• The Journal of the Petrological Society of Korea
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• v.6 no.3
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• pp.226-243
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• 1997

The Odesan Gneiss Complex consists of mainly migmatitic gneiss and porphyroblastic gneiss with locally intercated quartzite, amphibolite, marble and leucocratic gneiss. At least two different regional metamorphisms are recognized in the study area. Metamorphic grade of the first metamorphism increases from the K-feldspar-muscovite zone(in which biotite-muscovite-plagioclase-quartz and garnet-biotite-muscovite-K-feldspar-plagioclase-quartz assemblages occur) in the east and southwestern part of the study area to the K-feldspar-garnet zone(in which garnet-biotite-K-feldspar-plagioclase-quartz, biotite-K-feldspar-plagioclase-quartz, garnet-biotite-K-feldspar-plagioclase-sillimanite-spinel-quartz assemblages occur) in the northwestern part. Kyanite is found as inclusions in plagioclase. The second metamorphism is characterised by occurrence of cordierite. The metamorphic grade of 2nd metamorphism decreases radically from the central-western part near Gaeinsan in which cordierite-garnet-sillimanite-biotite-muscovite-quartz, cordierite-garnet-spinel-sillimanite-biotite-muscovite-quartz assemblages representing the garnet-cordierite zone are observed. The garnet-cordierite zone is surrounded by the sillimanite-cordierite zone which shows cordierite-sillimanite-biotite-plagioclase, cordierite-muscovite-biotite-plagioclase and sillimanite-muscovite-biotite-plagioclase assemblages. The peak metamorphic P-T conditions of the first metamorphism calcuted from garnet-biotite-sillimanite-K-feldspar-plagioclase-spinel assemblage are 5.4~7.4 kb and $776-789^{\circ}C$. Real P-T condition of the first metamorphism might be higher than the calcuated P-T condition according to the study based on the phase equilibria. P-T conditions calcuated from the garnet-biotite in plagioclase are 12.5kb and $650^{\circ}C$ which indicate that the P-T path of the first metamorphism had passed a high pressure condition before the peak metamorphic temperature condition. The peak metamorphic P-T conditions of the second metamorphism calcuated from garnet-biotite-cordierite-spinel-quartz assemblage are $680~750^{\circ}C$ at pressures lower than 6 kb. In the Odesan Gneiss Complex, the first metamorphism of medium pressure and high temperature had occurred after the high pressure condition and fast uplift and then the second metamorphism of low pressure condition occurred after sedimentation of the Kuryong Group.

• The Journal of the Petrological Society of Korea
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• v.4 no.2
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• pp.186-200
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• 1995

구상구조를 보이는무주 구상편마암은 전북 무주군 왕정리일대에 분포하는 정편마암인 함전기석 복운모 화강편마암내에 배태되어 있다. 구상구조는 구상편마암의 기원암인 화강암내에 포획된 이질암이 변성분화작용을 받아 생성된 것으로 사료된다. 구상편마암은 각의 발달이 없는 초생암구로 구성된 TypeI의 암구와 각의 발딜이 있는 TypeII로 구분이 가능하다. TypeII는 단각암구와 다각암구 그리고 핵의 구조에 따라 다양한 형태로 나눌수 이TEk. 구성암은 내핵, 외학, 각, 그리고 기질부로 구성된다. 핵의 장경은 보통 5cm 내지 8cm이며 구형 또는 타원형의 행태로 암구으 중심부를 이루고 있다. 핵의 화학성분은 $Al_2O_3$, total $Fe_2O_3$, MgO, $K_2O$ LREE가 풍부하고 반대로 $Na_2O$, CaO, HREE가 결정된 것이 특징이며, 핵을 주로 구성하는 변성광물은 근청석-규선석-흑운모-올리고클레이스이다. 각은 운모류의 우혹질 각과 장석류의 우백질 각으로 구분되며 수mm내지 수cm의 두께를 이루며 단일각 내지 다각구조를 이루고 있다. 이들은 핵에 비하여 $Na_2O$, CaO가 상대적으로 부화되고 있으며 기질부를 이루는 화강편마암의 조성과 유사하다. 기지루는 반상변정질로 되어 있고 장석 반상변정의 크기는 대략 2내지 3 mm의 크기로 구성되어 있으며 부수적으로 운모류와 소량의 전기석과 규선석이 존재한다. 또한 후기에 유입된 많은 유체들에 의한 후퇴변성작용의 영향으로 장석은 견운모화내지 전기석화되고, 근청석은 피나이트화 되었다.

