• Economic and Environmental Geology
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• v.14 no.2
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• pp.55-76
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• 1981

Southwestern contact zone of the Boeun granodiorite occurs near the thrust fault between the Ogcheon Group and Majeonri Limestone Formation. Ogcheon Group, metasediments composed of the Munjuri Formation, Changri Formation, and unconformably overlying Hwanggangri Formation, belongs to greenschist facies of regional metamorphism accompanied with deformation of two fold axes, $N10^{\circ}E$ and $N45-65^{\circ}E$ directions. Basic metamorphic rocks occurring in the Changri and Limestone Formations are the meta-basalts and meta-diabases of tholeiitic basalt series. The meta-basalts intruded in the Changri Formation as sills, whereas the meta-diabases in the Changri and Limestone Formations as stocks in appearance. They are considered to have emplaced before the formation of two fold axes and related with the thrust fault, based on the geologic setting of the area. The metamorphic facies are identified to be greenschist facies to epidote-amphibolite facies for the meta-basalt, and epidote-amphibolite facies for the meta-diabases. It is interpreted that such a variety of facies was related from the combination of earlier deuteric alteration and later regional metamorphism. The metasediments in southwestern contact zont of the Boeun granodiorite which is a product of later syntectonic intrusion of middle Jurassic in age, show pyroxene-hornfels facies near the contact and amphibole-horenfels facies away from the contact to the mineral zoning in the contact metamorphic aureole of the Limestone Formation, based on the paragenetic analysis of mineral assemblages. The Limestone in the area appears to be considerably $SiO_2-CaO-MgO-CO_2-H_2O$ can be adopted to evaluate equilibrium conditions of the mineral assemblages in each mineral zone. It is revealed that a temperature gradient was existed accross the contact aureole ranging from the higher igneous side to lower sedimentary side, whereas no clear trend of $XCO_2$ variation appears but high mole fraction. The tremolite diopside-quartz-calcite assemblages occurs in common through the most mineral zones of contact aureole that is in good agreement with the equivalent reaction curve which extends over a wide range of $T-XCO_2$ conditions.

• The Journal of the Petrological Society of Korea
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• v.23 no.2
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• pp.105-117
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• 2014

The Ogcheon and Joseon Supergroups are distributed in the Bonghwajae area, Jecheon-si, Chungcheongbuk-do, Korea which is located in the northeastern fore-end of the Ogcheon Metamorphic Zone. This paper researched the geological structures based on the geometric and kinematic characteristics and the forming sequence of the major multi-deformed rock and microstructures. Most of regional foliations are not the S0 bedding but the S0-1 composite foliations defined by the preferred orientation of stretching minerals, some are recognized as the S0-1-2 composite foliations by the preferred orientation of insoluble opaque minerals and cleavage lamella. The geological structures were formed at least by three phases of deformations i.e. NNE-SSW trending D1, E-W trending D2, N-S trending D3 compressions. The S0-1 composite foliation, which shows a similar zone-distribution trend of the constitution strata of the Ogcheon and Joseon Supergroups, trended WNW before D2 deformation, but it was reoriented into N-S which was parallel to the trend of S2 foliation by D2 deformation, and it was rearranged into NW, NE, N-S trends as it is now by D3 deformation. The structural characteristics of each deformation phase and the deformation history are very similar to those in the eastern domain of Busan area into which the Ogcheon and Joseon Supergroups in this area are extended as NNW trend. It is expected to be very valuable data in interpreting the tectonic evolution of the northeastern fore-end of the Ogcheon Metamorphic Zone.

