepsilon}_{Nd}(t)$ values may have distinct crustal evolution histories, e.g. younger average age. The choice between the two hypothesis could be made through further studies.

• Proceedings of the KSEEG Conference
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• 2003.04a
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• pp.189-190
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• 2003

Oxygen and hydrogen isotopic data of whole rocks and mineral separates generally provide constraints on the nature of hydrothermal systems. We here report preliminary results of analyses of samples taken from the peraluminous granitic rocks and banded gneiss country rocks in Hwacheon area. Oxygen isotopic values for quartz and feldspar separates from the granitoids in Hwacheon area range from 8.2 to 10.6$\textperthousand$ and 5.8 to 8.5$\textperthousand$, respectively. (omitted)