• Economic and Environmental Geology
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• v.42 no.3
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• pp.247-259
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• 2009

This study is focused on the relationship between whole rock boron contents and metamorphic P-T conditions of metasedimentary rocks from northeastern Yeongnam massif around Samcheok area, Korea. Metamorphic P-T conditions of sillimanite and garnet zones based on the Ti-biotite geothermometer is 553-687$^{\circ}C$ and 582-722$^{\circ}C$ at 4-6 kbar, respectively. In the metasedimentary rocks, boron contents in whole rock decrease with increasing metamorphic grade, from sillimanite zone (9.60-189 ppm B) to garnet zone (2.63-15.97 ppm B), except one sample (90.9 ppm B) from garnet zone containing graphites. Boron depletion in garnet zone has relation with mode of tourmaline which are broken down with increasing metamorphic temperature. Boron contents are indirectly proportional to major and trace elements such as $Al_2O_3$, MgO, $Fe_2O_3$, $K_2O$, Li, Ba, Sc, Co, Cr, Rb and Cs that are abundant in tourmalines. In conclustion, tourmalines and graphite are modulator of boron contents in metasedimentary rocks. In the biotite granitic gneisses, boron contents (2.62-12.2 ppm B) are similar or lower than those of metasedimentary rocks and have no relation with metamorphic P-T conditions.

• The Journal of the Petrological Society of Korea
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• v.17 no.1
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• pp.16-35
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• 2008

We study metamorphism of metasedimetary rocks and origin and evolution of leucogranite form Samcheok area, northeastern Yeongnam massif, South Korea. Metamorphic rocks in this area are composed of metasedimentary migmatite, biotite granitic gneiss and leucogranite. Metasedimentary rocks, which refer to major element feature of siliclastic sediment, are divided into two metamorphic zones based on mineral assemblages, garnet and sillimanite zones. According to petrogenetic grid of mineral assemblages, metamorhpic P-T conditions are $740{\sim}800^{\circ}C$ at $4.8{\sim}5.8\;kbar$ in the garnet zone and $640-760^{\circ}C$ at 2.5-4.5kbar in sillimanite zone. The leucogranite (Imwon leucogranite) is peraluminous granite which has high alumina index (A/CNK=1.31-1.93) and positive discriminant factor value (DF > 0). Thus, leucogranite is S-type granite generated from metasedimentary rocks. Major and trace element diagram ($R_1-R_2$ diagram and Rb vs. Y+Nb etc.) show collisional environment such as syn-collisional or volcanic arc granite. Because Rb/sr ratio (1.8-22.9) of leucogranites is higher than Sr/Ba ratio (0.21-0.79), leucogranite would be derived from muscovite dehydrate melting in metasedimentary rocks. Leucogranites have lower concentration of LREE and Eu and similar that of HREE relative to metasedimentary rocks. To examine difference of REEs between leucogranites and metasedimentary rocks, we perform modeling using volume percentage of a leucogranite and a metasedimenatry rock from study area and REE data of minerals from rhyolite (Nash and Crecraft, 1985) and melanosome of migmatite (Bea et al., 1994). Resultants of modeling indicate that LREE and HREE are controlled by monazites and garnet, respectively, although zircon is estimated HREE dominant in some leucogranite without garnet. Because there are many inclusions of accessary phases such as monazite and zircon in biotites from metasedimentary rocks. leucogranitic magma was mainly derived from muscovite-breakdown in metasedimenary rocks. Leucogranites can be subdivided into two types in compliance with Eu anomaly of chondrite nomalized REE pattern; the one of negative Eu anomaly is type I and the other is type II. Leucogranites have lower Eu concetnrations than that of metasedimenary rocks and similar that of both type. REE modeling suggest that this difference of Eu value is due to that of components of feldspars in both leucogranite and metasedimentary rock. The tendency of major ($K_2O$ and $Na_2O$) and face elements (Eu, Rb, Sr and Ba) of leucogranites also indicate that source magma of these two types was developed by anatexis experienced strong fractionation of alkali-feldspar. Conclusionally, leucogranites in this area are products of melts which was generated by muscovite-breakdown of metasedimenary rock in environment of continetal collision during high temperature/pressure metamorphism and then was fractionated and crystallized after extraction from source rock.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.09a
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• pp.369-372
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• 2004

This study presents the hydrogeochmical investigation to know the effect of geology and sources for water quality in small potable water supply system at rural area. The results of water quality in Geumsan area showed the 3.2% of water samples exceeded the limit of drinking water standard by bacteria. The hydrochemical investigation results indicated the high EC, Ca and HCO$_3$ in surface water and metasedimentary rocks and this is caused by the dissolution of calc-slicate minerals of metasedimentary rocks.