• The Journal of the Petrological Society of Korea
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• v.10 no.2
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• pp.106-120
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• 2001

The Busan area in the northeastern part of the Ogcheon metamorphic zone, Korea, consists mainly of Precambrian Busan and Bakdallyeong gneiss complexes, Ogcheon metamorphic rocks and Mesozoic granitoids. The Busan gneiss complex shows Heart-shaped distribution laying down eastward, and is surrounded by the Ogcheon metamorphic rocks in the central part of the Busan area. In this study structural examination on the main constituent rocks (Busan gneiss complex and Ogcheon metamorphic rocks) was conducted to clarify the geological structure of the Ogcheon metamorphic zone in the Busan area. It indicates that the geological structure was formed at least by three phases of deformation. (1) Dl deformation: the formative period of the structural units of WNW trend (Sanjeoteo, Busan-II, Busan-I, and Chungiu nappes) and the mylonitic foliations related to the compression of NNE-SSW direction, (2) D2 deformation: the differential E-W shortening and N-S extension period of the structural units of WNW trend related to the compression of E-W or WNW-ESE directions, (3) D3 deformation: the formative period of the kink or open folds of E-W trend related to the compression of N-S direction in the eastern and southern parts of Busan area where the structural units of N-S or NNE trends reoriented owing to the intense D2 deformation were developed. These three phases of deformation are closely connected with the distribution of the structural units and the Heart-shaped Busan gneiss complex laying down eastward, and in this paper a new geodynamic model to the Heart-shaped Busan gneiss complex is suggested: Dl deformation-the zonal distribution of WNW trend with a constant width, D2 deformation - the formation of convex wedges northeastward and southward, D3 deformation - the formation of concave wedge westward.

• The Journal of the Petrological Society of Korea
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• v.6 no.2
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• pp.133-149
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• 1997

In the metapelites around the Ogcheon granite, the metamorphic grade increases from the biotite zone through the andalusite zone to the sillimanite zone towards the intrusion contact. In the metabasites around the Boeun granite, the metamorphic grade increases from transitional zone between the greenchist and amphibolite facies through the amphibolite facies to the upper amphibolite facies towards the intrusion contact. In the Doiri area locating near the intrusion contact of the Boeun granite, sillimanite- and andalusite-bearing metapelites are found with in 500 m away from the contact. The evidence described above indicates that the Ogcheon and Boeun granites caused low-P/T type contact metamorphism to the country rocks. The P-T condition of contact metamorphism due to the intrusion of the Ogcheon granite is $540{\pm}40^{circ}C, 2.8{\pm}0.9$ kb. The temperature condition of contact metamorphism due to the intrusion of the Boeun granite is $698{\pm}28^{\circ}C$. The wide compositional range of amphibole and plagioclase in the metabasites around the Boeun granite is due to the immisibility gab of amphibole and plagioclase and unstable relict composition resulted from an incomplete metamorphic reaction. The compositional range of stable amphibole and plagioclase decreases as a metamorphic grade increases due to a close of immiscibility gab. The thermal effect of contact metamorphism due to the intrusion of the Ogcheon and Boeun granites, are calculated using the CONTACT2 program based on a two dimensional finite difference method. In order to estimate the thermal effect of an introduced pluton, a circle with 10 km diameter and a triangle with 20 km side are used for the intrusion geometries of the Ogcheon granite and the Boeun granite, respectively. The results from the field and modeling studies suggest that the intrusion temperatures of the Ogcheon granite close to $800^{\circ}C$ and the intrusion temperature of the Boeun granite is higher than $1000^{\circ}C$. However, the intrusion temperatures can be lower than the suggested temperature, if the geothermal gradient prior to the intrusion of the Ogcheon and Boeun granites was higher than the normal continental grothermal gradient.

• Economic and Environmental Geology
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• v.50 no.5
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• pp.353-361
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• 2017

