• The Journal of the Petrological Society of Korea
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• v.4 no.2
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• pp.144-152
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• 1995

The Jangsan Quartzite of the Joseon Supergroup and the foliated granite (so-called granitlc gneiss of presumed Precambrian age) of the Yeongnam massif are in direct contact at Cheondong-ri area, 6 km @SE of Danyang. sllthough it has been thought traditionally that the Jangsan Quartzite overlies unconformably the f&ted granite, it is difficult to interpret the contact as an unconformity smce the basal conglomerate in- the lower part of the Jangsan Quartzite does not have any clast of the foliated granite, Rather, recent structural studies of this area indlcate that the contact is a ductile shear zone. However, the sense and age of the shear movement are still problematic. Our mesoscopic and microscopic studies of &tre Cheondong-11 semi-brittle shear zone involving foliated cataclasite and phyllonite, which is a pa& of the Ogdong fault, indlcate a top-to-the northeast shearing, i.e., dextral strike slip. We also performed Pb-Pb dating for the age-unknown foliated granite, since the age of deformed granite ccarr emtrain the maximum age of deformation. The whole rock and feldspar Pb isotape data for the foliated granite and a micaceous xenolith define an isoc chron age of $2.16{\pm}0.15$ Ga ($2{\sigma}$;MSWD=4.4) which is interpreted as the emplacement age of the granite. This early Proterozoic age agrees with those of Precambrian igneous activity In the Yeongnam massif reported previously. The obtaiPrfid gge confirms the traditional idea about the age of the foliated granite and indicates that other methd(s) should be employed to constrain the age of the shear movement.

• The Journal of the Petrological Society of Korea
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• v.1 no.1
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• pp.25-33
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• 1992

The southwestern part of Gyeonggi Massif consists mainly of Archean Seosan and Daesan Groups, and Paleoproterozic Bucheon Group with Bucheon and Seosan gneiss complexes which are members of Gyeonggi gneiss complex. In the eastern part of Dangjin fault, Mesoproterozoic Anyang Group and Anyang granite gneiss occur, and in the western part of the fault Taean Group uncomformably overlies Archean and Paleoproterozoic Groups. Metamorphic facies of Archean Groups is mainly upper amphibolite facies which was overprinted by the second amphibolite facies metamorphism and the third greenschist facies metamorphism. Bucheon and Anyang Groups belong to amphibolite and greenschist facies and are partly overprinted by greenschist facies metamorphism which is characteristic for Taean and Daedong Groups.

• Economic and Environmental Geology
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• v.49 no.4
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• pp.315-323
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• 2016

This study reports a gneiss dome in the Hongseong area, southwestern margin of the Gyeonggi massif. This gneiss dome, named here as 'Oseosan dome' because it is located around the Oseosan, the highest peak along the western coastal area, is composed mainly of the Neoproterozoic to Paleozoic ortho- and paragneiss, mafic metavolcanic rock, and metadolerite. Migmatization affected these rock units, in which leucocratic(granitic) materials derived from anatexis frequently occur as patch and vein parallel to or cutting through internal foliation. The Oseosan dome shows overall concentric geometry and outward-dipping internal foliation, but also partly complicatedly changeable or inward-dipping foliation. Taking available petrological and geochronological data into account, the Oseosan dome is interpreted to be exhumed quickly into the upper crustal level during the Late Triassic, accompanied in part with anatexis and granite intrusion. In addition, extensional shear zone intruded by the Late Triassic synkinematic granite and sedimentary basin have been reported around the Oseosan dome. These evidences possibly suggest that the Oseosan dome formed in closely associated with the Late Triassic extensional movement and diapiric flow. Alternatively, 1) thrust- or reverse fault-related doming or 2) interference between independent folds during structural inversion of the Late Traissic to Middle Jurassic sedimentary basin can be also considered as dome-forming process. However, considering the northern limb of the Oseosan dome, cutting by the Late Traissic granite, and the southern limb, cutting by contractional fault reactivated after the Middle Jurassic, it is likely that the domal structure formed during or prior to the Late Triassic.

