• Economic and Environmental Geology
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• v.46 no.5
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• pp.391-409
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• 2013

The Hongseong area of the southwestern Gyeonggi massif is considered to be part of suture zone that is tectonically correlated with the Qinling-Dabie-Sulu belt of China in terms of the preservation of collisional evidences during Triassic in age. The Wolhyeonri complex, preserved at the center of the Hongseong area, consists mainly of Neoproterozoic orthogneisses and Middle Paleozoic intermediate- to high-grade metamorphic schists, orthogneisses and mafic metavolcanics. The area includes various Middle to Late Triassic intrusives (e.g. dyke or stock). They are mainly monzonite and aplite with small intrusions of monzodiorit, syenite and diorite in composition. The SHRIMP U-Pb zircon ages yield 237 Ma to 222 Ma. The geochemistry of the studied Triassic intrusives show similar subuction- or arc-type signatures having Ta-Nb troughs, depletion of P and Ti, and enrichment of LILEs (large ion lithophile elements). In addition, the Triassic plutons in the Hongseong area, including those from this study, mostly possess high-K calc-alkaline to shoshonitic tectonic affinity. These results could be tectonically correlated to the post-collisional magmatic event following the Triassic collision between the North and South China blocks in China. Therefore, the Triassic plutons in the Hongseong area offer an important insight into the Triassic geodynamic history of the NE Asian region.

• The Journal of the Petrological Society of Korea
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• v.17 no.1
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• pp.36-43
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• 2008

Many plutonic rock fragments of granitic composition were collected from the Deception Island. We obtained K-Ar ages of $62.5{\pm}1.2\;Ma$ and $140.7{\pm}2.7\;Ma$ from the two samples. Such result contradicts the general belief that most of the volcanic rocks of Deception Island are products of very recent activities and their maximum age does not exceed 200 ka. On the other hand, Mesozoic to Cenozoic rocks produced by subduction-related active magmatism have been reported from both South Shetland Islands and Antarctic Peninsula, located to the north and south of the Deception Island respectively. Also, various kinds of plutonic rocks with granitic composition are distributed widely. Therefore, plutonic rock fragments with granitic composition discovered from the Deception Island seem to indicate their derivation by capturing granitic crustal material underlying volcanic edifice during the volcanic activities, instead of differentiation from magmas related with recent volcanism. Ages and rock types of the plutonic rock fragments suggest arc-related origin just as adjacent South Shetland Islands and Antarctic Peninasula.

• The Journal of the Petrological Society of Korea
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• v.27 no.2
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• pp.85-96
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• 2018

The Neoproterozoic Gyemyeongsan Formation and the Mesozoic igneous rocks are distributed in the Eoraesan area, Chungju which is located in the northwestern part of Ogcheon metamorphic zone, Korea, and the rare earth element (REE) mineralized zone has been reported in the Gyemyeongsan Formation. We drew up the detailed geological map by the lithofacies classification, and measured the radioactivity values of the constituent rocks to understand the distribution and characteristics of the source rocks of REE ore body in this paper. It indicates that the Neoproterozoic Gyemyeongsan Formation is mainly composed of metapelitic rock, granitic gneiss, iron-bearing quartzite, metaplutonic acidic rock (banded type, fine-grained type, basic-bearing type, coarse-grained type), metavolcanic acidic rock, and the Mesozoic igneous rocks, which intruded it, are divided into pegmatite, biotite granite, gabbro, diorite, basic dyke. The constituent rocks of Gyemyeongsan Formation show a zonal distribution of mainly ENE trend, and the distribution of basic-bearing type of metaplutonic acidic rock (MPAR-B) is very similar to that of the previous researcher's REE ore body. The Mesozoic biotite granite is regionally distributed unlike the result of previous research. The radioactive value of MPAR-B, which has a range of 852~1217 cps (average 1039 cps), shows a maximum value among the constituent rocks. The maximum-density distribution of radioactive value also agrees with the distribution of MPAR-B. It suggests that the MPAR-B could be a source rock of the REE ore body.

• Proceedings of the Mineralogical Society of Korea Conference
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• 2002.05a
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• pp.37-39
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• 2002

• Geotechnical Engineering
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• v.35 no.5
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• pp.39-43
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• 2019

• The Journal of the Petrological Society of Korea
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• v.13 no.1
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• pp.1-15
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• 2004

In this study we propose that the ‘enclaves’ which occur in the granites should be translated into ‘Po-yu-am’in Korean. Also we suggest some criteria to discriminate the mafic microgranular enclaves (MME) of igneous origin from the xenoliths, which possibly come from the plutonic, volcanic and sedimentary country rocks. The color of the MME is gray green∼dark gray and the mineral grains are fine and equigranular. The MME are generally of ellipsoidal shape and can be easily found within the granites. They do not show any evidence of contact metamorphism by granite host. On the other hand. the xenoliths are generally of angular shape and are of the same mineral assemblage and texture as the country rocks around the granites. The distribution of the xenoliths is mostly concentrated along the intruding plane of the granites near the country rocks. The xenoliths were partly metamorphosed by the granite intrusion. The xenoliths from the plutonic rocks are easily distinguished from the MME in terms of their angular shape and coarser grain size, but they do not have any metamorphic mineral assemblage and texture. The xenoliths from the tuffaceous rocks show angular shape and porphyritic and pyroclastic textures. Large size xenoliths from the sedimentary rocks specifically preserve bedding structure which are indicative of the sedimentary strata. However, the sedimentary xenoliths of small size are often difficult to distinguish from the MME. Metamorphic minerals and texture are a useful key to discriminate the small-sized sedimentary xenoliths from the MME. In summary the xenoliths in the granites can be megascopic ally distinguished from the MME by comparing their color, shape, grain size and remnant original structure like bedding. Additionally the metamorphic mineral assemblage and texture are microscopic discriminators between the xenoliths and the MME in the granites.