Uranium concentration in groundwater of the Goesan area was anticipated high because the area contains Ogcheon metamorphic rock zone which partly includes coal bed bearing high uranium content and nearly half of the area is covered by granitic rocks. Groundwater samples collected from 250 wells in five 5 lithology (Ogcheon meta-sandy rock zone (Og1), Ogcheon lower phyllite zone (Og2), Ogcheon pebble bearing phyllite zone (Og3), Jurassic granite (Jgr), Cretaceous granite (Kgr)), of the area were analyzed and equivalent uranium concentrations (e(U)) from 200 rocks near sampled wells were measured using portable gamma spectrometry. Higher median value of e(U) (8.2 mg/kg) was found on Kgr outcrops. The median e(U) value of Og2 was not as high as that of Kgr and similar to those of Jgr, Og1, and Og3 (3.05~3.90 mg/kg). The uranium level in groundwater of the area ranged from 0.01 to $293.0{\mu}g/L$ with a median value of $0.87{\mu}g/L$ which is similar to the national median uranium level of $0.74{\mu}g/L$. The uranium concentration was high in the samples from the Kgr (median $4.74{\mu}g/L$) and low samples from the Og1, Og2, and Og3 (median $0.35{\sim}0.74{\mu}g/L$). The percentage of total samples having uranium level above $30{\mu}g/L$ was 2.8%, on the other hand, that of Kgr is 20.7%, reflecting additional survey on the Kgr area is needed.

• The Journal of the Petrological Society of Korea
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• v.10 no.2
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• pp.57-81
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• 2001

In the amphibolites of the Hwanggangri area, three metamorphic zones are established like hornblende-actinolite zone (H-AZ), hornblende zone (HZ) and diopside zone (DZ) by the main mineral assemblages. Hornblende zone and hornblende-actinolite zone develope away from the diopside zone that experienced the highest thermal effect. Thus, this pattern identifies the decreasing metamorphic grade of the contact metamorphism with increasing distance from the granitic pluton. The mineral assemblages of this rock are classified into six representative groups such as $\circled1$ actinolite+plagioclase+chlorite, $\circled2$ actinolite+hornblende+plagioclase+chlorite$\pm$epidote$\pm$biotite, $\circled3$ actinolite+hornblende+plagioclass$\pm$biotite$\pm$epidote, $\circled4$ hornblende+plagioclase$\pm$biotite$\pm$chlorite, $\circled5$ hornblende+plagioclase+diopside+actinolite$\pm$epidote$\pm$chlorite, $\circled6$hornblende+plagioclase+diopside$\pm$biotite$\pm$epidote. Two metamorphic events m recognized in the amphibolites of the study area that the first metamorphism is the regional metamorphism dominantly occurred in the whole Ogcheon metamorphic belt and it gave rise to the growth of actinolite at the core or center of the amphibole grains of coarse and medium size. Its metamorphic grade ranges from the greenschist facies to epidote-amphibolite facies. The second metamorphism overlapped is the contact metamorphism caused by the adjacent granitic pluton, and its metamorphic grade is thought to reach to the low pressure part of upper amphibolite facies. According to the calculation by TWEEQU thermobarometry and amphibole-plagioclase thermometry, the metamorphic temperature of initial regional metamorphism is $439-537^{\circ}C$ under pressure of 4.6-7.3 kb and its peak temperature and pressure are considered to reach to the range of 492-537 and 5.2-7.3 kb. And the temperature range of contact metamorphism occurred by intrusion of cretaceous granitic body, is $588-739^{\circ}C$ under pressure of 2.6-5.2 kb and its peak temperature and pressure are estimated as having the range of $697-739^{\circ}C$ and 3.8-5.2 kb that this amphibolites are estimated to pass through the metamorphic evolution of both the rise of temperature and the drop of pressure.

• Proceedings of the Mineralogical Society of Korea Conference
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• 2002.05a
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• pp.1-3
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• 2002

