• The Journal of the Petrological Society of Korea
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• v.28 no.2
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• pp.129-141
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• 2019

The Eoraesan area, Chungju, which is located in the northwestern part of Ogcheon Metamorphic Zone, Korea, mainly consists of the Neoproterozoic Gyemyeongsan Formation and the Mesozoic igneous rocks which intruded it. The metaacidic rocks (MAR) of the Gyemyeongsan Formation show a maximum radioactive value, and the Early Jurassic biotite granite is regionally distributed in this area. In this paper is researched the microstructure related to the growth of rare-earth mineral of allanite in the MAR, and is considered the source and occurrence time of rare-earth element (REE) mineralization. The MAR is mainly composed of alkalic feldspar (mainly microcline), quartz, iron-oxidizing mineral, biotite, muscovite, plagioclase, hornblende, allanite, zircon, epidote, fluorite, apatite, garnet, (clino)zoisite etc. The radioactive elements contained in the allanite cause a dark brown hale in the surrounding biotite, and the allinte also occurs as aggregate along the regional foliation. The deflection of regional foliation and the strain shadows, which are common to the pre-tectonic porphyroblast grown before the formation of regional foliation, can't be observed around most allanites (aggregates). The grain size and orientation of ironoxidizing mineral included in the allanite aggregate are the same as those in the matrix. It is recognized the hydrothermal conversion of hornblende to biotite due to the intrusion of igneous rock, and the secondary biotite occurs and contacts with allanite, zircon, epidote etc. These microstructures indicate that the rare-earth mineral of allanite (aggregate) grew by the hydrothermal alteration due to the intrusion of igneous rock after the formation of regional foliation. It is considered that the REE mineralization is closely related to the intrusion of Early Jurassic biotite granite which is regionally distributed in this area.

• The Journal of Engineering Geology
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• v.13 no.2
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• pp.207-225
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• 2003

According to the data analysis of the regional fracture systems in southern Korea, the fracture orientations show three dominant sets : NNE, NW and WNW. A NNE set is the most abundant and includes most of the largest fractures. The highest fracture density is shown in the Taebaegsan mineralized area corresponding to Ogchon nonmetamorphic belt and the lowest one in the southwestern area of southern Korea. In addition, the density is higher in nonmetamorphic sedimentary rocks such as Choseon Supergroup. Pyeongan Supergroup, Daedong Supergroup and Kyeongsang Supergroup than in Precambrian basements and Jurassic granites. The regional fractures in southern Korea can be classified into four orders designated $F_1,{\;}F_2,{\;}F_3{\;}and{\;}F_4${\;}and{\;}F_4$ on the basis of their trace length. It is quite significant that fractures of each order are self-similar with respect to orientation and the combined fracture length distribution indicates a power-law distribution with an exponent of -2.04. As fractures were analyzed based on the tectonic provinces, Gyeonggj Massif and Kyeongsang Basin have all orders of fractures from $F_1$ to $F_4$. Most of the large scale faults may be ascribed to the products of slip accumulation through multiple deformation. Others besides $F_1$ fractures are thought to be evenly distributed through the whole area of southern Korea.

• Proceedings of the Mineralogical Society of Korea Conference
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• 2003.05a
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• pp.55-55
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• 2003