• Economic and Environmental Geology
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• v.31 no.5
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• pp.415-424
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• 1998

In order to investigate soil-gas $^{222}Rn$ concentrations, Kwanak Campus (Seoul National University), Boeun (Choong-buk) and Gapyung (Kyonggi) areas were selected and classified depending on their base rock types. Radon risk indices of these study areas decrease in the order of Gapyung>Kwanak Campus>Boeun areas, and in the order of rock type as banded gneiss>granite gneiss>granite>black slate-shale>mica schist>shale-lirnestone>phyllite-schist. Radon emanating trends with water content and grain size of soils were assessed by modified Morse 3 min. method. Radon emanation increases with the increase of water content in soils which is lower than 6~16 wt.%, and decreases in the range of higher than 6-16 wt. %. It shows that Rn emanation increases with the decrease of soil grain size. Radioactivity analysis of radionuclides of 238U series in some soil samples shows that radioactive disequilibrium state between $^{226}Ra$ and $^{238}U$ exists owing to different geochemical behavior of each radionuclide, and, it is necessary to carry out radioactive isotope geochemical approach for soil-gas $^{222}Rn$ study.

• Journal of the Korean Geotechnical Society
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• v.28 no.11
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• pp.87-99
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• 2012

Targeting 9 types of rocks, which have high frequency of excavation, the researcher has analyzed decreasing behaviors of elastic modulus due to water content. The elastic modulus decreasing behaviors have been classified into 5 steps by uniaxial compressive strength. The results indicate that all of 5 sedimentary rocks and andesite show single decreasing behavior and granite, rhyolite, and gneiss demonstrate another decreasing behavior. Moreover, sensitivity of water content in granite, rhyolite, gneiss is almost twice as fast as that of the other rocks and their residual value of elastic modulus is very low.

• The Journal of Engineering Geology
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• v.18 no.4
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• pp.493-499
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• 2008

In order to evaluate the lateral behavior characteristics of single drilled shaft embedded in granite gneiss, a lateral load test was conducted in field. Horizontal displacement according to lateral load were measured along with the depth by an inclinometer installed in the shaft. In this study, We have evaluated horizontal displacement characteristics comparing the measurement values with calculating results by theoretical formula. Based on the comparison, the Chang's method was similar with the measurement values even though it was slightly underestimated. However, the finite analysis method and p-y method was overestimated, especially on the upper part of the ground.

• Economic and Environmental Geology
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• v.37 no.3
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• pp.355-364
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• 2004

A study on the weathering grade classification has been performed for granite and granite gneiss in Korea. The qualitative classification criteria of weathering were reviewed and then modified with field studies for the weathered rock masses. The thin section observations and XRD analyses for the different weathering grades rock samples showed the petrographical and petrophysical difference with respect to the weathering : the proportion of weathering-resistant minerals suck at quartz and orthoclase has a tendency to increase with the development of weathering, but that of weathering-sensible minerals such as anorthite and biotite is decreased. The ranges of physical and mechanical rock properties for different weathering grades were obtained from the laboratory rock tests and field tests for the studied rocks. And then, along with $RDI_{sq}$(Fookes et al., 1988), the weathering index $I_{a}$, (Woo, 2003) has been developed in this study to demarcate the weathering grade. Those two indices rely mainly on the water absorption ratio of rock and on the different rock strength. The range of these weathering indices have been determined with the physical and mechanical rock properties that can be obtained from simple field or laboratory tests in 4 grades $I_{a}$＞ 7 for F, 3.5 ＜ $I_{a}$ ＜ 10 for SW, 1.0 $I_{a}$＜ 6.0 for MW and $I_{a}$＜ 2.5 for HW. Consequently, the weathering index could be utilized to classify quantitatively the rock weathering grade, especially for the studied granites and the granite gneiss in Korea.

• Economic and Environmental Geology
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• v.18 no.1
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• pp.11-22
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• 1985

The Daehwa and Donsan tungsten-molybdenum deposits are composed of numerous fissure-filling veins developed in Precambrian gneiss and Cretaceous granite and quartz porphyry. K-Ar age of biotite in granite and that of muscovite in ore veins are $105{\pm}5\;Ma$ and 88.2~88.6 Ma respectively. Occurrence of ore deposits shows that relevant igneous rock is possibly quartz porphyry rather than above mentioned granite in temporal view point. Vein structure and mineralogy suggest that ore veins were formed by continuous vein filling, not by repeated mineralization. Three distinct depositional stages with decreasing age can be devided on the basis of mineral paragenesis and fluid inclusion studies: Stage I, deposition of oxides and silicates; stage II, deposition of base-metal sulfides and sulfosalts with carbonates; stage III, deposition of barren calcite and fluorite. Tungsten, molybdenum and tin mineralization occurred in stage I.