The eastward extension of the suture zone between the Sino-Korea and Yangtze cratons in the Korean Peninsula and Japanese islands remains debatable (Hiroi, 1981; Cluzel et al., 1991; Yin and Nie, 1993; Sohma and Kunugiza, 1993; Isozaki, 1997; Arakawa et at., 2000), and is related to our understanding of the continent-continent collision orogeny. The collision orogeny varies in tectono-metamorphic processes and the timing differs from place to place, as exemplified by the absence of coesite and micro-diamond in the Korean Peninsula and Japanese islands, because it is a long-lived process of more than several tens of million years from subduction to exhumation in the Wilson cycle, and because the suture zone extends more than several thousand kilometers with a curved shape from the Qinling area of China to the Hida highland area of Japan. Hiroi (1981) is the first paper to correlate the Unazuki metamorphic rocks of the Hida metamorphic belt in Japan with the Ogcheon belt in the Korean Peninsula based on the presence of 240 Ma medium P/T metamorphic rocks in both belts, but there is a lack of recent studies on this correlation. To resolve the correlationship, there are two approaches: 1) petrological studies characterizing the origin and P-T history of rocks and 2) in-situ micro-dating of fine-grained, zoned minerals of zircon, monazite, uraninite and thorite using the EPMA (U-Th-Pb chemical dating or CHIME depending on calibration method) and the SHRIMP (Sensitive High-resolution ion Microprobe) to decipher the timing of geological events. As a first step of these approaches, micro-dating was undertaken to rocks of the Hida metamorphic belt and its Mesozoic cover (Tetori Group) in the Hida highland area, central Japan.

• The Journal of the Petrological Society of Korea
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• v.17 no.4
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• pp.191-205
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• 2008

In order to use the geologic information data such as industrialization of rock resources, site enlargement and development planning, distributive ratios of rock types and geologic ages were obtained by the ArcGIS 9.2 program, and digital geologic and geographic maps of 1:250,000 scale, in the Chungbug, Chungnam and Daejeon areas, respectively. In the Chungbug area, 64 rock kinds are developed and their geologic ages can be classified into 8 large groups. In the geologic ages, the ratios are decreasing in the order of Jurassic, Precambrian, Age-unknown, Cretaceous, Quaternary, Cambro-Ordovician and Carboniferous-Triassic ages, all of which comprise most ratios of 98.48% in the area. In the rock types, the ratios show the decreasing order of Jurassic Daebo granite, Precambrian banded gneiss of Gyeonggi metamorphic complex, Cretaceous biotite granite, Quaternary alluvium, Great limestone group, Lower phyllite zone and Meta-sandy rock zone of age-unknown Ogcheon group, Triassic Cheongsan granite, Precambrian granitic gneiss of Gyeonggi gneiss complex, Pebble bearing phyllite zone of age-unknown Ogcheon group and biotite gneiss of Sobaegsan metamorphic complex, all of which comprise the prevailing ratio of 84.27% in the area. In the Chungnam area, 35 rock types are developed and their geologic ages can be classified into 6 large groups. In the geologic ages, the ratios are decreasing in the order of Precambrian, Jurassic and Quaternary ages, which occupy the prevailing ratio of 87.55% in the area. In the rock types, the ratios show the decreasing order of Jurassic Daebo granite, Precambrian banded gneiss of Gyeonggi metamorphic complex, Quaternary alluvium, Precambrian granite and granitic gneiss of Gyeonggi gneiss complex, Cretaceous acidic dykes, Lower phyllite zone and Pebble bearing phyllite zone of age-unknown Ogcheon group and Quaternary reclaimed land, which occupy the ratios of 74.28% in the area. In the Daejeon area, 11 rock types are developed and their geologic ages can be classified into 5 large groups. In the ages, the ratios are decreasing in the order of Jurassic, Age-unknown and Quaternary, which occupy most ratios of 93.40% in the area. In the rock types, the ratios show the decreasing order of Jurassic Daebo granite, Quaternary alluvium and Lower phyllite zone and Pebble bearing phyllite zone of age-unknown Ogcheon group, which occupy the prevailing ratios of 91.09% in the area.

• Economic and Environmental Geology
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• v.13 no.3
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• pp.167-184
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• 1980

