• Tunnel and Underground Space
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• v.26 no.4
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• pp.266-273
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• 2016

We have numerically modeled thermal evolution of Ulleung Island after an emplacement of magma chamber. The disk-shape magma chamber is assumed to locate at 2.9 km beneath the island and has a diameter and a thickness of 10 km and 300 (or 600) m, respectively. The geothermal gradients evaluated from the numerical modeling coincide well with the range of the geotherms (${\sim}95^{\circ}C/km$) observed from the well logging. Although there are limitations in the application of the numerical results directly to the interpretation of the observed geotherms, we believe that an existence of a hot magma chamber in molten or in solidified state is the most plausible explanation for the observed geotherms.

• The Journal of the Petrological Society of Korea
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• v.9 no.3
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• pp.142-168
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• 2000

The granites distributed in the Kyongsang basin contain the rocks which are different from the host rocks, and they are known as magic microgranular enclaves. The genesis of the magic micro-granular enclaves can be divided into four types: (1) rock fragments from country rocks; (2) cumulation of the early crystals in host magma or disruption of early chilled borders; (3) magma mingling; and (4) restite. These enclaves can be easily found in the granites around Mt. Wonhyo, Yangsan city. They are ellipsoidal in shape, and have phenocrysts might be originated from the host rocks and sharp contacts with the granites. Under the microscope, textures such as oscillation zoning, horn-blende-mantled quartz, rapakivi texture, and acicular apatite are observed, and these indicate that the enclaves were originated from magma and then produced by chilling. The evidences showing that the enclaves were formed by magma mingling are: (1) petrographical characteristics; (2) similarity of the compositions between the rim of plagioclase in the enclave and plagioclase in the granite; (3) linear trends of the major elements; (4) total REE content of the enclaves; and (5) Textural and compositional variations from rim to core in zoned enclaves. The magic end member of the enclave is regarded as the aphyric basaltic andesite in Mt. Sinbul-Youngchui area. The granites around Mt. Wonhyo experienced the magma mingling process which was produced by the injection of mafic magma at about 70 Ma, during the crystal differentiation, and then continued the crystallization. The equigranular granites and the micrographic granites in the study area are considered as the results after the magma mingling process.

• Economic and Environmental Geology
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• v.33 no.1
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• pp.1-18
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• 2000

Lens shaped and stratiform titanomagnetite orebodies in the Boreumdo iron mine are closely associated with amphibolite which intruded into Precambrian metasediments. Mineralogical and petrochemical analyses of amphilbolite and titanomagnetite ores were carried out in order to interpret the origin of amphilbolite and the genesis of titanomagnetite ore deposits. Amphibolites belong to orthoamphilbolite interms of Niggli value and mineralogy, and are characterized by the occurrence of relict olivine. The amphilbolites responsible for titanomagnetite mineralization have extremely high content of $TiO_2$, ranging from 2.12 to 4.59 wt.% with the average value of 3.43 wt.%. Amphibole minerals in amphibolites are consist mainly of calcic amphiboles such as hornblende, ferroan pargasitic hornblende and tremolite. Most plagioclases belong to andesine ($An_{30-50}$\ulcorner). The metamorphic temperature and geobarometric pressure which are calculated by the calcic amphibole-plagioclase geothermometer and calcic amphilbole geobarometer are estimated to be 537$^{\circ}C$~579$^{\circ}C$(avg. 555$^{\circ}C$) and 2.9~6.6 kbar (avg. 4.5 kbars), respectively. It shows a typical amphibolite facies. Based on the mineral chemistry and petrochemisty of amphibolites and iron ores which are composed mainly of titanomagnetite and ilmenite in the Boreumdo iron mine, the titaniferous oxide melts could be immiscibly separatd from the titaniferous ultrabasic magma. The genesis of the Boreumdo titanomagnetite ore deposits are analogous to the Soyeonpyeongdo and Yonchon iron ore deposits in terms of their mineralogy, mineral chemistry and geologic setting.

• The Journal of the Petrological Society of Korea
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• v.11 no.1
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• pp.30-48
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• 2002

Phenocrysts with rapakivi texture are easily observed in Bangeojin granite. The rapakivi texture is composed of inner pinkish alkali feldspars and white-colored mantling plagioclase. The Bangeojin granite distinctively includes lots of mafic microgranular enclaves and can be divided into five rock facies: (1) enclave-poor granite (EPG); (2) enclave-rich granite (ERG); (3) mafic microgranular enclave (MME); (4) hybrid zone between mafic microgranular enclave and granite (HZ); (5) hybrid zone-like enclaves (HLE). The rapakivi textures are observed in these five rock facies with no difference in shape and size. Plagioclase mantle commonly shows dendritic texture that is an important indicator to know the rapakivi genesis. The mantling texture would indicate supercooling condition during magma solidification process. In addition, mafic microgranular enclaves would imply the magma mingling environment. The magma mixing process had possibly caused the mantling texture. An abundance of rapakivi phenocrysts in HZ and the influxing phenomenon of the phenocrysts into MME support that there were physical chemical exchanges during the mingling. And this model of the magma mixing/mingling explain well the heterogeneous distribution of the rapakivi phenocrysts in the five rock facies. Therefore the rapakivi textures in the Bangeojin granite would have been formed by magma mixing process.

