• The Journal of the Petrological Society of Korea
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• v.18 no.4
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• pp.349-370
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• 2009

The Mt. Dungjuribong Volcanic Complex located in Gurye-gun, southwest of Ryeongnam massif, composed of Cretaceous andesitic rocks and rhyolite. $SiO_2$ contents of the volcanic rocks range from 52.0 to 78.5 wt.%. The major and trace elements composition, REE patterns and tectonomagmatic discrimination diagrams of volcanic rocks suggest that they are typical of continental margin arc calc-alkaline rocks produced in the subduction environment. The phenocrysts of the volcanic rocks show that they had gone in disequilibrium state, such as reversal zoning and resorbed core of plagioclase, reaction rim around pyroxene and resorbed margins of quartz, which showing the evidence of magma mixing during the evolution of magma.

• Journal of the Korean Geophysical Society
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• v.3 no.3
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• pp.201-212
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• 2000

Recent seismicity of the central region of South Korea is investigated by using the micro-earthquake data recorded at the seismic network of KNUE(Korea National University of Education) since December, 1997. About two earthquakes are observed each month, which indicates relatively low seismic activities of the region, without showing any temporal characteristics of seismicity. The b-value of the region obtained from the data we used is found to be about 1.15. The epicenters of the micro-earthquakes are mostly located in the Okchon Zone, especially around Munkyong area, Poeun-Sokri Mt.-Youngdong area, and Kunsan-Nonsan area.

• The Journal of the Petrological Society of Korea
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• v.2 no.2
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• pp.130-138
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• 1993

Kyeonggi Gneiss complex forming Korean Precambrian basement is mainly composed of high-grade metasedimentary rocks, which are generally difficult to determine their absolute ages. We examined the feasibility of successive absolute age determination method for the marbles from this basement. We used hydrochloric acid for the selective dissolution of carbonate minerals from the marbles. Trace element analysis shows that most of Zr and Rb are concentrated in the residues. U in the residue is more abundant than that in HC1-dissolved parts. Pb, Sr, Sm, and Nd are somewhat evenly distributed between HC1-dissolved parts and the residues. }Th shows rather complex behavior. Sr isotopic compositions of the HC1-dissolved parts reveal mixing with Sr from non-carbonate minerals having much higher $^{87}Sr/^{86}Sr$ ratios. We suggest that the most reliable method in the age determination for the marbles of this area is measuring Pb isotopic ratios of the pieces of pure marbles.

• Economic and Environmental Geology
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• v.32 no.5
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• pp.537-544
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• 1999

In mineral exploration, there are many data sets which need to be created, processed and analyzed in order to discover a favorable mineralized zone. Recently, with Geographic Information System (GIS), such exploration data sets have been able to be systematically stored and effectively processed using computer technologies. In this study, most exploration data sets were first digitized and then rasterized. Furthermore, they were integrated together by using fuzzy set theory to provide a possibility map toward a target hypothesis. Our target hypothesis is "there is a skarn magnetite deposit in this study" and all fuzzy membership functions were made with respect to the target hypothesis. Test area is extended from 37:00N/l28:30E to 37:20N/I28:45E, approximately 20 km by 40 km. This area is a part of Taebaeksan mineralized areas, where the Sinyemi mine, a skarn magnetite deposit, is located. In final resultant map, high potential or possibility area coincides with the location of the Shinyemi mine. In this regard, we conclude the fuzzy set theory can be effectively applied to this study and provides an excellent example to define potential area for further mineral exploration.

