• Economic and Environmental Geology
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• v.21 no.1
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• pp.69-83
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• 1988

Orthogneiss of the study area is meta-igneous complex that composed of granite gneiss, porphyroblastic gneiss and migmatitic gneiss. Migmatitic gneiss produced from granite gneiss and porphyroblastic gneiss by strong ductile shearing. These rocks show mostly gneissic and partly mortar textures by strong regional metamorphism and ductile shearing during several orogenies. $^{40}Ar-^{39}Ar$ incremental-release ages of these rocks have been determined for 1 hornblende. 1 biotite and 3 muscovite concentrates separated from orthogneisses in this area. Ages of regional metamorphism and ductile shearing of these rocks are more than 5 stages(1500 Ma, 260 Ma, 190 Ma, 180-170 Ma and 160 Ma) under $300^{\circ}C$ to $500^{\circ}C$. These rocks had not been nearly effected by Daebo orogeny, because this area is far from Daebo granite bodies. The general trend of major chemical composition and mineral composition of these orthogneisses suggest that these rocks are some series of differentiated products from magma.

• Economic and Environmental Geology
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• v.20 no.4
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• pp.235-246
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• 1987

Busan migmatitic gneisses in the northeastern margin of the Ogcheon zone have been studied petrologically in order to clarify their origin. Petrochemical and mineralogical studies show that the gneisses are Precambrian basemental paragneisses and the rocks were migmatized more intensively than the Bagdalryeong gneisses which have been known to constitute the basemental gneisses of Ogcheon zone. K-Ar biotite isotopic ages are $150.79{\pm}3.37Ma$ in Busan migmatitic gneiss and $191{\pm}4.27Ma$ in Bagdalryeong gneisses. These ages seem to be isotopic homogenised ages. Progressive regional metamorphisms are predominent in the studied area showing greenschist facies, epidote amphibolite facies and amphibolite facies toward N-W direction.

• Proceedings of the Petrological Society of Korea Conference
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• 2006.02a
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• pp.43-60
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• 2006

The Yeongnam Massif, one of Precambrian basements in Korean Peninsula, is characterized by widespread occurrence of low-pressure/high-temperature (LP/HT) schists and gneisses accompanying extensive anatexis and granitic magmatism. Metapelitic mineral assemblages define three progressive metamorphic zones pertinent to low-pressure facies series: cordierite, sillimanite and garnet zones with increasing temperature. Metamorphic grade ranges from lower amphibolite to lower granulite facies and metamorphic conditions reach ca. 750-800 C and 4-6 kbar in migmatitic gneisses. Migmatitic gneisses are prominent in the sillimanite and garnet zones. Textural and petrogenetic relationshipsin leucosome suggest that migmatitic gneiss is the product of anatexis of metasedimentary rocks. The migmatite formation during the prograde metamorphism is governed initially by fluid-present melting and subsequently by biotite-dehydration melting. The large amount of leucosomes in the sillimaniteand garnet zones can be explained by the fluid-present molting possibly triggered by an external supply of aqueous fluid. Field and geochronologic relationships between leucogranites and migmatitic gneisses further suggest that leucogranite has providedfluid and heat required for widespread migmatization.

• The Journal of the Petrological Society of Korea
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• v.4 no.1
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• pp.61-87
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• 1995

On the basis of lithology, the Precambrian Hongjesa Granitic Gneiss can be locally zoned into granoblastic granitic gneiss, porphyroblastic granitic gneiss, migmatitic gneiss from its center to the marginal part. There are no distinct differences in mineral assemblages by lithologic zoning, but it partly shows the change of mineral assemblage in the adjacent with migmatitic gneiss, thus mineral assemblage can be subdivided into Zone I and Zone II. In terms of mineral compositions, the characteristics of Zone I are coexisting K-feldspar+muscovite+sillimanite. The characteristics of Zone II are (1) breakdown of muscovite, (2) coexisting garnetScordierite, (3) coexisting garnet+cordierite + orthoamphibole. The Buncheon Granitic Gneiss is mainly composed of augen gneiss. In the adjacent area with Honjesa Granitic Gneisses, Buncheon Granitic Gneiss has the mineral assemblage of sillimanite+biotite+K-feldspar+(kyanite). Kyanite occurs as relict grains in the Buncheon and Hongjesa Granitic Gneissess. Kyanite shows anhedral to subhedral form and coexists with sillimanite in only one of these samples. Garnet from a migmatitic gneiss (Zone 11) has relatively high $X_{Fe}$ value in core and rim. Garnet from a porphyroblastic granitic gneiss(Zone I) has relatively homogemeous core but compositionally-zoned rim. Biotites show various colour from greenish-brown, brown to reddish brown at maximum adsorption. Also, the Ti, and Mg content in biotites increases from Zone I to Zone II. The plagioclases shows the chemical composition of $Ab_{84}An_{16}$ -$Ab_{70}An_{30}$ (oligoclase) in Zone I and $Ab_{70}An_{30}$ -$Ab_{50}An_{50}$(andesine) in Zone 11. These variations indicate that the gneisses in the study area experienced a upperamphibolite facies. The presence of kyanite as relict grains indicates that the metamorphic rocks in this area exprienced a high-temperature/medium-pressure type metamorphism, followed by high-temperaturellow-pressure metamorphism. Metamorphic P-T conditions for each gneiss estimated from various geothermobarometers and phase equilibria are 698-$729^{\circ}C$/6.3-11.3 kbar in augen gneiss, 621-$667^{\circ}C$/1.0-5.4 kbar in migmatitic gneiss, and 602-$624^{\circ}C$/1.9-3.4 kbar in porphyroblastic granitic gneiss. These data suggest that the study area was subjected to a clockwise P-T path with isothermal decompression (dP/dT=about 60 bar/$^{\circ}C$).