호남전단대는 옥천대 남서부지역에 북동 내지 북북동 방향으로 발달하는 일련의 우수향 연성전단대로 한반도를 포함하는 동북아 지역의 중생대 부가작용과 관련하여 매우 중요한 조구조적 요소이며, 특히 북중국 대륙과 남중국 대륙이 유라시아 대륙에 부가되는 과정과 관련하여 동북아 지역의 중생대 지체구조 발달사를 설정하는데 매우 중요하게 생각되고 있다. 그러나 이러한 조구조적 중요성에도 불구하고 호남전단대의 정확한 운동 시기는 아직 밝혀지지 않고 있다. 이번 연구는 전주전단대가 지나가는 김제 금산사 지역과 무안 지역에 분포하는 화강암류를 대상으로 SHRIMP U-Pb 저어콘 연대 측정을 실시하여 전단운동시기를 밝혔다. 금산사 지역은 엽리상 각섬석-흑운모 화강섬록암이 흑운모 화강암에 포획된 명확한 지질학적 증거를 보이고 있는 곳으로 화강섬록암의 U-Pb 저어콘 연대는 172.7 $\pm$ 1.4 Ma이며 화강암의 연대는 169.6 $\pm$ 1.8 Ma과 167.5 $\pm$ 2.4 Ma로 구해졌다. 따라서 전주전단대의 전단운동은 약 173 - 170 Ma 기간에 일어났다. 특히 화강암 내에 포획된 화강섬록암 내에는 전반적인 우수향 전단운동 후기에 관입한 다수의 석영질 맥이 좌수향의 전단운동을 받은 증거가 관찰되는데 이러한 사실은 우수향의 전단운동 이후 화강암의 관입 이전에 좌수향의 전단 운동이 있었음을 지시한다. 무안 지역은 전주전단대의 끝 부분에 해당하는 곳으로 각섬석화강섬록암과 이를 관입한 각섬석화강암이 모두 우수향의 전단운동을 받았다. 화강섬록암의 U-Pb 저어콘 연대는 176.3 $\pm$ 1.7 Ma이며 화강암의 연대는 165.8 $\pm$ 2.0 Ma로 구해졌으며, 따라서 최종 우수향 전단운동의 시기는 166 Ma 이후로 생각된다. 무안 지역에 분포하는 화강섬록암과 화강암의 관입시기는 금산사 지역의 화강섬록암과 화강암과 각각 조화적이다. 호남전단대의 운동 시기를 밝히기 위해 전주전단대에 해당하는 금산사 지역과 무안 지역에 분포하는 화강암류에 대한 U-Pb 저어콘 연대 측정을 실시한 결과 호남전단대의 특징적인 우수향 전단운동은 적어도 2회에 걸쳐 일어났음을 알 수 있다. 즉 첫 번째 광역적인 전단운동은 약 173 - 170 Ma 시기에 일어났으며, 두 번째 전단운동은 166 Ma 이후에 일어났음을 알 수 있다. 한편 전기의 우수향 전단운동은 후기 화강암 관입 이전에 좌수향 전단 운동에 의해 부분적으로 재활성 되었으며, 후기 화강암의 관입 이후에 재차 우수향 전단운동으로 활성화 되었음을 알 수 있다. 이상의 결과를 종합하면 호남전단대는 쥬라기 중기에 발생한 광역적인 우수향의 연성전단운동이나, 운동 특성은 연속적이기 보다는 단속적으로 일어난 것으로 생각된다.

• Economic and Environmental Geology
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• v.50 no.6
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• pp.445-466
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• 2017

Yeongdong area is located in the contact zone between central southeastern Ogcheon belt and Yeongnam massif, in which Cretaceous Yeongdong basin exists. Therefore, the study area has complex geological environment of various geological age and rock types such as Precambrian metamorphic rocks, age-unknown Ogcheon Supergroup, Paleozoic/Mesozoic sedimentary rocks, Mesozoic igneous rocks and Quaternary alluvial deposits. This study focuses on the link between the various geology and water type, and discussed the source of some major ions and their related water-rock interaction. For this study, the field parameters and ion concentrations for twenty alluvial/weathered and eighty bedrock aquifer wells were used. Statistical analysis indicates that there was no significant differences in groundwater quality between wet and dry seasons. Although various types were observed due to complex geology, 80 to 84 % of samples showed $Ca-HCO_3$ water type. Some wells placed in alluvial/weathered aquifers of Precambrian metamorphic and Jurassic granitic terrains showed somewhat elevated $NO_3$ and Cl concentrations. $Mg-HCO_3$ typed waters prevailed in Cretaceous Yeongdong sedimentary rocks. The deeper wells placed in bedrock aquifers showed complicated water types varying from $Ca-HCO_3$ through $Ca-Cl/SO_4/NO_3$ to $Na-HCO_3$ and Na-Cl type. Groundwater samples with $Na-HCO_3$ or Na-Cl types are generally high in F concentrations, indicating more influences of water-rock interaction within mineralized/hydrothermal alteration zone by Cretaceous porphyry or granites. This study revealed that many deep-seated aquifer had been contaminated by $NO_3$, especially prominent in Jurassic granites area. Based on molar ratios of $HCO_3/Ca$, $HCO_3/Na$, Na/Si, it can be inferred that Ca and $HCO_3$ components of most groundwater in alluvial/weathered aquifer wells were definitely related with dissolution of calcite. On the other hand, Ca and $HCO_3$ in bedrock aquifer seem to be due to dissolution of feldspar besides calcite. However, these molar ratios require other mechanism except simple weathering process causing feldspar to be broken into kaolinite. The origin of $HCO_3$ of some groundwater occurring in Cretaceous Yeongdong sedimentary rock area seems to be from dissolution of dolomite($MgCO_3$) or strontianite($SrCO_3$) as well.