• The Journal of the Petrological Society of Korea
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• v.7 no.3
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• pp.177-189
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• 1998

Proterozoic gneisss complex of the Paju-Gimpo area, Northwestern Gyeonggi Massif, consists of mainly gneiss and schist with locally intercalated quartzite and metamorphic calcareous rocks. Mineral assemblages of the gneiss and schist are classified into two type: sillimanite free (garnet zone) and sillimanite bearing (sillimanite zone) assemblages. In the Goyang area, Kyanite occurs as metastable relict grain in two gneiss samples, in which sillimanite, garnet, biotite, K-feldspar and plagioclase occur. Cordierite bearing mineral assemblages of gneiss are biotite+garnet+sillimanite+cordierite+plagioclase+quartz ($\pm$K-feldspar, muscovite), and represent the upper amphibolite or granulite facies metamorphism. The metamorphic complex has experienced two different regional metamorphism. The prograde metamorphism is a medium-pressure type characteries by kyanite. The peak metamorphic P-T condition of the prograde metamorphism calculated from the kyanite bearing rock is 7.0~9.4 kb and $718~778^{\circ}C$. The retrograde metamorphism, after the prograde metamorphism, is the low-pressure type characteries by occurrence of cordierite. The peak metamorphic P-T condition of later calculated from the cordierite bearing rock is 3.6~5.5 kb and $750~889^{\circ}C$. Together with the occurrence of relict kyanite, garnet+biotite+plagioclase assemblage as relict in the cordierite, and the result of estimated P-T metamorphic conditions indicate a clockwise P-T path.

• The Journal of the Petrological Society of Korea
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• v.2 no.2
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• pp.74-94
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• 1993

Metabasites and metapelites in the Mungyong area were intruded by Cretaceous granites with radius of 4-8 km. As the distance from granite body increases, the mineral assemblage of metabasite changes from amphibole + plagioclase through amphibole + plagioclase + epidote to amphibole + plagioclase + epidote + chlorite. The compositional variations of amphibole and plagioclase according to the change of metamorphic grade and bulk rock compositions are very complex. Towards the Mungyong Cretaceous granite body, the mineral assemblage of metapelite changes from chlorite+ muscovite(ch1orite zone) through biotite + chlorite + muscovite(biotite zone) to andalusite+biotite + muscovite${\pm}$chlorite or cordierite+ biotite+ muscovite${\pm}$chlorite(cordierite zone). The estimated metamorphic conditions of cordierite zone are 480~$580^{\circ}C$ 1.5-3.3 kb. The theoretical study on the thermal metamorphism caused by the Cretaceous granite with radius longer than 4 km in the Mungyong area suggests the followings: The degree of metamorphism is mainly determined not by the size of granite body but by the temperature of granite intrusion; The country rocks within 2 km from Cretaceous granite have undergone metamorphism with temperature higher than $500^{\circ}C$, which is consistent with the petrological study in the Mungyong area. Mungyong Cretaceous granite caused a low P/T thermal metamorphism to the country rocks; the amphibolite facies metamorphism to the country rocks within 1-2 km from the granite body and the epidote-amphibolite and greenschist facies metamorphism to the country rocks within 2-5 km.

• 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.12 no.2
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• pp.55-65
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• 1999

Spotted cordierite occurs as the result of intrusion of Wolaksan Granite of Cretaceous age in the northern part of the Ogcheon Metamorphic Belt, forming a contact metamorphic zoning in accordance with the distance from the granite body: a cordierite-muscovite-biotite-quartz assemblage and the higher-temperature cordierite-biotite-quartz-(cummingtonite). These quartz-ubiquitous mineral assemblages identified in the cordierite spot seem to reflect Al-deficient condition of the protolith. TEM observations of textural relations between the cordierite and mica within the cordierite spot clearly reflect that cordierite was formed at the expense of micaceous matrix. A structure refinement of the poikiloblastic cordierite was performed by the Rietveld refinement method. Unit cell of the cordierite was determined to be as follows : lower-temperature type: a=17.1480(9)${\AA}$, b=9.7743(6)${\AA}$, c=9.3184(5)${\AA}$, V=1561.9(4)${\AA}$3, higher-temperature type: a=17.136(2)${\AA}$, b=9.751(1)${\AA}$, c=9.322(1)${\AA}$, V=1557.7(4)${\AA}$3. They show a remarkable difference in the unit cell dimension. The refinement results indicate that structural sites of lower-temperature cordierite are wholly occupied by appropriating ions. Compared to this, tetrahedral sites of the higher-temperature type exhibit an order/disorder ranging about 5-8% as the result of substitution between Si4+ and Al3+, except for T26 site occupied wholly by Al3+. These structural differences seem to be related to the formation temperatures of both cordierite types.