• Economic and Environmental Geology
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• v.15 no.2
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• pp.65-88
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• 1982

In the last ten years, marine geological and geophysical survey and research were conducted by Japanese, Russian and American scientists in the East Sea of Korea (Japan Sea). Many research results were published. However, regional research of the geology of the continental margin of the Korean Peninsula was not conducted. This study has made on attempt to classify submarine strata and stratigraphic boundaries. The study has revealed characters of submarine geology and structure. Isopach maps of each identified stratigraphic unit have been constructed as the results of this study. The study was conducted on the basis of analyses of marine seismic surveys carried out in the continental margin of the East Sea between Kangneung and Pohang. Three depositional basins were identified in the study area and they were named as, Mukho Basin, Hupo Basin and Pohang Basin. The Mukho Basin is developed in continental slope and shelf in the area between Kangneung and Samcheog. Quaternary and Pliocene sediments attain a maximum thickness of 900 m. Basement rocks are interpreted as granite and gneiss. They are correlated with granite-gneiss of the Taebaecksan Series of Pre-cambrian age and the Daebo granite of Jurassic age. The Hupo Basin is developed in the continental shelf between Uljin and Youngdeok. Quaternary and Pliocene sediments attain a maximum thickness of 600 m. Basement rocks were interpreted as granite and gneiss and they are correlated with metamorphic rocks of Pre-cambrian age and the Daebo granites, comprising the Ryongnam Massif. The Pohang Basin is developed in the area between Pohang and Gangu. This basin contains Miocene and older sediments. Basement rocks are not shown. Many faults are developed within the continental shelf and slope. These faults strike parallel with the coast line. A north-south direction is predominant in the southern study area. However, in the northern study area the faults strike north, and north-west. The faults are parallel to each other and are step faults down-thrown to the east or west, forming horst and graben structures which develop into sedimentary basins. Such faults caused the development of submarine banks along the boundary between the continental shelf and slope. This bank has acted as a barrier for deposition in the Hupo Basin. Paleozoic sedimentary rocks distributed widely in the adjacent land area are absent in the Mukho Basin. This suggests that the area of the basin was situated above the sea level until the Pliocene time. The study area contains Pliocene sediments in general. These sediments overlie the basement complex composed of metamorphic rocks, granites, Cretaceous (Kyongsang System) sedimentary rocks and Miocene sedimentary rocks. These facts lead to a conclusion that the continental shelf and slope of the study area were developed as a result of displacements along faults oriented parallel to the present coast line in the post Miocene time.

• Economic and Environmental Geology
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• v.32 no.3
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• pp.227-236
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• 1999

The Daeyou pegmatite is located at the central westerm part of the peninsula. Geology of the mine area consists mainy of pre-Combrian granite gneiss and leucoratic gneiss which are intruded by Mesozoic granites. The pegmatite deposits occur within granite gneiss. Most of pegmatites contain quartz, perthite, microcline-perthite, microcline, sodic plagioclase and tourmaline as dominant minerals with accessory minerals of mica (muscovite, biotite, sericite)and pyrite. Tourmaline occurs as four types: 1) unaltered single crystals, 2) patially sericitized grains bordered by sericite assemblage, 3) tourmaline intergrown with feldspar and qurtz grains, and 4) tourmaline introduced veinlet/ On the basic of optical, X-ray diffraction and chemical analysis, the composition of tourmaline mostly falls on the schorl-elbaite join, in the composition of tourmaline mostly falls on the schorl-elbraite join, in the composition of schorl end member from 0 to about 50%. In spite of the different occurrences, chemical composition of tourmaline shows the limited ranges as follows: $SiO_{2}$ (34.53~35.01 wt.%), $Al_{2}O_{3}$ (33.58~34.26wt.%), FeO (13.73~14.17wt.%), $Na_{2}O$ (1.60~1.72wt.%), MgO (0.56~0.72wt.%), MnO (0.12~0.18wt.%), CaO (0.02~0.06wt.%), $K_{2}O$(0.02~0.03wt.%) $TiO_{2}$ (0.02~0.05wt.%) and $Cr_{2}O_{3}$ (0.02~0.03wt.%). K-Ar ages of the muscovite and sericite fall between 1010$\pm$15 and 1074$\pm$16Ma and between 161.56$\pm$3.09 and 161.67$\pm$Ma, respectivrly. This means that hydrothrmal alteration occurred during middle Jurassic, whereas the pegmatite was initally formed during the late proterozoic age.