The granitic plutons associated with Ogcheon geosynclinal zone can be grouped into three different subzones; SE-Subzone for the migmatitic and schistose granites of the southeast margin, 101-181m.y. old; NW-Subzone for those of the northwest margin, 112-163m. y. old; and C-Subzone for those of central part of the zone, 63-183m.y. old. The intrusives in C-Subzone are further subdivided into the older, adamellite to granodiorite (148-183m.y. old) and the younger, perthitic granites (63-106m,y. old). The metallogenic distribution of South Korea suggests that, in the Ogcheon Zone, it is possible to delineate an elongated polymetallogenic province in the general orientation of the zone intimately related with the migmatite and plutonic zones mentioned. Moreover, the mineralization in the province was basically controlled by the patterns of local geology involving country rocks and related igneous bodies, that permit subdivision of the province into the following three parts: Northeast (NE) Province consists dominantly of thick Paleozoic calcareous sediments; Middle (M) Province is characterized by predominant argillaceous and partly calcareous sediments of Precambrian to Late Paleozoic age; and Southwest (SW) Province consisting mainly of volcanic and arenaceous sediments of Mesozoic age. The three different plutonic zones with three different country rock provinces above mentioned make a combination which consists of nine classes. Each class can be assumed to be characterized by specific mineralization type. In order to classify the mineralization types, the present study sampled twenty six ore deposits and mineralized areas in Ogcheon zone as shown figure 2; eight ore deposits from plutonic SE-Subzone, ten from the plutonic NE-Subzone and eight from the plutonic C-Subzone. The characteristics of the classes are as follows: NE-SE is predominant in Au-Ag vein and Sn-migmatite of katazonal occurrence; NE-C is most productive in Pb-Zn and remarkable in Fe contact deposit in mesozone and partly Pb-Zn-Cu skarn in limestone and subordinate in mesozone and partly Pb-Zn pipes; M-SE is considerable in Au-Ag vein and rare elements (Nb, Ta, etc.) of pegmatite; M-C is predominant in F-veins in epizone and Mo-W, Fe, Cu veins occur in replacement type; M-NW is productive in Fe metamorphic and skarn types, partly remarkable in Cu, Pb-Zn contact; SW-SE is barren in mineralization related to Jurassic igneous rocks; SW-C is predominant in alunite and pyrophyllite in tuffs; and SW-NW is scarece in Pb-Zn, Cu, As and Au-Ag veins.

• The Journal of the Petrological Society of Korea
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• v.6 no.3
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• pp.151-165
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• 1997

The Kyemyeongsan area of Chungju in the NE part of the Ogcheon metamorphic zone, Koera, consists mainly of the Ogcheon Supergroup(Taehyangsan Quartzite, Hyangsanri Dolomite and Kyemyeogsan Formation) and the MeSozoic Chungju granite. The Kyemyeongsan Formation is composed mainly of metamorphic rocks of various grades derived from conglomeratic, basic, acidic, pelitic and psammitic rocks. The basic and acidic rocks show alternated or interfingered appearence, indicating that they were derived form bimodal type of magmatism in rift environment. Conglomeratic rocks overlie acidic volcanic rocks in geneal, but are underlain by both acidic plutonic and volcanic rocks. This indicaties that the acidic magmatism before the formation of conglomeratic rocks was different from that during or after the formation of conglomeratic rocks in its occurrence mode. The geological structure of the Ogcheon metamorphic zone in the Kyemyeongsan area, Chungju was formed at least by three phases of deormation. The first phase deformation(D1) formed a regional-scale sheath-type fold(F1) closed into the east. Its axial phane(S1) strikes NNW to NW and dips WSW to SW. The stetching lineation(L1), related to the sheath-type fold, plunges westward. The second phase deformation (D2) formed asymmetric fold(F2) of ESE-to SE-vergence with NNE to NE striking axial plane(S2) and $20~45^{\circ}/210~230^{\circ}$ plunging axis(L2). The F2 fold reoriented the original westward plunging L1 into northwestward plunging L1 in its lower limb(overturned limb). The third phase of deformation(D3) was recognized as chevron-type fold(F3) with $45^{\circ}/265$^{\circ}$ plunging axis. The F3 fold was formed by the compression of N-S direction, resulting in the reorientation of the original $20-45^{\circ}/210~230^{\circ}$ plunging L2 into mainly $35~45^{\circ}/260~280^{\circ}$ and subsidiarily $30~45^{\circ}/135~165^{\circ}$ plunging L2. After this deformation, open fold with NS striking and steeply E or W dipping axial plane is formed by the compression of E-W direction.