• 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.

• Journal of the Mineralogical Society of Korea
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• v.7 no.1
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• pp.40-48
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• 1994

The weathering of the Namsan granite was studied in terms of sorption process. The Namsan granite consists mainly of quartz, alkali feldspar, plagioclase (${Ab_{85}An_{15}}-Ab_{100}$ and biotite with small amounts of sericite, magnetite and ilmenite. The kinetic factors for altering the granite body are the proton and hydroxyl ions derived from the reaction of water and mineral. There are two different types of pH variation curves for rocks of different mineral assemblages. when powdered granite was dispersed in distilled water under ambient condition. The sorption-process proceeds by three steps for fresh granite; (1) the initial rapid pH-rise to 10 by the uptake of proton by negatively charged mineral surfaces, (2) the gradual pH-down, and (3) the stable pH tail between 7.1-7.5. For somewhat weathered granites, the sorption proceeds; (1) the initial rapid pH-down to 4.8, (2) the slight pH-rise and slow ph-down, and (3) the stable pH tail between 5.0-5.3. The reaction rate is controlled by the density of adsorbable sites, the solubility of the mineral, pH of the system and formation of amorphous gel and gibbsite. Amorphous gel floates on the surface of the solution while stirring the powdered granite and then is transformed into gibbsite in an hour or so. The pH saturation values for -325 mesh fresh granite from 5 m depth is about pH 10 when rock/water ratio is over 10g/200 ml.

• Journal of the Korean earth science society
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• v.21 no.5
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• pp.553-562
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• 2000

Daejeonsa basalt in the Mt. Juwang area is composed of 12 lava flows alternate with 9 peperites, and each lava and peperite has variable thickness. Globular peperites yielded in Daejeonsa basalt are mixed basalt clasts with reddish shale. Based on field description, when lava flows over unconsolidated wet shale or injectes into unconsolidated wet shale, peperites were formed at the contacts between lava and shale. Daejeonsa basalt are massive lava flows with rare vesicules: some vesicules are found in upper part of a flow unit. The basalt has mainly pseudomorphs of olivine as phenocryst, and also plagioclase and clinopyroxene phenocrysts in rocks with higher Mg-number. Matrix is mainly subophitic texture, sometimes showing ophitic and intergranular textures due to different cooling rate. Clinopyroxene is augite(Wo$_{41.6}$En$_{45.1}$Fs$_{13.3}$), and plagioclase is mostly labradorite(An$_{55.0}{\sim}_{67.7}$), but some is andesine(An$_{44.3}$) and bytownite(An$_{74.5}$). Oxide minerals are composed of titanomagnetite and ilmenite.

• 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.5 no.1
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• pp.52-65
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• 1996

Precambrian metamorphic rocks of the Cheongpyeong-Yangpyeong area, central Gyeonggi massif, comprise gneiss, schist, quartzite and amphibolite. Mineral, assemblages of pelitic gneisses are characterized by biotite + cordierite + garnet + sillimanite + K-feldspar + plagioclase + quartz together with minor muscovite, spinel and corundum, and represent the granulite facies metamorphism. In particular, kyanite occurs as fine-grained relict phase inside plagioclase of three gneiss samples. Metamorphic conditions are estimated from garnet-biotite and garnet-cordierite geothermometers in conjunction with garnet-$Al_2SiO_5$-quartz-plagioclase (GASP) and garnet-rutile-$Al_2SiO_5$-ilmenite (GRAIL) geobarometers. They are 700-$850^{\circ}C$ and 3.2-8.3 kbar, and 580-$690^{\circ}C$ and 2.1-3.2 kbar, respectively, when the core and rim compositions of garnet are use. Garnet of the GASP assemblage increases rimward in the Fe and Mn contents but decreases in the Mg content, whereas its Ca content does not vary significantly. Together with the occurrence of relict kyanite and the result of P-T estimates, compositional zoning patterns of garnet indicate a clockwise P-T history. Moreover, the preservation of high-pressure minerals such as kyanite in plagiocalse, even after the medium-pressure granulite facies metamorphis, suggests a rapid change in P-T conditions.

• Journal of the Mineralogical Society of Korea
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• v.31 no.2
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• pp.87-101
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• 2018

The Manjang deposit developed in the Hwajeonri formation of the Okcheon metamorphic belt consists of the Central and Main orebodies of Cu-bearing hydrothermal vein type and the Western orebody of Fe-skarn type. This study focuses on the Cu mineralization of the Central and Main orebodies to compare with the genetic environments of the Western orebody previously studied. The Central orebody produced pyrrhotite and chalcopyrite as major ore minerals with vein texture, while the Main orebody contains pyrite, arsenopyrite, and chalcopyrite as major ore minerals with vein, massive, and brecciated texture. Sphalerite, galena, magnetite, ilmenite, rutile, cassiterite, wolframite, and stannite are also accompanied. Local occurrence of skarn is dominated by grossular and hedenbergite, reflecting the reduced condition of the skarnization. Geothermometries of sphalerite-stannite in the Central orebody and arsenopyrite-pyrite in the Main orebody indicate the formation temperature of $204-263^{\circ}C$ and $383-415^{\circ}C$, respectively. Sulfur fugacity of $10^{-6}-10^{-7}atm$. in the Main orebody decreased toward the Central orebody. Sulfur isotope compositions of sulfide minerals from the Central and Main orebodies are 4.6-7.9‰ and 4.3-7.0‰, respectively, reflecting magmatic origin with slight influence by host rock. Considering ore mineralogy, texture as well as physicochemical conditions, the Main and Central orebodies of hydrothermal Cu mineralization reflect the characteristics of proximal and distal type ore mineralization, respectively, related to hidden igneous rocks, and they were generated under different hydrothermal systems from the Fe-skarn Western orebody.

