• 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.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.

• 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.8 no.1
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• pp.34-45
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• 1999

Mafic granulite xenoliths are found in precambrian porphyroblastic gneiss of the Mt. Jiri area, SW Sobaegsan massif, Korea. The xenoliths are rounded to ellipsoidal in shape, 50-100 cm in length and coarse-grained with granoblastic and foliated texture. The xenoliths consist of orthopyroxene, garnet, biotite, plagioclase, quartz, ilmenite and secondary orthoamphibole. Orthopyroxene is mostly resorbed and rimmed by coronitic orthoamphiboles. Garnets occur as porphyblasts and are zoned with higher pyrope content in cores than in rims. Geothermo-barometry results yield conditions of about $800-850^{\circ}C$, 6 kb and $500^{\circ}C$, 4 kb for early and retrograde stages of equilibration, respectively. According to available geochronological data, it is suggested that the granulite facies metamorphism occurred prior to 2.1-1.9Ga and that the area was superimposed by the high-grade (over $600-700^{\circ}C$) metamorphism between 1.9-1.7Ga, followed by cooling during uplift.

• Journal of the Korean earth science society
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• v.25 no.4
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• pp.251-264
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• 2004

The Charnockite in Sancheong region is quarzofeldspathic rock containing orthopyroxene and garnet with a color dark than common granitic rocks. The Chamockite are mostly massive and medium to coarse-grained with K-feldspar phenocryst, but reveal weak foliation. The rock consist mainly of quartz, K-feldspar, plagioclase and orhopyroxene, with biotite, garnet, and anthophyllite. In petrochemistry, the Chamockite has 61-65% $SiO_2$ contents, varying gradually into the margin contacted with orthogneiss, which have compositions of felsic igneous rocks. Major element show almost systematical variation with those of the marginal orthogneisses, except the hornblende gneiss and anorthosite. The Charnockite and orthogneisses show the tholeiitic differentiational trend. Trace and rare earth element abundance patterns in the Charnockite show remarkable negative Sr and Eu anomalies similar to orthogneisses, but different from the hornblende gneiss and anorthosite. Eu contents of the Charnockite are richer than that of orthogneisses. The metamorphic condition of the Charnockite were tested by an orthopyroxene-garnet geotherrnorneter and a plagioclase-garnet geobarometer. Estimated P-T conditions are about $761^{\circ}C$ and 7 kbar at peak metamorphism, but $653^{\circ}C$ and 6.4 kbar at retrograde metamorphism. This suggests that the Charnockite have from an early stage of high-grade metamorphism to represent the granulite facies and then to a late stage medium-grade metamorphism belonging to the amphibolite facies.

• Journal of the Mineralogical Society of Korea
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• v.28 no.3
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• pp.221-231
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• 2015

Precambrian Jirisan gneiss complex suffered retrograde metamorphism ranging from granulite facies to the amphibolite facies and/or greenschist facies. Intrusive anorthositic rocks in gneiss complex are influenced by late metamorphism. Mafic mineral in anorthositic rock composed mainly of amphiboles, which can anticipate the information about metamorphic conditions and metamorphic facies. Amphiboles from anorthositic rock show subhedral to anhedral in shape and mostly blueish green and/or green in colour in plane polarized light. Some of brownish amphiboles show zonal texture with brownish to blueish green in color from core to rim. Reaction parts in clinopyroxene which exchange with amphibole. It suggests retrograde metamorphism and/or alteration. Amphiboles composing anorthositic rocks can be classified into two types depending on the size and occurrence of amphibole. The first type is microcrystalline amphibole occurring matrix [Group I: ferrohornblende]. The second type is amphibole with 1 mm or larger in size, which is usually occurred in the boundary between opaque mineral and plagioclase [Group II: ferropargasite]. Electron microscopic analyses base on the $Al^{vi}$ composition in amphiboles suggest that the metamorphic pressure of anorthositic rock was low with 5 kbar or less. Ti compositional range in amphibole and representing hornblende+ plagioclase+garnet+biotite+chlorite mineral assemblage suggest that metamorphic facies of anorthositic rock is in amphibolite facies.