• Journal of the Korean earth science society
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• v.27 no.5
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• pp.528-538
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• 2006

Main aspect of this study is to clarify the petrochemistry and petrogenesis of intermediated-basic plutons located in the southwestern part of the Korean peninsula. These Intermediated-basic plutons consist of Pre-Cambrian anorthosite-gabbro, Triassic hornblende gabbro (Jirisan area), Jurassic diorite-syente (Jirisan and north area) and Cretaceous gabbro-diorite (south area). The Massif type anorthosite has multi intrusions, where each one intruded by gabbroic rocks, composed of gabbro, norite, troctolite and leucogabbro. In the variation diagram of the major-minor composition, AMF and Pl-Px-Ol diagrams, we suggest that intermediated-basic plutons in the southwestern part of the Korea show a trend consistent to Daly's value and calc-alkaline rock series. Accoding to REE (La/Yb)cw and Eu/Sm, these plutons are enriched with LREE than HREE, and emplaced by the tectonic setting in continent and/or continental margin.

• The Journal of the Petrological Society of Korea
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• v.13 no.2
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• pp.47-63
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• 2004

This study focuses on the petrography and petrochemical characteristics of the volcanic and plutonic rocks in Gadeog island, Busan, Korea. Based on textural and mineralogical characteristics, intermediate volcanic rocks can be divided into andesitic lava flows (porphyritic and massive andesites) and andesitic pyroclastics. Felsic volcanic rocks are composed of rhyolite, rhyolitic welded tuff, and tuff breccia. Plutonic rocks are intruded rhyolite and andesitic rocks, and composed of hornblende granodiorite which contains lots of mafic magma enclaves. Volcanic rocks are composed of andesite, dacite and rhyolite having a range in SiO$_2$ from 59 to 78wt.%. The volcanic rocks belong to the calc-alkaline rock series. Plutonic rocks have a range in SiO$_2$ from 63 to 69wt.%. This compositional variations correspond to those of Cretaceous volcanic and plutonic rocks in the southeastern Gyeongsang basin. The trace element composition and rare earth element patterns of the volcanics, which are characterized by high LREE/HFSE ratios and enrichment in LREE, suggest that they are typical of calc-alkaline volcanic rocks produced in the subduction environment around continental arc. We concluded that volcanic and plutonic rocks in Gadeog Island were evolved from orogenic andesitic magma which was produced by partial melting of the mantle wedge in the subduction environment.

• Economic and Environmental Geology
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• v.37 no.5
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• pp.555-568
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• 2004

The demand of aggregate resources in Korea has been increased with a rapid economic growth since the 1980s. About 25% of the total aggregate production is derived from riverine aggregates, 20% to 25% from marine sands, 40% to 45% from crushed aggregate and the rest 5% to 15% from old fluvial deposits. The abundance of crushed coarse aggregates varies in the uniform distribution of country, but in general it can be concentrated in the most densely populated areas, five main cities. Typical rock types of the Korean crushed stones are classified as plutonic rocks of 27%, metamorphic rocks of 32%, sedimentary rocks and volcanic rocks of 18%, respectively. The most abundant coarse aggregate used in the country is obtained from granite (25% of total) and subordinately gneiss (20%), sandstone (10%) and andesite (10%). Although rock types using as dimension stone are only fifteen, those as aggregate amount up to twenty nine rocks. These rocks consist of plutonic rocks such as granite, syenite, diorite, aplite, porphyry, felsite. dike and volcanic rocks such as rhyolite, andesite, trachyte, basalt, tuff, volcanic breccia and metamorphic rocks such as gneiss, schist, phyllite, slate, meld-sandstone, quartzite, hornfels, calc-silicate rock, amphibolite. And sandstone, shale, mudstone, conglomerate, limestone, breccia, chert are main aggregate sources in tile sedimentary rocks. The abundance of plutonic rocks is the highest in Chungcheongbuk-do, and decreases as the order of Jeollabuk-do, Gangwon-do and Gyeonggi-do. In Jeollanam-do, volcanic aggregates occupy above 50%, on the contrary sedimentary aggregates are above 50% in Gyeongsangnam-do.

• The Journal of the Petrological Society of Korea
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• v.15 no.1 s.43
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• pp.1-9
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• 2006

Sr isotopic compositions are determined from the syenite of Sancheong area, yielding age of $211{\pm}23(2\sigma)$ Ma and $^{87}Sr/^{86}Sr$ initial ratio of $0.70598{\pm}0.00060$. Such result confirms that Sancheong syenite was emplaced during the Mesozoic around the Triassic-Jurassic boundary. Rather low initial $^{87}Sr/^{86}Sr$ ratio suggests insignificant influence of old crustal materials. There are strong contrast in rock types of plutonic associations between Sancheong-Macheon area and adjacent Hamyang-Geochang area to the north, i.e. syenite-diorite-gabbro and granite-granodiorite respectively. $^{87}Sr/^{86}Sr$ initial ratios also show distinction between these areas. Such differences suggest regional contrast in tectonic environments between them.