• The Journal of the Petrological Society of Korea
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• v.14 no.4 s.42
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• pp.212-225
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• 2005

This study has been designed to elucidate the morphology of Jisagae columnar joints and the petrography and petrochemistry of Daepodong basalt in Jeju Island, distributed along the 3.5 km-long coast from Seongcheonpo to Weolpyeongdong. Colonnade of the Jisagae columnar joint typically occurs within the upper part of a flow and consists of relatively well-formed basalt columns. Most columns are straight with parallel sides and diameters from 100 cm to 205 cm, $130\~139\;cm$ in maximum. Length of the columns extends up to 20 m. Most columns tend to have 6 or 5 sides but sometimes they have as few as $3\~4$ or as many as 7 or 8 sides. The Daepodong basalt consists of plagioclase, olivine, orthopyroxene, clinopyroxene, ilmenite and magnetite. Plagioclase is labradorite, clinopyroxene is augite, orthopyroxene is bronzite and olivine is chrysolite and hyalosiderite. The Daepodong basalt shows porphyritic texture with matrix of mainly intersetal texture. The Daepodong basalt is plotted into alkali rock series on the TAS diagram. The tectonic setting of the Daepodong basalt represents within plate environment.

• The Journal of the Petrological Society of Korea
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• v.12 no.1
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• pp.1-15
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• 2003

The Paekrogdam summit crater area, Mt. Halla, Jeju Island, Korea, composed of Paekrogdam trachyte, Paekrogdam trachybasalt, and Manseidongsan conglomerate in ascending order. Joint systems show concentric and radial patterns around the summit crate wall. The Paekrogdam crater is a summit crater lake which erupted the tuffs, scorias and lava flows of Paekrogdam trachybasalt after the emplaceent of Paekrogdam trachyte dome. SiO$_2$ contents of mafic and felsic lavas are respectively, 48.0∼53.7 wt.％ and 60.7∼67.4 wt.%, reflecting bimodal volcanism. And lavas with SiO$_2$ between 53.7 wt.% and 60.7 wt.％ are not found. According to TAS diagram and K$_2$O-Na$_2$O diagram, the volcanic rocks belong to the normal alkaline rock series of alkali basalt-trachybasalt-basaltic trachyandesite and trachyte association. Oxide vs. MgO diagrams represent that the mafic lavas fractionated with crystallization of olivine, clinopyroxene, magnetite and ilmenite and felsic trachyte of plagioclase and apatite. The characteristics of trace elements and REEs shows that primary magma for the trachybasalt magma would have been derived from partial melting of garnet peridotite mantle. In the discrimination diagrams, the volcanic rocks are plotted at the region of within plate basalt (WPB).

• The Journal of the Petrological Society of Korea
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• v.4 no.1
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• pp.1-19
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• 1995

In order to characterize the petrogenesis of the E-W trending Imjinganag belt, we studied the metamorphic rocks of the Yeoncheon Group near its type locality, Yeoncheon - Cheongok area, belonging to the southern part of this fold-thrust belt. The Samgot Formation of the Yeoncheon Group consists of calc-silicate and metapsammitic rocks together with amphibolite and amphibole gneiss. Layers of these metamorphic rocks concordantly occur in a wide area with its length greater than 15 km along their strike direction. Major mineral assemblages of the amphibolite are hornblende + plagioclase ${\pm}$ garnet ${\pm}$ diopside ${\pm}$ biotite ${\pm}$ quartz. Accessory rutile and ilmenite are characteristically replaced by titanite. Metamorphic temperatures and pressures estimated from the garnet - hornblende - plagioclase - quartz geothermo-barometers are 632-$736^{\circ}C$ and 7.9-11.1 kbar, respectively. Thus, the regional metamorphism of the study area belongs to the upper amphibolite facies. Furthermore, Sm-Nd and Rb-Sr data of garnet, plagioclase, and whole rock of an amphibolite define mineral isochrons of $231{\pm}30$ Ma and $222{\pm}24$ Ma, respectively, suggesting the Triassic metamorphism. These results are consistent with P-T conditions and metamorphic ages reported in the Shandong Peninsula, and support the hypothesis that the Chinese collision belt may extend into the Imjingang belt in the Korean Peninsula.

• Economic and Environmental Geology
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• v.37 no.2
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• pp.153-171
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• 2004

This study was carried out to define the geochemical and mineralogical relationship between stream sediments and regional geology on upstream of Hahn river area. Geochemical characteristic including for major elements, trace elements and rare earth elements of the South and North Hahn river bed sediments are similar to those of acid igneous rocks which are distributed around both Hahn river basin. The chemical variation of major elements against SiO$_2$ and trace elements contents between South and North Hahn river bed sediments doesn't show the difference. REE patterns of both area show a distinct negative Eu anomaly, but total contents of rare earth elements are higher in North Hahn river sediments than South Hahn river sediments. The heavy minerals in the river bed sediments in this study area are identified as tremolite-actinolite, hematiteㆍmagnetite, common hornblende, ilmenite, garnet, epidote, rutile and sphene. In conclusion, it is elucidated that South and North Hahn river bed sediments are being originated from igneous rocks or metamorphic rocks which contains medium-high grade metamorphic minerals and components of originated from sedimentary rocks those of politic or calcareous rocks are eroded away as solution or suspended load.