• The Journal of the Petrological Society of Korea
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• v.5 no.1
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• pp.35-51
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• 1996

The granitic rocks in the vicinity of the Mt. Sorak, the northeastern part of the NE-SW elongated Mesozoic granitic batholith in the Kyeonggi massif, consist of granodiorite, biotite granite, two-mica granite and alkali feldspar granite. Variations In major and most trace elemental abundances show a typical differentiation trend in a granitic magma. Granitic rocks all display a calc-alkaline trend in the AFM diagram. Also, In the ACF diagram discriminating between I- and S-type granitic rocks, granodiorite and most biotite granite in the southeastern area represent I-type and magnetite-series characteristics, while most biotire granite and two-mica granite in the northwestern area exhibit S-type and ilmenite-series ones.According to recent studies of the granitle rocks In the Inje-Hongcheon district. all ihe granitic rocks distributed in the northeastern part of the Kyeonggi massif have been classified as late Triassic to early Jurassic Daebo granite. With reference of the formerly published ages, an age oi $125.6{\pm}4.4$ Ma calculated by the slope in the plot of $^{87}Rb/^{86}Sr-^{87}Sr/^{86}Sr$ for the biotite granite samples from the southeastern area is inferred as an emplacement age for the granitic rocks in the vicinity of the Mt. Sorak. On the basis of elemental variations and Sr isotope compositions, an possible evolutional process for the granitic magmas in this area is suggested. The primary magma of I-type and magnetite-series generated about 125 Ma by partial melting of igneous originated crustal materials, might be emplaced and evolved through fractional crystallization, convection and assimilation of the surrounding Precambrian metasediments to become S-type and ilmenlte-serles in the outer area, and then solidified to granodiorite, biotite granite and two-mica granite.At the latest stage, the evolved hydrothermal solution altered the formerly solidified biotite granite to alkali feldspar granite and probably later local igneous activities affected the alkali feldspar granite again.

• Economic and Environmental Geology
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• v.20 no.1
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• pp.35-60
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• 1987

The geochemical characteristics including minerals, major and trace elements chemistries of the Proterozoic, Jurassic and Cretaceous granites in Korea are systematically summarized and intended to decipher the origin and crystallization process in connection with the tectonic evolution. The granites in Korea are classified into three different ages of the granites with their own distinctive geochemical patterns: 1) Proterozoic granitoids; 2) Jurassic granites(cratonic and mobile belt); 3) Cretaceous-Tertiary granites. The Proterozoic granite gneisses (I-type and ilmenite-series) formed by metamorphism of the geochemically evolved granite protolith. The Proterozoic granites (S-type and ilmenite-series) produced by remobilization of sialic crust. The Jurassic granites (S-type and ilmenite-series) were mainly formed by partial melting of crustal materials, possibly metasedimentary rocks. The Cretaceous granites (I-type and magnetite-series) formed by fractional crystallization of parental magmas from the igneous protolith in the lower crust or upper mantle. The low temperature ($315{\sim}430^{\circ}C$) and small temperature variations (${\pm}20{\sim}30^{\circ}C$) in the cessation of exsolution of perthites for the Proterozoic and Jurassic granites might have been caused by slow cooling of the granites under regional metamorphic regime. The high ($520^{\circ}C$) and large temperature variations (${\pm}110^{\circ}C$) of perthites for the Cretaceous granites postulate that the rapid cooling of the granitic magma. In terms of the oxygen fugacity during the feldspar crystallization in the granite magmas, the Jurassic mobile belt granites were crystallized in the lowest oxygen fugacity condition among the Korean granites, whereas the Cretaceous granites in the Gyeongsang basin at the high oxygen fugacity condition. The Jurassic mobile belt granites are located at the Ogcheon Fold Belt, resulting by closing-collision situation such as compressional tectonic setting, and emplaced into a Kata-Mesozonal ductile crust. The Jurassic cratonic granites might be more evolved either during intrusion through thick crust or owing to lower degree of partial melting in comparison with the mobile belt granites. The Cretaceous granites are possibly comparable with a continental margin of Andinotype. Subduction of the Kula-Pacific ridge provided sufficient heat and water to trigger remelting at various subcrustal and lower crustal igneous protoliths.