• Economic and Environmental Geology
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• v.41 no.2
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• pp.173-181
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• 2008

CHIME ages were obtained from monazites in metamorphic rocks from the Seosan and Siheung Groups in the Gyeonggi gneiss complex, Korean peninsula. Monazite CHIME ages range from 234 to 257 Ma, corresponding to the late Permian to middle Triassic Songrim disturbance due to the collision event between the North and South China blocks within the Gyeonggi gneiss complex in the Korean peninsula. The CHIME ages are consistent with the metamorphic ages from the Hongseong area (231 Ma, Kim et al., 2006) and the Odesan area (245-248 Ma, Oh et al., 2006b) in the Gyeonggi gneiss complex and are older than those from the Dabie-Sulu collision belt (220${\sim}$242 Ma, Yang or of., 2003; Liu et al., 2003, 2004) suggesting that the collision between the North and South China blocks had occurred earlier in Korea than China.

• The Journal of the Petrological Society of Korea
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• v.5 no.2
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• pp.168-187
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• 1996

In the study area Uanggunbong-Samgunri area), Precambrian metamorphic complex, (Taebacksan gneiss complex, Hyundong gneiss complex, and Taebacksan schist complex) had undergone three different regional metamorphisms at least before Paleozoic. The Paleozoic sediments in the study area also had undergone three different metamorphisms at least. The first is low pressure type regional metamorphism, the second is low pressure type contact metamorphism due to the intrusion of Chunyang granite, and the last is medium pressure type metamorphism caused by thrust in south of Janggunbong area. The first metamorphism formed the prevailing metamorphic zones in the Paleozoic metasediments and the metamorphic grade of the first regional metamorphism increases from the chloritoid zone, through the staurolite zone, garnet zone, staurolite+biotite zone, and to the andalusite+biotite zone. The second metamorphism affected both Pre-Cambrian and Paleozoic metasediments located close to the Chunyang granite. The effect of the contact metamorphism is restricted to the very narrow zone around the granite. The third metamorphism that produced kyanite, is restricted to the very narrow region near the thrust fault in the south of Janggunbong with an E-W trend.

• The Journal of the Petrological Society of Korea
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• v.22 no.2
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• pp.197-208
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• 2013

The Namwon and Sunchang granites are neighbouring plutons intruding the Yeongnam massif and the Okcheon metamorphic belt, respectively in the southwestern part of the Korean peninsula. In this study, SHRIMP zircon U-Pb ages are determined from these plutons. The results show that the emplacement age of the Namwon granite is $185.8{\pm}0.9(2{\sigma})$ Ma. We obtained $175.0{\pm}2.0(2{\sigma})$ Ma from the northern part and $179.8{\pm}0.9(2{\sigma})$ Ma from the central part of the Sunchang granite, yielding $177.4{\pm}1.3(2{\sigma})$ Ma as the average age of the pluton. Such age results confirm that the Honam shear zone, which cause marked deformation of the Sunchang granite, was active after ca. 175 Ma.

• The Journal of Engineering Geology
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• v.13 no.3
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• pp.293-308
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• 2003

New results about the crustal structure down to a depth of 60 km beneath North Korea were obtained using the seismic tomography method. About 1013 P- and S-wave travel times from local earthquakes recorded by the Korean stations and the vicinity were used in the research. All earthquakes were relocated on the basis of an algorithm proposed in this study. Parameterization of the velocity structure is realized with a set of nodes distributed in the study volume according to the ray density. 120 nodes located at four depth levels were used to obtain the resulting P- and S-wave velocity structures. As a result, it is found that P- and S-wave velocity anomalies of the Rangnim Massif at depth of 8 km are high and low, respectively, whereas those of the Pyongnam Basin are low up to 24 km. It indicates that the Rangnim Massif contains Archean-early Lower Proterozoic Massif foldings with many faults and fractures which may be saturated with underground water and/or hot springs. On the other hand, the Pyongyang-Sariwon in the Pyongnam Basin is an intraplatform depression which was filled with sediments for the motion of the Upper Proterozoic, Silurian and Upper Paleozoic, and Lower Mesozoic origin. In particular, the high P- and S-wave velocity anomalies are observed at depth of 8, 16, and 24 km beneath Mt. Backdu, indicating that they may be the shallow conduits of the solidified magma bodies, while the low P-and S-wave velocity anomalies at depth of 38 km must be related with the magma chamber of low velocity bodies with partial melting. We also found the Moho discontinuities beneath the Origin Basin including Sari won to be about 55 km deep, whereas those of Mt. Backdu is found to be about 38 km. The high ratio of P-wave velocity/S-wave velocity at Moho suggests that there must be a partial melting body near the boundary of the crust and mantle. Consequently we may well consider Mt. Backdu as a dormant volcano which is holding the intermediate magma chamber near the Moho discontinuity. This study also brought interesting and important findings that there exist some materials with very high P- and S-wave velocity annomoalies at depth of about 40 km near Mt. Myohyang area at the edge of the Rangnim Massif shield.