• The Journal of the Petrological Society of Korea
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• v.8 no.3
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• pp.183-202
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• 1999

The Sobeaksan Gneiss Complex in the Punggi area is composed of mainly mignatitic gneiss, porphyroblastic gneiss, garnet granitic gneiss and biotitie granitic gneiss. Metamorphic grade increase gradually from the amphibolite facies of northwestern part to the granulite facies of southwestern part in the study area. Representative mineral assemblage in the amphibolite facies is biotite-muscovite-K-feldspar-plagioclase$\pm$garnet$\pm$epidote, needle shape or fibrous sillimanite occur in transitional zone from the amphibolite facies to the granulite facies. In the granulite facies, the garnet-Opx granulite shows garnet-orthopyroxene-biotite-plagioclase, the metabasite shows clinopyroxene-plagioclase$\pm$hornblende$\pm$orthopyroxene$\pm$garnet and the migmatitic gneiss shows garnet-biotite-sillimanite-cordierite$\pm$spinel as representative mineral assemblage. Retrograde metamorphism after the granulite facies metamorphism made corindum and andalusite in the migmatitic gneiss and the thin layer garnet between clinopyroxene and plagioclase in the metabasites. The peak P-T conditions of the migmatitic gneiss and the garnet-Opx granulite are $916^{\circ}C$/6.6 kb and $826^{\circ}C$/6.3 kb, respectively. The P-T condition of biotite and plagioclase inclusion, which indicates the progressive condition of the granulie facies, within garnet is $866^{\circ}C$/7.5 kb and that of rim composition of garnet and biotite is $726^{\circ}C$/4.6 kb, which infer the clockwise P-T path of the granulite facies metamorphism. The temperatures caculated by the rim composition of garnet and biotite in the migmatitic gneiss and garnet granitic gneiss have a wide range of $556-741^{\circ}C$, which indicate that the retrograde metamorphism after the granulite facies metamorphism has effected differently. It is difficult to determine the P-T condition of the biotite granitic gneiss because less occurrence and higher spessartine content of garnet. The P-T condition of the thin layered garnet between clinopytoxene and plagioclase in the metabasite is $635-707^{\circ}C$/4.1-5.3 kb. This texture indicates the isobaric cooling(IBC) condition of the retrogressive metamorphism. As a result, the metamorphic evolution of the Punggi area has undergone the isobaric cooling after the granulite facies metamorphism which has undergone the clockwise P-T path.

• The Journal of the Petrological Society of Korea
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• v.1 no.1
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• pp.34-41
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• 1992

The Precambrian granitic gneisses are widely distributed in the Danyang-Yecheon area, eastern part of Korea, where the Ryeongnam massif borders the Ogcheon fold belt. They are composed of migmatitic, biotite granitic, garnet-bearing and granoblastic granitic gneisses. The common joint sets of the granitic gneiss are NE and NS directions, which are probably related to the effects of Daebo orogeny and Bulgugsa disturbance, respectively. Mineral assemblages of the banded gneiss xenolith in the garnet-bearing granitic gneiss are quartz-plagioc1ase-biotite-mus-covite-orthoclase and quartz-plagioc1ase-biotite-garnet, belonging to the amphibolite facies. The granoblastic granitic gneiss is felsic, metaluminous, and granitic, and shows subalkaline trend. The garnet-biotite geothermometry of garnet-bearing granitic gneiss yields 640$^{\circ}$-708$^{\circ}C$ at pressure of 4 kb.

• The Journal of the Petrological Society of Korea
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• v.7 no.2
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• pp.111-131
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• 1998