• Economic and Environmental Geology
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• v.55 no.6
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• pp.649-659
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• 2022

This study examined the granite, quartzite, phyllite, schist, and gneiss as aggregate resources among the original rock distributed in the Chungju-Goesan area. The granite distributed in the study area is mainly composed of Jurassic biotite granite, and the quartzite layer is from the Daehyangsan quartzite Formation distributed on the upper part of the Gyemyeongsan Formation and the Hyangsan-ri dolomitic limestone Formation. In addition, phyllite is pophyrytic phyllite-schist from the Hwanggangri Formation of the Okcheon group, schist is chlorite schist, from the Munjuri Formation of the Okcheon group, and gneiss is porphyroblastic gneiss which is the upper part of the Seochangri Formation. Aggregate quality evaluation factors of these rocks included fineness modulus, absorption, unit weight, absolute dry density, solid content, porosity, resistance to abrasion, and soundness. In the case of granite, it was found to be partially unsatisfactory in terms of unit weight, solid content, porosity, and resistance to abrasion. Gneiss was found to be out of the standard values in resistance to abrasion and schist in porosity and solid content. As for the overall quality of aggregate resources, it was analyzed that quartzite, gneiss, and phyllite showed excellent quality. Aggregate quality tests are performed simply for each rock, but the rock may vary depending on the morphology of the mineral. Therefore, when analyzing and utilizing the quality evaluation of aggregate resources, it will be possible to use them more efficiently if the rock-mineralological research is performed together.

• The Journal of the Petrological Society of Korea
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• v.9 no.1
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• pp.13-28
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• 2000

Chojeong area is mainly composed of the Ogcheon Group which consists of regionally metamorphosed, age-unknown sedimentary rocks. In the northwestern parts, the Group is intruded by the Jurassic Daebo granite and Cretaceous felsic and mafic dykes. The lowermost, Midongsan Formation which consists of milky white impure quartzite, crops out along the anticline axes with N40E trend. Ungyori quartzite Formation is intercalated with quartzite and slate. Miwon Formation is most widely exposed in the area and consists mainly of phyllitic sandy rocks with a thin crystalline limestone bed. Hwajeonri Formation is divided into two parts, pelitic lower and calcareous upper parts, composed with phyllite and slate. Changri and Hwanggangri Formations are typical members of Ogcheon Group, the former bearing coally graphite seams consists mainly of black slate and phyllite with intercalated greenish grey phyllite, the latter is pebble bearing phyllite formation of which matrix and pebbles are variable in compositions and size. Biotite granite, porphyritic granite and two mica granite belong to Jurassic so-called Dabo granite. They intruded the Ogcheon Group forming vast contact metarnophic zone. Quartz porphyry, mafic dyke and felsite intruded along the marginal zone of porphyritic granite batholith and fracture of NS trend. Main structural lineaments in Ogcheon Group shows N25-45E, NS and N30-45W trends. The N25-45E trends are mainly from general ductile deformation during regional metamorphism, showing isoclinal folding, Fl foliations and lithological erosional characters. Some of these trends are due to normal faults. The NS and N30-45W trends represent brittle deformation including faults and joints. In the area of granitic batholith, NS to N30- 45 trends are from the direction of dykes. In the soils of the area, average contents of heavy metal elements such as Cd, Cr, Cu, Pb, and Zn are 0.2, 50.6, 35.5, 27.9, and 93.4 ppm respectively, which are not higher than the average values of natural soils, under the tolerable level. Enrichment Index does not show any heavy metal pollution in the area. Average depths of weathering(5m vs. 2m), porosities(43.94 vs. 51.80), densities(l.29 vs. 1.15), and permeabilities(2.52 vs. 8.07) are comparable in granite areas and in the phyllite areas of Ogcheon Group.

• Economic and Environmental Geology
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• v.8 no.4
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• pp.223-230
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• 1975

South Korea is divided tectonically into four segments. The Kyonggi-Ryongnam massif is composed of Precambrian schists and gneisses and consititutes a base for the succeeding formations. The Okcheon geosynclinal zone in the Kyonggi-Ryongnam massif strectches from southwest to northeast diagonally across the peninsula in a direction known as the Sinian direction. Its northeastern part is composed primarily of Paleozoic to early Mesozoic sedimentary formations and the southwestern part of the late Precambrian Okcheon metamorphic series. The Kyongsang basin occupies the southeast and southwest of the peninsula and is made up of a thick series of Cretaceous terrestrial sedimentary and andesitic rocks. A few small Tertiary basins are scattered in the eastern coastal area and in Cheju Island, and are composed of marine sedimentary and basaltic rocks. Jurassic Daebo granites intrude the Kyonggi-Ryongnam massif and the Okcheon zone in the Sinian direction, whereas late Cretaceous Bulkuksa granites are scattered randomly in the Kyongsang basin.