• Journal of the Korean earth science society
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• v.26 no.3
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• pp.297-304
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• 2005

Serpentinites in Chungnam area are mainly composed of serpentines. Serpentines of olivine origin consist of pseudomorphs of olivines and show mesh textureen closed with magnetites along the boundaries of serpentine crystals. In some serpentinites, serpentinization is occurred in crystal boundaries and/or cracks of olivines and pyroxenes which are relict minerals of dunite and harzburgite. On the process from olivine to serpentine, Mg ions are greatly decreased and Si ions are greatly increased, and $Fe^{2+}\;and\;Fe^{3+}$ ions are a little decreased. But, on the process from pyroxene to serpentine, Si ions are greatly decreased and Mg ions are greatly increased. Magnetites around the serpentine crystals were formed from the iron which had been left out through this serpentinization process of olivine. Serpentinization from the original rocks such as dunite and harzburgite in Chungnam area was occurred by various waters affected after formation of original rock, and particularly by metamorphic water in the metamorphic conditions ranging from green schist facies to granulite facies through amphibolite facies.

• 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.11 no.3_4
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• pp.103-120
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• 2002

In the Baekdong-Hongseong area, the southwestern part of the Gyeonggi Massif in Korea, ultramafic rocks occur as lenses within Precambrian granitic gneiss. At Baekdong area, ultramafic lens contains metabasite boudin which had undergone at least three stages of metamorphisms. The mineral assemblage on the first stage, Garnet+Sodic Augite+Hornblende+Plagioclase+Titanite, is recognized from the inclusions in garnet. The second stage is represented by the assemblage in matrix, Garnet+ Augite+Hornblende+Plagioclase, while the third stage is identified by the Hornblende+Plagjoclase $\pm$ Garnet assemblage in the symplectite formed around garnet. The P-T conditions of the first and the third stages are $690-780^{\circ}C$, 11.8-15.9 kb and $490-610^{\circ}C$, 4.0-6.3 kb, respectively. These data indicate that metabasite in Baekdong area had experienced a retrouade P-T path from the eclogite(EG) - high-pressure granulite (HG)-amphibolite (AM) transitional facies to the AM through HG-AM transitional facies. The core and rim of garnet in country granitic gneiss give $605-815^{\circ}C$, 10.7-16.0 kb and $575-680^{\circ}C$, 5.4-7.0 kb, respectively, indicating that the retrograde P-T path of granitic gneiss is similar to that of metabasite. Trace element data reveals that the tectonic setting of metabasite is island uc. The general geology, the metamorphic evolution, the mineral chemistry and the tectonic setting of Baekdong area indicate that the Baekdong-Hongseong area in Korea is a possible extension of the Sulu collision Belt in China. On the other hand, the Sm-Nd whole rock-garnet isochron ages of metabasites are 268.7-297.9 Ma which are older than the ages of UHP metamorphism (208-245 Ma) in the Dabie-Sulu Collision Belt. The older metamorphic ages suggest that collision between Sino-Korea and Yangtz plates may have occurred earlier in Korean Peninsula than China.

• The Journal of the Petrological Society of Korea
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• v.9 no.1
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• pp.29-39
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• 2000

For the determination of metamorphic age of the metamorphic rocks distributed in the Ji-san area of Youngnam massif, Sm and Nd isotopic compositions were analyzed for the whole rock and garnet separates. As the result, we obtained 1799 + 11 Ma from the porphyroblastic gneiss, 1776 +30 Ma from the metapelite, 1714+35 Ma from the mafic granulite xenolith within the porphyroblastic gneiss, and 1776+30 Ma from the metapelite occurred as a xenolith within the quartzofeldspathic gneiss. There have been reports of geologic ages similar to such metamorphic ages of Jirisan area from the other portion of the Youngnam massif, which reveals that very intense metamorphism took place over the vast area of Youngnam massif during the period of 1.7-1.8 Ga ago. The granulite facies metomorphism of the Gyeonggi massif also shows the age similar to this period. Such resemblance in their metamorphic ages suggests that these massifs experienced similar tectonothermal events occurred at about the same Precambrian periods, which implies the possibility that the extension of the collision belt between the north and south China blocks does not extend through some places between the Youngnam and Gyeonggi massifs. On the other hand a quarzofeldspathic xenolith of porphyroblastic gneiss show 1928 +42 Ma which is older than above age of the metamorphism and is identical with the zircon U-Pb age of porphyroblastic gneiss indicating the formation age of the protolith of the porphyroblastic gneiss.