• Proceedings of the Mineralogical Society of Korea Conference
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• 2001.06a
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• pp.95-95
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• 2001

The Yeongdong basin is one of the pull-apart basins in the southwestern part of the Korean Peninsula that has developed during Cretaceous sinistal fault movement. The bimodal igneous activities (basalts and rhyolites) in the basin appear to be closely associated with the basin development. Here, we discuss the origin of the igneous rocks using chemical and radiogenic isotope data. Basaltic (48.4-52.7 wt% SiO$_2$) and rhyolitic (70.3-70.8 wt% SiO$_2$) rocks are slightly alkalic in a total alkali-silica diagram. The rhyolitic rocks with have unusually high K$_2$O contents (5.2-6.0 wt%). The basaltic rocks show an overall pattern of within-plate basalt in a MORB-normalized spider diagram, but have distinct negative anomaly of Nb, which indicates a significant amount of crustal component in the magma. The basaltic rocks plot within the calc-alkaline basalt field in the Hf/3-Th-Ta and Y/l5-La/10-Nb/8 discrimination diagrams. The eNd(T) values of the basaltic rocks (-13.6 to 14.3) are slightly higher than those of the rhyolitic rocks (-14.1 to 15.2), and the initial Sr isotopic ratios of the former (0.7085-0.7093) are much lower than those of the latter (0.7140-0.7149). However, the initial Nd and Sr isotope ratios of the igneous rocks in the Yeongdong basin are similar to those of the nearby Cretaceous igneous rocks in the Okcheon belt. The Pb isotope ratios plot within the field of Mesozoic granitoids outside of the Gyeongsang basin in Pb-Pb correlation diagrams. Since a basaltic magma requires the mantle source, the enriched isotopic signatures and negative Nb anomaly of the basaltic rocks suggest two possibilities for their origin: enriched mantle lithospheric source, or depleted mantle source with significant amount of crustal contamination. However, we prefer the first possibility since it would be difficult for a basaltic magma to maintain its bulk composition when it is significantly contaminated with granitic crustal material. The slightly more enriched isotopic signatures of rhyolitic rocks also suggest two possibilities: differentiate of the basaltlc magma with some crustal contamination, or direct partial melting of the lower crust. Much larger exposed volume of the rhyolitic rocks, compared with the basaltic rocks, indicates the latter possibility more favorable.

• The Journal of the Petrological Society of Korea
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• v.14 no.4 s.42
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• pp.226-236
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• 2005

Using the concept of granite suite/supersuite we hierarchically divided the Triassic granites in South Korea which have spatio-temporally close relationships each other. Among the Triassic granites in the Okcheon belt (western Yeongnam massif), the Baegrok granite and the Jeomchon granite can be grouped into one suite, the Baegrok suite, whereas the Cheongsan granite into the Cheongsan suite. These two suites can be grouped again into a larger supersuite, the Baegrok supersuite, on the basis of the similarity in the source rocks and the contrasts in the petrographic and geochemical characteristics. Three Triassic granites in the Gyeongsang basin - the Yeongdeok granite, the Yeonghae granite, and the Cheongsong granite - can be grouped into the Yeongdeok suite, Yeonghae suite and Cheongsong suite, respectively. These three suites can be grouped again into a larger supersuite, the Yeongdeok supersuite, on the basis of the similarity in the source rocks and the contrasts in the petrographic and geochemical characteristics. Nd-Sr isotopic signatures for the Baegrok supersuite are quite distinct from those for the Yeongdeok supersuite, indicating that the source materials of each granitic magma were not identical. The source rocks for the Baegrok supersuite are thought to be a mixture of two crustal components of the Yeongnam massif, whereas those for the Yeongdeok supersuite to be a mixture of the depleted mantle with the crustal components of the Yeongnam massif. The fact that the two contemporaneous granite supersuites were derived from the different sources can be explained by the difference of the tectonic environments where the granitic magmas were produced.

• Journal of the Korean earth science society
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• v.30 no.4
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• pp.427-443
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• 2009

Cretaceous intrusive and extrusive rocks in the southwestern part of the Yeongnam Massif are possibly the result of intensive magmatism which occurred in response to subduction of the Pacific plate beneath the northeast portion of the Eurasian plate. Geochemical and petrological study on the granitic rocks were carried out in order to constrain the petrogenesis of the granitic magma and to establish the paleotectonic environment of the area. Whole rock chemical data of the granitic rocks from the study area indicate that all the rocks have characteristics of calc-alkaline series in the subalkaline field. The overall geochemical features show systematic variations in each granitic body, but the source materials of each granitic body are thought to have been different in their chemical composition. The granodiorites distributed around Donggyori in the Bognae area (DGd) are different from other granitic rocks within the study area in the contents and differentiation trends of $Al_2O_3$ and MgO as well as in the contents of the trace elements such as Ba, Sr, Pb, Ni, Cr and Y DGd have geochemical features similar to slab-derived adakites such as high $Al_2O_3$, Sr contents and high Sr/Y, La/Yb ratios, but low Y and Yb contents. The major and trace element contents of the DGd fall well within the adakitic field, whereas other Cretaceous granites in the study area are plotted in the island arc ADR area in Sr/Y vs. Y diagram. On the ANK vs. A/CNK and tectonic discrimination diagrams, parental magma type of the granites corresponds to I-type and volcanic arc granite (VAG). Interpretations of the chemical characteristics of the granitic rocks favor their emplacement in a compressional tectonic regime at continental margin during the subduction of Pacific plate. The geochemical and tectonic features reveal that adakite-like signatures of the DGd were generated by the interaction of mantle peridotite and subducted slab-derived adakitic melts (caused by the thermal effect of ridge subduction), and which slightly modified by crustal contamination during emplacement.