• Journal of the Korean earth science society
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• v.21 no.3
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• pp.302-314
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• 2000

Keumseong area in the southern part of the Jecheon city, the Ogcheon Belt, consists of Precambrian Dangdusan Metamorphic Complex, Dori Formation of the Choseon Supergroup, and Jurassic Jecheon Granite. The Dangdusan Metamorphic Complex consists of quartz schist, mica schist. quartzite and pegmatite. The Dori Formation is composed of mainly laminated limestone. The rocks in the study area have been undergone at least three phases of deformations since Paleozoic period. The Dangdusan Metamorphic Complex is outcrop at three areas in the study area, which are exposed along the faults and occurred as inlier within the Dori Formation. Previous authors interpreted the uplift of the Dangdusan Metamorphic Complex by the Dangdusan Fault, but we could not find any evidences related to the Dangdusan Fault. Thus, we interpret the uplift of the Dangdusan Metamorphic Complex due to the D$_2$ Weolgulri and Dangdusan thrusts and post-D$_2$ Jungbodeul, Kokyo and Jungjeonri faults. The uplift of the Busan Metamorphic Complex to the west of the study area was interpreted by ductile deformation. However, the Dangdusan Metamorphic Complex is formed by brittle thrusts and faults in this study. According to deformation sequence, the characters of deformations in the Choseon and Ogcheon suprergroups had been changed from ductile to brittle deformations through the time. Therefore, we interpret the Dangdusan Metamorphic Complex is exposed later than the Busan Metamorphic Complex.

• The Journal of the Petrological Society of Korea
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• v.7 no.2
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• pp.69-76
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• 1998

$^{40}Ar/^{39}Ar$ analytical data of hornblende and muscovite separates from granitic rocks in southwestern region of Ogcheon belt shows fellowing tectonic implication, $^{40}Ar/^{39}Ar$ data of 5 samples yield apparent age spectra and $^{37}Ar_{ca}/^{39}Ar_k$ and $^{38}Ar_{CI}/^{39}Ar_k$ plateaus for more than 60% of the $^{39}Ar$ release. Except for HN-100, the $^{36}Ar/^{40}Ar$ versus $^{39}Ar/^{40}Ar$ corelalation diagrams indicate the presence of one distint line. Muscovite of sample PKJ-44 yield flate apparent age plateau for > 60% of the $^{39}Ar_k$ release. In the high temperature steps, the $^{37}Ar_{ca}/^{39}Ar_k$ values are irregular with a correlative increase in $^{38}Ar_{CI}/^{39}Ar_k$, suggesting some Ca and CI rich phase, tapped between the silicate sheet is being argon degassed. The $^{40}Ar/^{39}Ar$ total gas age and the high temperature age of HN-100 is 918.2 Ma and 1360 Ma, respectively. The former affectted by recystallized age of Daebo Orogeny, and the latter indicated age of hornblende closure temperature for cooling stage of amphibole xenolith in granite gneiss. Three rock types of Kwangju granites show about 165 Ma hornblende and muscovite ages with some degassed argon at low temperature steps. These ages of 4 samples indicate also recrystallized age by Daebo Orogeny. In $^{40}Ar/^{39}Ar$ mineral age, Rb/Sr whole age and K/Ar mineral age, discordant ages of southwestern region of Ogcheon belt suggesting cooling rates approaching 3~4$^{\circ}C$/m. y. Such slow cooling rates can be produced by uplift rate of 100m/m.y. or slightly slower than isothem-migration rate derived from the hornblende samples. We conclude that the strongest Orogeny and igneous activity of southwestern region of Ogcheon belt are middle proterozoic era (about 1360 Ma) and middle Jurassic period (about 165 Ma).

• Journal of the Korean earth science society
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• v.22 no.1
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• pp.1-9
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• 2001

Composition of the major and trace elements, Rb-Sr isochron age Sr-Nd isotope composition were determined for foliated in the Jeonju area, in the middle part of the Ogcheon Fold Bet, Korea. The geochemical characteristics of the Jeonju foliated granite indicate that the granite had been crystallized from a calc-alkaline series, and formed in a volcanic are environment. The isotopic compositions of the Jeonju foliated granite give Rb-Sr whole rock errorchron age of 168.2${\pm}$8 Ma(2${\sigma}$), corresponding to the middle Jurassic period, with the Sr initial ratio of 0.71354${\pm}$0.00031. $^{143}$Nd/$^{144}$Nd ratios, ${\varepsilon}$Nd and ${\varepsilon}$Sr values range from 0.511477 to 0.511744, -15.4${\sim}$-21.2, and +108.8${\sim}$+l42.6, respectively. Model ages were caculated to be 1.82${\sim}$2.89Ga. The isotopic data of Jeonju foliated granite indicate that the source material may have been derived from partial melting of continental crust materials.