• 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.22 no.2
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• pp.117-135
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• 2013

Orbicular granite gneisses occur as a xenolith within two-mica leucogranites, together with early Paleoproterozoic metasedimentary xenoliths, in Wangjeong-ri, Muju area. The whole-rock chemistries and SHRIMP zircon Pb/U ages of the leucogranites indicate that they are S-type granitoids formed in the continental tectonic setting at $1875{\pm}75$ Ma. The SHRIMP age of monazites from the orbicular granite gneiss gives $1867{\pm}4$ Ma as a metamorphic age which is similar to the intrusion age of the two-mica leucogranite within the error range. The similar ages between zircons and monazites represent that the orbicular granite gneisses formed by metamorphism during the intrusion of the two-mica leucogranite; the metasedimetary xenoliths which sank within the parent magma of leucogranites were metamorphosed into orbicular granite gneisses by thermal metamorphism ($650-740^{\circ}C$, 4-6.5 kbar) due to the heat supplied from surrounding magma. During the thermal metamorphism, the core of orbicular granite gneiss mainly consisting of cordierite formed, and in some orbicular granitic gneisses, the leucocratic melt formed by melting of quartz and plagioclase in the core, squeezed out from core and crystallized around the core forming outer rim. The hydrothermal fluid at the late stage of magma differentiation penetrated into the orbicular granite gneisses resulting pinitization of cordierite into chlorite and sericite. As Muju orbicula granite gneiss was formed from sedimentary rocks, it is more appropriate to be called Muju orbicula granitic gneiss.

• The Journal of the Petrological Society of Korea
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• v.3 no.1
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• pp.94-108
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• 1994

The Precambrian granite, and the Yuli group and the Hyeondong gneisss complex are studied to unravel the metamorphic history of the northeastern Sobaeksan massif. The Hongjesa granite, emplaced at 650-$700^{\circ}C$ and $3{\pm}1$ kbar, has been altered at 310-$568^{\circ}C$. Not only the chloritization of biotite but also the sericitization and saussuritization of plagioclase occur at the subsolidus stage. Biotites of the Hongjesa granite vary in their Al, Fe and Mg contents through dioctahedral and tschermakitic substitutions during the subsolidus stage. Secondary muscovites from biotite and feldspars are enriched in their Si and Mg+Fe contents through tschermakitic and trictahedral substitutuions. The metamorphic pressures and temperatures estimated from the Hyeondong gneiss complex are 3.6-6.6 kbar and 593-$718^{\circ}C$, respectively. Local migmatization producing the cordierite-bearing assemblage occurs in the Hyeondong gneiss complex. The Gibbs' method applied to the assemblage of garnet+biotite+plagioclase+quartz in banded gneiss suggests a complex P-T history of the Hyeondong gneiss complex.

• The Journal of the Petrological Society of Korea
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• v.15 no.1 s.43
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• pp.25-38
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• 2006

Metamophic rocks of Samcheog area, northeastern Yeongnam massif, was studied petrochemically. This area includes Precambrian Hosanri Formation (schists and gneisses) and granitoid (Icheon granitic gneiss, leucocratic granite and Hongjesa granite), Cambrian sedimentary rocks, and Cretaceous sedimentary and acidic volcanic rocks. Hosanri formation is composed of quartz+plagioclase+K-feldspar+biotite+muscovite+granet${\pm}$cordierite${\pm}$sillimanite. Mineral assemblage of biotite granitic gneiss, which is massive granodioritic rock with weak foliation, is similar to Hosanri formation. According to mineral assemblages, metamorphic rocks of studied area can be divided into two metamorphic zones (garnet and sillimanite zones). From Icheonri area, major, trace and rare earth element data of biotite granitic gneiss and luecocratic granite suggest that source rock is politic rocks of Hosanri formation and source magma was formed by anatexis and experienced fractionation of plagioclase. Trace element diagram show collisional environment such as syn-collisional, volcanic arc granite. Orientation of faults in study area have three maximum concentrations, $N54^{\circ}\;W/77^{\circ}\;SW,\;N49^{\circ}\;W/81^{\circ}\;NE\;and\;N10^{\circ}\;W/38^{\circ}\;NE$. Structure analysis suggests that faults in study area ware formed by uplift and compression. Faulting age is guessed after Tertiary because some shear joints is developed in dikes to intrusive Cretaceous acidic volcanic rock. Hosanri formation and Icheon granitic gneiss had experienced similar deformation history because they have maximum concentration to foliations, $N89^{\circ}\;E/55^{\circ}\;SE\;and\;N80^{\circ}\;E/45^{\circ}\;SE$, respectively.