• Journal of the Korean earth science society
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• v.22 no.6
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• pp.528-547
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• 2001

The blastoporphyritic granite gneiss (BPGN) including much alkali-feldspar megacrysts occurs in Jiri mountains area, southwestern part of Sobaegsan massif, Korea. The BPGN is formed gneiss complexes with other gneisses in Precambrian. The BPGN was named as porphyroblastic gneiss with porphyroblasts of alkali-feldspar megacrysts by other researchers, but the BPGN includes of euhedral alkali-feldspars (microcline), and the boundary with the granitic gneiss represents sharp contact as intrusive relationship. The BPGN mainly composes of alkali-feldspar megacrysts, quartz, plagioclase, K-feldspar and biotite some almandine and accessary minerals are muscovite, chlorite, apatite, zircon and opaques. The alkali-feldspar is microcline with perthitic texture. An content of plagioclases show 30 to 40. Biotites occur two type, one is Brown biotite which shows compositional ranges of Mg/Fe+Mg ratios from 0.38 to 0.52, the other is Green Bt. which is retrograde product. Camels to be various sizes and shapes have composition of almandine with 73 to 80 mole percent, but represent retrogressive zoning from core (X$_{pyr}$: 15.9${\sim}$20.8) to rim (X$_{pyr}$:13.7${\sim}$15.9) to be evidence of retrograde metamorphism. Megacrysts of alkali-feldspar in the BPGN show rectangular shape of euhedral and some become ellipsoidal or spheroidal in shape and the average size up to 20 cm long. The megacryst includes of biotite, plagioclase and quartz, and rarely euhedral apatite as inclusions. In petrochemistry the BPGN represents granodiorite composition, characteristics of peraluminous S-type granitoid and calc-alkaline features.

• Journal of the Korean earth science society
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• v.28 no.2
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• pp.187-201
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• 2007

The first magnetotelluric (MT) transect across the Korean Peninsula was obtained traversing from the East Sea shoreline to the Yellow Sea shoreline. The MT survey profile was designed perpendicular to the strike of the principal geologic structure of the Korean Peninsula $(N30^{\circ}E)$, so-called 'China direction'. MT data were achieved at 50 sites with spacings of $3{\sim}8km$ along the 240 km survey line. The impedance responses are divided into four subsets reflecting typical geological units: the Kyonggi Massif, the Okchon Belt, the western part of the Kyongsang Basin, and the eastern part of the Kyongsang Basin. In the western part of the Kyongsang Basin, the thickness of the sedimentary layer is estimated to be about 3 km to 8 km and its resistivity is a few hundred ohm-m. A highly conductive layer with a resistivity of 1 to 30 ohm-m was detected beneath the sedimentary layer. The MT data at the Okchon Belt show peculiar responses with phase exceeding $90^{\circ}$. This feature may be explained by an electrically anisotropic structure which is composed of a narrow anisotropic block and an anisotropic layer. The Kyonggi Massif and the eastern part of Kyongsang Basin play a role of window to the deep geoelectrical structure because of the very high resistivity of upper crust. The second layers with highest resistivities in 1-D conductivity models occupy the upper crust with thicknesses of 13 km in the Kyonggi Massif and 18 km in the eastern Kyongsang Basin, respectively.