The migmatitic gneiss in the Odesan Gneiss Complex has small amount of quartzite, amphibolite and marble and the Kuryong Group which contact with migmatitic gneiss unconformitly, also contains some amphibolite. Preview studies of this area had regarded that the amphibolites contact with marble had been produced by metasomatism from the pelitic and calcareous sediments mixtures, but the amphibolite is reinterpreted as igneous origin. $SiO_2$ content of the amphibolite is 45.9~52.7 wt%, which corresponds to basaltic composition. MgO content has narrow range (4.6~6.87 wt%) and major and trace element are plotted against MgO,$TiO_2, P_2O_5$, Hf, Zr are reduced and Cr and Ni are increased their content with increasing MgO. This phenomenon indicates that the basaltic magma as the protolith of the amphibolite had frationated with the crystallization of the pyroxene and/or olivine. REE pattern has smoothly decrease from LREE to HREE. Eu/Eu(0.83~1.19) show the flat Eu anomaly, which indicate small fractional crystallization of plagioclase. HREE is enriched in the garnet-bearing amphibolites. Several discrimination diagram for the basaltic magma show that the amphibolite of the study area is originated tholeiitic basaltic magma indicating continental rift environment. Due to determine the metamorphic condition garnet-hornblende geothermometry and hornblende-plagioclase geobarometry are used. Peak metamorphic temperature range of the amphibolite $788~870^{\circ}C$ and is deduced toward the northeastern part. The calculated temperature from the amphibolite has slightly higher than the temperature of the metapelites but the trend of metamorphic grade which decrease from western to eastern part progradly is similar to each other. The metamorphic pressure calculated by garnet- hornblede-plagioclase geobarometry is 4~5kb. But ilmenite-plagioclase pair enclosed in garnet show 8 kb at $700^{\circ}C$ by garnet-ilmenite-rutile-plagioclase geobarometery. The zonal profile of garnet in sample 84 shows the bell-shape profile, which grossular content decreases whereas pyrope content increases progressively. This means that the amphibolite has undergone the clockwise P-T-t path which is shown in the migmatitic gneiss of the Odesan Gneiss Complex.

• Economic and Environmental Geology
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• v.36 no.4
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• pp.275-284
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• 2003

We collected the samples of stream sediments from primary channels in order to establish natural background of major and minor elements for geologic units in the Gurye area. Stream sediments samples having no possibility of contamination effect and representing drainage basins composed of uniform geology, were collected from April to May in 1999, the chemical analysis of which was carried out. The tolerable level was used to investigate the enrichment degree of harmful elements. The contents of Ni and Cr exceeded the tolerance level in some sections. The tolerance level excess of those elements was regarded as the effect of the metamorphic rock which constituted the bed rock of the area. In order to identify the comprehensive enrichment pattern, the tolerable level was used in calculating the enrichment index. The enrichment index of harmful heavy metals showed that Granite gneiss area is 0.39, Porphyroblastic granite gneiss area 0.32, Biotite gneiss area 0.42, Migmatitic gneiss area 0.41, Tuff area 0.30, Andesite area 0.46, Conglomerate area 0.42, and Granite area 0.26. Those results showed that natural background of Gurye area had not been exposed to harmful heavy metal elements.

• Korean Journal of Mineralogy and Petrology
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• v.33 no.4
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• pp.339-347
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• 2020

We carried out the U-Pb age dating of zircon from basement rocks in the southern part of the Danyang National Geopark. Two migmatitic gneisses composed of biotite±sillimanite±garnet+feldspar+quartz were dated. Leucosomes in the samples were clearly distinguished from their melanosomes. The U-Pb isotopic compositions of zircon from sillimanite- and garnet-bearing migmatitic samples were measured using a secondary ion microprobe, yielding metamorphic ages, 1870±10 Ma (2σ)와 1863±6 Ma (2σ), respectively. 1.87~1.86 Ga metamorphic ages are consistent with those of the Paleoproterozoic low-P and high-T regional metamorphism (1.87~1.85 Ga) in the Yeongnam Massif. The maximum depositional age based upon the apparent 207Pb/206Pb ages of detrital zircon in the samples was estimated as 2.06 Ga, and thus sedimentation age of the protolith of the migmatitic gneisses ranges between 2.06 and 1.87 Ga.

• The Journal of the Petrological Society of Korea
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• v.20 no.2
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• pp.99-114
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• 2011

Precambrian gneiss complex in the Pyeongchang-Wonju area, which lies west of the Paleozoic sedimentary basin of the Yeongwol-Taebaek area, is being considered as a part of the Gyeonggi massif, but its ages of formation and metamorphic events are not well defined yet. In this study, SHRIMP zircon U-Pb ages were determined from the gneiss complex in the area, We obtained the discrete ages of magmatic (ca. 1960 Ma) and metamorphic (ca. 1860 Ma) events through the interpretation of the SHRIMP data based on the internal structures of zircons. These are almost the same to the ages of main intrusion and metamorphism reported from the Precambrian basements of Gyeonggi, Yeongnam and Nangnim massifs of the Korean Peninsula, Ages of 3200~3300 Ma, 2900 Ma, 2660 Ma, 2430 Ma, 2260 Ma, and 2080~2070 Ma obtained from inherited cores of studied zircons are also very similar to the frequently reported ages from the basement rocks of the Gyeonggi and Yeongnam massifs, Lower intercept age of about 270 Ma calculated from the rim data seems to indicate that the study area suffered from a late Paleozoic metamorphism (Okcheon Orogeny), but we need more reasonable and sufficient data to confirm it. According to the results of this study, it is suggested that the Bangnim group unconformably overlying the gneiss complex was deposited after the Paleoproterozoic granitic magmatism (ca. 1960 Ma) and metamorphism (ca. 1860 Ma).