• Proceedings of the Mineralogical Society of Korea Conference
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• 2003.05a
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• pp.54-54
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• 2003

The metasedimentary rocks together with various granitoids are the main constituents in Taebaeksan gneiss complex, northern Yeongnam Massif. Chemical compositions of sedimentary rocks may reflect the nature of the provenance and could be crucial for understanding the evolution of early continental crust. Previous workers have suggested that the provenance and tectonic studies based on the geochemistry of sediments are applicable to the Precambrian samples. In this study we analyzed the major, trace and REE elements of metasedimentary rocks to understand their provenance and tectonic setting during sedimentation. The overall geochemical characteristics of metasedimentary rocks are similar to those of average shale of the post-Archean. Major element chemistry indicates mature and sorted nature of the sediments. The degree of weathering in the source rocks the is not uniform, as inferred from a large scatter in chemical indices of weathering (CIW). The immobile trace elements such as Th, Sc, and REE can be used to discriminate various sedimentary processes. The Th/sc ratios (0.9 - 4.4) are larger than those of the upper crust and average shale, suggesting that the felsic source predominates. The contents of Ni and Cr and the variations in the ratio of compatible to incompatible elements are similar to the average post-Archean shale. Uniform chondrite-normalized REE pattern with the LREE enrichment (LaN/SmN = 4.9 ${\pm}$ 0.4) and slight negative Eu anomalies (Eu/Eu$\^$*/ = 0.7 ${\pm}$ 0.1) also support this observation. The presence of negative Eu anomaly indicates that intracrustal igneous processes involving plagioclase separation have affected the provenance rocks. The LREE enrichment implies the major role of felsic rocks in source rocks. The eNd (1.9 Ga) values of metasediment rocks vary from 9.4 to 6.7, corresponding to TDM of 2.9 - 2.7 Ga. On the other hand, the 147Sm/144Nd ratios are 0.1079 - 0.1101, corresponding to typical tettigenous sediments. The geochemical features of metasedimentary rocks such as high abundances of large ion lithophile elements, high ratios of Th/Sc and La/Sm, commonly high Th/U ratios, negative Eu anomalies, and negative eNd, suggest a provenance consisting virtually entirely of recycled upper continental crust in passive margin environment. Tectonic discrimination diagrams based upon major element compositions also support this suggestion. In conjunction with igneous activity and metamorphism in the convergent margin setting at 1.8 - 1. 9 Ga, the transition from passive margin to active margin characterize the Paleoproterozoic crustal evolution in northern Yeongnam Massif.

• Economic and Environmental Geology
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• v.23 no.1
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• pp.35-57
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• 1990

This study has been carried out on the Pegmatites, Naedeogri Granites, Nonggeori Granites and Metasedimentary rocks in the middle area of Taebaeksan region to investigate the geochemical properties and possibility of productivity. Pegmatites are characterized by metamorphosed anatectic pegmatite and differentiated magmatic pegmatite, and are mixed type of rare-element pegmatite and mica-bearing pegmatite by the classification of Ginsburg(1979). The petrological type of the igneous rocks is thought to be calcalkali, subalkaline and peralumious. According to chemical variations against D. I., differentiation trends from Naedeogri and Nonggeori Granites through non-mineralized pegmatites to mineralized pegmatites are supposed. From the relationship between oxided and $SiO_2$, pegmatites and Nonggeori Granite have shown similar tendencies and bulk composition of pegmatites and similar to metasedimentary rocks near the intrusives. By judging the correlations of trace elements, it is elucidated that pegmatites adjacent to Naedeogri and Nonggeori Granites have been originated in magma differentiation from these granites and the others have been differentiated by remelting or partial melting from metasedimentary rocks. $Sp_5$, $Sp_8$, and $Sp_9$ pegmatites are considered as productive rocks, and $Sp_4$, $Sp_6$, $Sp_7$, $Sp_{10}$, $Sp_{11}$, and $Sp_{12}$ pegmatites and granites are supposed to have a weak productivity, in terms of element ratios related with Sn mineralizations. Tourmalines in productive pegmatites are formed under the circumstance of Li-poor granitoids and associated with pegmatites, and the others are seemed to be originated in metapelites and metapsammites which are not coexisting with an Al-saturating phase. Three types of chemical zoning are noticed in tourmalines: (1) apparently homogeneous compositional patterns, (2) a continuous core-to-rim zoning and, (3) a discontinuous core-to-rim zoning. From results of EPMA of tourmalines, Al, Mg and Ca increase closer to rim, while Fe decreases.