• The Journal of the Petrological Society of Korea
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• v.26 no.3
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• pp.183-200
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• 2017

Alkali rhyolites in the Cheonmunbong of the Mt. Baekdu stratovolcano show porphyritic texture in the glassy or aphanic groundmass. Major phenocryst is alkali-feldspar, pyroxene, and amphibole, and small amount of microphenocryst is olivine, quartz, opaque mineral (ilmenite). The content of $Fe^{2+}/(Fe^{2+}+Mg^{2+})$ and alkali elements in the mafic minerals is high. Alkali feldspar is classified as sanidine or anorthclase, olivine as fayalite, and pyroxene as ferro-hedenbergite of ferro-augite area. Amphibole belongs to alkali amphibole group, but FeO and $Fe_2O_3$ were not separated, so it is required future studies. Nb(-) anomaly suggesting that slab-derived materials might have played a primary role in the genesis of the rhyolite magma, is not observed. It is noted that they originated in the within plate environment which is not related to subduction zone of the convergent plate boundary. The Mt. Baekdu alkaline rocks are classified into the comendite series. The alkali rhyolites of the summit at Mt. Baekdu shows the disequilibrium mineral assemblages, suggesting that it evolved from thrachytic magma with experience of magma mixing as well as fractional crystallization.

• Ocean and Polar Research
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• v.25 no.1
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• pp.119-128
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• 2003

Although phoscorites and carbonatites form only a minor proportion of the earth's crustal rocks, these unusual rocks and their intimate relation are of both academic and economic importance. Rare metal (Nb, Zr, Ta) and REEs mineralizations are in close relation with the differentiation of these phoscorite-carbonatite complexes (PCCs). Recent integrated petrological and geochemical data on PCCs in the Kola Alkaline Province, Arctic, indicate that phoscorites and associated carbonatites are differentiated from common 'carbonated silicate patental magma'. Various hypotheses for the genesis of phoscorite-carbonatite complexes have been proposed during the last half-century. A simple magmatic fractionation scheme can not explain the chemical and mineralogical characteristics of phoscorite and conjugate carbonatite. Instead, the hypotheses involving liquid immiscibility and coeval accumulation processes are favored to explain the mineralogical and geochemical characteristics of phoscorite and carbonatite association.

• Journal of the Korean earth science society
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• v.28 no.3
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• pp.324-342
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• 2007

This study reports petrography and geochemical characteristics of the basalt lava flows in Seongsan-Ilchulbong area, the easternpart of Jeju island, Korea, to understand the evolutionary processes of magma. Basalt lavas are classified into the Pyoseon-ri basalt and the Seongsan-ri basalt. The Pyoseon-ri basalt is dark-gray colored with many vescicles, and mainly consists of olivine, feldspar and rarely of clinopyroxene as phenocrysts. The Seongsan-ri basalt is largely aphanitic basalt and bright-gray colored, divided into two lava-flow units: lower lava flow (B1) and upper lava flow (B2) by the intercalated yellowish lapillistone and paleosol. The lavas plotted into sub-alkaline tholeiitic basalt and alkaline basalt series. The tholeiitic basalts have characteristically higher $SiO_2,\;FeO^T$, and CaO contents, but lower $TiO_2,\;K_2O,\;P_2O_5$ and other incompatible elements compared to the alkali basalts. The tholeiitic basalts have higher $SiO_2$ to the same MgO contents than the alkalic basalts. The contents of Ni, Cr, and MgO show a strong positive correlation, which indicates that low-MgO phases like plagioclase and titanomagnetite were important during the differentiation of magma. The contents of incompatible elements against that of Th show a strong positive correlation. The chondrite-nomalized REE patterns of tholeiitic and alkalic basalts are subparallel each other. LREEs contents of the former are lower than, but HREEs contents are similar to the latter. They both are similar to their K/Ba ratios. The primitive-mantle normalized spider diagram demonstrates that the contents of Ba and Th of all basaltic magma are enriched, and yet Cr, Ni are depleted. The tholeiitic and alkalic basalts may be originated from a different degree of the partial melting of the same mantle material source, and one shows a higher degree of the partial melting than the other.