• 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.

• Economic and Environmental Geology
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• v.19 no.2
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• pp.97-107
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• 1986

The Cretaceous Imog granite is a calc·alkaline, subsolvus monzogranite and shows characteristics of "I-type" and "magnetite·series" granite by mineralogy and chemical composition. Many of the major and trace element characteristic of the Imog granite are consistent with a relationship by fractional crystallization of a basic magma. The primary magma of the granite derived from the subduction of oceanic crust at the destructive plate margin. The granite shows light REE enrichment with (Ce/Yb)N ratios of 7.77~12.55. All the REE patterns show Eu negative anomalies ($Eu/Eu^*=0.69$) in the pluton. The Imog granite at the southwestern part of the Hambaeg basin may be intruded along the tectonic intersections of the E-W and N-S lines such as deep faults and fractures. Radiometric age determination on the granite reveals as $96.7{\pm}2.0Ma$ by K-Ar dating on biotite.

• The Journal of the Petrological Society of Korea
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• v.8 no.2
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• pp.57-70
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• 1999

The volcanic rocks of Ulleungdo reveal very high alkali element abundances and most of them have high K20/Na20 ratios and belong to potassium-series. Ulleungdo volcanics show very wide range of variation in their composition from basalts to trachytic basalt, basaltic trachyandesite, trachyandesite, and finally to trachyte on total alkali-silica diagram. Such a general trend of compositional variation can be explained well by differentiation due to fractional crystallization of various minerals. Olivine, clinopyroxene, plagioclase, ilmenite, and apatite are suggested as the major fractionated minerals. Ulleungdo volcanics show Nb/U and PbICe ratios similar to oceanic volcanics such as MORB and OIB, but significantly different .from volcanic rocks of island arc environments, which suggest that they are not directly related with subduction along the Japanese arc. LREE abundances of Ulleungdo volcanics are highly enriched compared with HREE abundances ((La)N=193-420, (L~)~=7.5-19.5).O nly trachyte-1 show appreciable negative Eu anomalies among various rock types, which suggests significant amount of plagioclase were fractionated. However, trachyte-2, trachyte-3, phonolite, and pumice reveal quite different variation trend of trace and rare earth element abundances from trachyte-1, which suggest that they have originated from different magma batches and have experienced different differentiation processes. A prominent bimodal distribution, thus lacking of intermediate composition, is observed from the Ulleundo volcanics.

• The Journal of the Petrological Society of Korea
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• v.9 no.3
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• pp.169-186
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• 2000

The Miocene volcanic rocks in the Dangsari area, eastern part of Ulsan city, are mainly composed of andesite lava flows and pyroclastic rocks. The andesite lavas are identified as two-pyroxone andesite, comprising phenocrysts of augite ($Wo_{43.2}$ $En_{41.0}$ $Fs_{15.8}$ ) and hyperthene ($Wo_{2.7}$ $65.8_{En}$ $_{Fs}$ 31.5). The andesitic pyroclastic rocks are largely composed of pyroclastic breccias with alternating tuff-breccia and lapilli tuff, which showing planar layering, and minor amount of andesitic tuff with thin deposits of interlayered tuffaceous shale. According to the petrochemical data, andesitic rocks belong to medium-K calc-alkaline andesite. The position of bulk composition on the AFM diagram and the presence of normative quartz and hypersthene indicate that the volcanic rocks are calc-alkaline. The trace element composition and REE patterns of andesite, which are characterized by a high LILE/HFSE ratio and enrichment in LREE, suggest that they are typical of continental margin arc calc-alkalic volcanic rocks produced in the subduction environment. On the discrimination diagram, the Dangsari volcanic rocks fall into the fields of subduction related continental margin arc volcanic province. The primary magic melts may be derived from about 15% partial melting of mantle wedge in the upper mantle under destructive plate margin. And the melt evolved to calc-alkaline andesite magma by fractional crystallization and the magma was a little contaminated with crustal materials.

• 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.