• Economic and Environmental Geology
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• v.24 no.3
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• pp.277-285
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• 1991

We applied Sm-Nd isotopic system to so-called amphibolites occurring within the Ogcheon group to provide constraints on the age of the metasedimentary rocks and to characterize tectonic environment of basaltic magmatism. An internal mineral isochron age of $677{\pm}91Ma({\sigma})$ was obtained from a coarse-grained, intrusive, amphibolite near Mungyeong. Considering previous studies on the age of the Ogcheon group, we interpret that the isochron represents either early metamorphic or emplacement age. The depositional age of the metasedimentary rocks intruded by the amphibolite would be prior to late Proterozoic. The present study and Cambro-Ordovician fossil evidences of previous workers suggest that both Precambrian and Phanerozoic rocks are present in the Ogcheon group. Positive ${\varepsilon}$ Nd values(+2.4 to +3.5) of four whole rocks indicate mantle origin for the amphibolite. These isotopic data, along with published immobile trace element data of Cluzel et al.(1989), strongly suggest that parental rocks of the amphibolite formed in an intraplate environment rather than in island arc or midocean ridge. The age and tectonic environment of amphibolites in the Ogcheon belt suggest that the basaltic magmatism may be related to the late Proterozoic break-up of a presumed supercontinent, but not to the Triassic(?) collision between North and South China continents.

• The Journal of the Petrological Society of Korea
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• v.22 no.4
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• pp.263-272
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• 2013

We investigated the lithology and petrography of granites and metasedimentary rocks in Deokjeok Island at the western margin of the Gyeonggi massif. The major lithology comprises the biotite granite that intrudes all other types of rocks. A minor amount of mylonitized porphyritic granite crops out along the southeastern coast. Metasedimentary rocks in the north are further divided into: (1) sheared quartzite-schist to the northeast; and (2) relatively less-deformed, low-grade metasedimentary rocks to the northwest. The former contains quartz grains showing undulatory extinction and subgrain aggregates as well as minor amount of primary chlorite and biotite in the muscovite-rich matrix. Metamorphic condition belongs to the greenschist facies or the biotite zone. On the other hand, the latter unit consists of meta-conglomerate, meta-sandstone, meta-pelite, and black slate. Regardless of the lithology, the intensity of deformation apparently increases eastward to develop the flow banding of quartz in the shear zone.

• Proceedings of the Petrological Society of Korea Conference
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• 2003.05a
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• pp.54-54
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• 2003

• The Journal of the Petrological Society of Korea
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• v.19 no.2
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• pp.157-165
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• 2010

The age unknown Ogcheon metasedimentary rocks and the Jurassic Ogcheon granite (Jocgr) intruding it are distributed in the Ogcheon area, which is located in the central part of the Ogcheon Belt, Korea, This paper newly examines the timing of Honam shearing on the basis of the microstructural researches on time-relationship between the crenulation of Ogcheon metasedimentary rocks and the contact metamorphism by the intrusion of Jocgr. The D2 crenulation phase, which is defined by the microfolding of the S1 foliation in the metasedimentary rocks, is divided into two sub-phases. The one is a sub-phase of Early crenulation (D2a) which is included within old andalusite porphyroblasts, and the other is that of Late crenulation (D2b) which warps around the old andalusite. But they show the same dextral shear sense, the axial planes parallel to each other, and a single crenulation at outcrop scale. The contact metamorphism of andalusite-sillimanite type by the Jocgr occurred during the inter-phases of D2a and D2b, and crystallized the old andalusite masking the D2a crenulation and fibrous sillimanites replacing the D2a crenulation-forming muscovites. New andalusite porphyroblasts synkinematically grew in pressure shadows around the old andalusite or in its outermost mantles during the early stage of the D2b. The D2b occurred still continuously after the growth of the andalusite ceased (= later stage of the D2b). It indicates that the D2b occurred continuously during the period when the Ogcheon granite was still hot and cool. From this study, the crenulation history of Ogcheon metasedimentary rocks and the timing of Honam shearing would be newly established and reviewed as follows. (1) Early Honam shearing; formative period of Early crenulation, (2) main magmatic period of Jurassic granitoids; growth of the old andalusite and fibrous sillimanite by the intrusion of Jocgr, (3) main cooling period of Jurassic granitoids; formative period of Late crenulation related to Late Honam shearing, growth of the new andalusite in the early stage of D2b. Thus, this study proposes that the Honam shear movement would occur two times at least before and after the intertectonic phase which corresponds to the main magmatic period of Jurassic granitoids.

• Journal of Soil and Groundwater Environment
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• v.12 no.5
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• pp.64-72
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• 2007

Nationwide occurrence of arsenic in groundwater of Korea was investigated with the data from the groundwater quality monitoring stations. During 2001-2006, As has been quantitatively detected in 3.0 % of the total wells $(5.0{\sim}188{\mu}g/L)$, and its geographical distribution suggests 3 groups: an urbanized and industrialized area (Seoul and its neighbouring province), and two naturally occurring areas (Chungbuk and Gyeongnam provinces). Natural occurrence of As appears to be geologically related with Ogcheon metasedimentary rocks and Cretaceous volcanic rocks. Based on the results of the previous studies in the high As sites, the oxidation of sulfides can be a major control on As concentrations in groundwater in the mineralized and altered zone within the area of Cretaceous volcanic rocks. Desorption process under slightly high pH conditions may also be responsible for high As in groundwater in areas of Ogcheon metasedimentary rocks.