• Economic and Environmental Geology
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• v.27 no.4
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• pp.335-343
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• 1994

The Eonyang amethyst deposits are composed of vug quartz emplaced in the Eonyang granites of Mesozoic Cretaceous age. The Eonyang granites are composed of biotite granite, porphyritic biotite granite, aplite and miarolitic granite. The petrochemical data of the Eonyang granites show the trend of subalkaline magma, calc-alkaline magma, I-type granitoid and magnetite series. The vug quartz show the characteristic growth zoning (white quartz-smoky quartz-amethyst) from wall side. Generally fluid inclusions in the vug quartz can be divided into four main types based on compositions (I-type: gas inclusion, II-type: liquid inclusion, III-type: polyphase inclusion, IV-type: liquid $CO_2$-bearing inclusion). Solid phase of polyphase inclusions are halite(NaCl), sylvite(KCl), hematite ($Fe_2O_3$) and unknown anisotropic solid. Homogenization temperatures inferred from the fluid inclusion study ranges from $440^{\circ}C$ to $485^{\circ}C$ in white quartz, from $227^{\circ}C$ to $384^{\circ}C$ in smoky quartz, from $133^{\circ}C$ to $186^{\circ}C$ in amethyst, respectively. Salinities of fluid inclusions in each mineralization stages ranges from 40 wt.% to 58 wt.% in white and smoky quartz, from 1.0 wt.% to 8.7 wt.% in amethyst respectively. A consideration of the pressure regime during vug quartz deposition based on the boiling evidence suggests lithostatic pressure of less than 72 bars. This range of pressure indicate that vug quartz lay at depth of 750 m below the surface at the during mineralization.

• The Journal of the Petrological Society of Korea
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• v.14 no.3 s.41
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• pp.169-179
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• 2005

Acidic metavolcanic rocks distributed around the Chungju iron deposit show significantly high abundances of rare earth elements and high field strength elements. Relatively high ${\epsilon}_{Nd}$(0) values and lack of negative Nb anomaly suggest that assimilation of crustal material is not involved in their generation. They are plotted within the within-plate environment according the tectonic discrimination diagrams. Such geochemical characteristics are very similar to the acidic metavolcanic rocks of Munjuri Formation. They also show geochemical characteristics of Al-type magma of Eby (1992). All such diagnostic characters indicate differentiation of mantle-derived magma produced from the rift environment, related to the breakup of continent. In contrast to the alkali granites and the rare metal deposit both having age of c. 330 Ma, Sm-Nd isotopic data of the acidic metavolcanic rocks do not form well defined isochron. However, the alkali granites reveal low ${\epsilon}_{Nd}$(0) values, while the acidic metavolcanic rocks and the rare metal deposit both have significantly higher ${\epsilon}_{Nd}$(0) values. Considering such differences, we propose following generation hypothesis: The acidic metavolcanic rocks around Chungju iron deposit was erupted at 750 Ma as rest of the acidic metavolcanic rocks of Gyemyeongsan and Munjuri Formations. About 330 Ma ago, partial melting of existing Al-type igneous materials and some old crustal materials produced alkali granite. The rare metal deposit was also produced by redistribution of related materials within the acidic volcanics due to hydrothermal activities occurred at the same time. Sm-Nd isotopic systematics of the acidic metavolcanic rocks were disturbed during the regional metamorphic event at ca. 280 Ma.

• Economic and Environmental Geology
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• v.26 no.3
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• pp.289-309
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• 1993

Milyang pyrophyllite deposit which was formed by hydrothermal alteration occurs in Late Cretaceous andesitic tuff in the Milyang area, Gyeongsangnamdo. The wall rock alteration and genesis of the Milyang pyrophyllite deposit were studied. The ore minerals are composed dominantly of pyrophyllite accompanied by small amounts of quartz, kaolinite, pyrite, dumortierite and diaspore. The alteration halo of this deposit can be divided into three zones on the basis of mineral assemblage; pyrophyllite, sericite and chlorite zone. The common mineral assemblages of each alteration zone are as follows: (1) pyrophyllite zone; pyrophyllite-quartz-kaolinite-pyrite-dumortierite-diaspore, (2) sericite zone; sericite-quartz-pyrite-kaolinite, and (3) chlorite zone; chlorite-plagioclase-quartz. Major element chemistry shows that characteristic depletion in MgO, CaO, and $Na_2O$ and relative increase in FeO from less altered chlorite zone to extensively altered pyrophyllite zone corresponding to variation in mineral assemblages. The paragenesis of ore minerals, oxygen isotope data, chlorite and illite geothermometry suggest that ore deposit was formed at about $250{\sim}330^{\circ}C$. Both hydrogen and silica activities are high in pyrophyllite zone. Potassium activity increases in sericite zone while hydrogen activity becomes low in chlorite zone. The pyrophyllite zone was formed relatively higher temperature than those of sericite and chlorite zones. The ore fluid was considered to be magmatic water in origin derived from the residual granitic magma which interacted with meteoric water.