• The Journal of the Petrological Society of Korea
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• v.6 no.3
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• pp.166-184
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• 1997

The Wondong caldea is a deeply eroded structure that offers spectacular exposures through the core and margins of a resurgent caldera. The Wondong Tuff and the postcollapse intrusions range from medium-silica rhyolite to rhyodacite in composition and the postcollapse lava and tuff, preresurgent and resurgent intrusions also range from medium-silica rhyolite to an-desite, which jump to gap dacite composition. The continuous compositional zonations generally define a large stratified magma system in the postcollapse and resurgent magma chamber. Isotopic and trace element evidence suggest that the compositional zonations might have resulted from the differentiations from crystal fractionations of a parental andesitic magma, accompanying a little contamination from the crustal assimilations near the chamber roof and wall. But chemically and isotopically distinct late intusions might have resulted from emplacement of any different magma batch.

• The Journal of the Petrological Society of Korea
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• v.6 no.1
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• pp.1-18
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• 1997

Andesitic pyroclastics and lava flows are deposited as a part of composite volcanoes by Cretaceous volcanic activity in Geojae Island, off the coast of Korea. The andesitic pyroclastics are composed of tuff breccia and lapilli tuff minor intercalated tuff. Lava flows are divided into dense and porphyritic andesite containing phenocrysts of plagioclase, pyroxene, and/or hornblende. The andesitic rocks represent charactersitcs of carc-alkaline BAR association with basalt, basaltic andesite, andesite, and dacite to rhyolite. Major element variations of the volcanic rocks show that $Al_2O_3$, total FeO, CaO, MgO and $TiO_2$ decrease with increasing $SiO_2$ but $K_2O$ and total alkalis increase, and represent differntiation trend of calc-alkaline rock series. In spider diagram, contents of Sr, K, Rb, Ba, and Th are relatively high, but contents of Nb, P, Ti and Cr are low. These petrochemcial characteristics are similar to those of rocks from island arc or continental margein related to plate subduction. Chondrite-normalized REE patterns of volcanic rocks are paralle to subparallel, with LREE enriched than HREE, and show gradual increase of negative Eu anomaly from basalt to dacite and rhyolite, suggesting comagmatic fractional crystallization with minor effects of assimilation and magma mixing. Andesitic rocks are assumed medium-K orogenic andesites that formed in the tectomagmatic environment of subduction zone under normal continental margin arc.

• The Journal of the Petrological Society of Korea
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• v.7 no.1
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• pp.27-36
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• 1998

The volcanic piles in the northern Yucheon Minor Basin area are the Hagbong basaltic rocks, the Chaeyaksan basaltic rocks, the Jusasan andesitic rocks, the Unmunsa rhyolitic rocks, and the Tertiary voicanics. Stratigraphically, from the lowermost, (1) the Hagbong basaltic rocks are composed mainly of basaltic tuff with two olivine basalt flows intercalated, (2) the Chaeyagsan basaltic rocks are predominantly in tuffs and agglomerate with 3 basaltic flow interlayers, (3) the Jusasan andesitic rocks consist of thick piles of alternated sequences of 4 andesite flows and 5 andesitic tuffs and tuffaceous sediments and (4) the Unmunsa rhyolitic rocks which embed some rhyolite and obsidian are dominant in tuffs such as ash flow and crystal welded tuff. These volcanics reveal distinguishable characteristics in petrochemistry. In discriminating by major elements, the Hagbong and the Chaeyagsan basaltic rocks are alkaline, whereas the latter is also spilitic. In comparison, the volcanic rocks of the Jusasan andesitic rocks and the Tertiary sequences are characteristically calc-alkaline although their distribution is spatially separated. On the other hand, the variations in immobile trace elements indicate that the Hagbong basaltic rocks range from alkaline to calc-alkaline and from WPB/VAB transition to VAB, whereas the Chaeyagsan basaltic rocks are calc-alkaline WPB/VAB transition type and the two others calc-alkaline VAB. In order to show such a variety in their rock series of the volcanic rocks, the environment during their magma generation, magma rising, and post-eruption alteration could be positively considered.