• Economic and Environmental Geology
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• v.46 no.5
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• pp.391-409
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• 2013

The Hongseong area of the southwestern Gyeonggi massif is considered to be part of suture zone that is tectonically correlated with the Qinling-Dabie-Sulu belt of China in terms of the preservation of collisional evidences during Triassic in age. The Wolhyeonri complex, preserved at the center of the Hongseong area, consists mainly of Neoproterozoic orthogneisses and Middle Paleozoic intermediate- to high-grade metamorphic schists, orthogneisses and mafic metavolcanics. The area includes various Middle to Late Triassic intrusives (e.g. dyke or stock). They are mainly monzonite and aplite with small intrusions of monzodiorit, syenite and diorite in composition. The SHRIMP U-Pb zircon ages yield 237 Ma to 222 Ma. The geochemistry of the studied Triassic intrusives show similar subuction- or arc-type signatures having Ta-Nb troughs, depletion of P and Ti, and enrichment of LILEs (large ion lithophile elements). In addition, the Triassic plutons in the Hongseong area, including those from this study, mostly possess high-K calc-alkaline to shoshonitic tectonic affinity. These results could be tectonically correlated to the post-collisional magmatic event following the Triassic collision between the North and South China blocks in China. Therefore, the Triassic plutons in the Hongseong area offer an important insight into the Triassic geodynamic history of the NE Asian region.

• Economic and Environmental Geology
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• v.42 no.6
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• pp.541-548
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• 2009

The Dongrae thermal water area located at the southeastern marginal part of the Korean Peninsula is one of the oldest hot springs in Korea. The Dongrae thermal water shows Na-Cl type of water chemistry, whereas the shallow cold groundwater is Ca(-Na)-$HCO_3$ type. In this paper, we discuss the age of the Dongrae hot spring, i.e. groundwater cycle among meteoric water-surface water-shallow groundwater-hot spring water. The $^{87}Sr/^{86}Sr$ ratios of the thermal water in Dongrae area range from 0.705663 to 0.705688 and are lower than those of groundwater, surface water and rain water as well as aquifer bearing granite. These Sr isotopic signatures in the Dongrae thermal water indicate that the circulation rate between thermal water and current meteoric water including groundwater, surface water and rain water in the Dongrae area should be very slow. The $^{14}C$ age of the Dongrae hot spring water range from $1,271{\pm}36$ BP(before present) to $2,467{\pm}36$ BP whereas that of the shallow groundwater is $-495{\pm}33$ BP. This suggests that the period of groundwater cycle among meteoric water, surface water, shallow groundwater and hot spring should be more than 1,270 years. Then, it also indicates that the present Dongrae hot spring may be a mixed water between the old thermal water heated for at least 1,270 years and the present shallow cold groundwater.

• The Journal of the Petrological Society of Korea
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• v.20 no.4
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• pp.191-206
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• 2011

The emplacement ages, whole-rock geochemistry and Sr-Nd isotopic compositions of granitoid rocks from Cheongju area, South Korea, were investigated for delineating their petrogenetic link to the Jurassic Daebo granitoid rocks. Zircon crystals were collected from the diorite, biotite granite and acidic dyke samples in a single outcrop. Cross-cutting relationships show that the emplacement of diorite was postdated by the intrusion of biotite granite. Both rocks have been subsequently intruded by acidic dyke. The U-Pb isotopic compositions of zircon from the diorite, biotite granite, and acidic dyke were measured using a SHRIMP-II ion microprobe, yielding the crystallization ages of $174{\pm}2Ma$, $170{\pm}2Ma$, and $170{\pm}5Ma$, respectively, with 95% confidence limits ($t{\sigma}$). The emplacement ages are consistent with those determined from the above relative ages. The major and trace element patterns of the rocks are consistent with those of the Jurassic Daebo granitoid rocks, possibly suggesting a subduction-related I-type granite. The geochemical signature is, however, betrayed by the Sr and Nd isotopic compositions of these rocks. The isotopic signatures suggest that the rocks were produced either by the partial melting of lower-crust or by the mantle-derived magma contaminated by the basement rocks during its ascent and/or emplacement. In addition, the inherited ages of zircons of the rocks (ca. 2.1, 1.8, 0.8 and 0.4 Ga) suggest a possible assimilation with crustal rocks from the Gyeonggi massif and Ogcheon metamorphic belt.

• 한국해양학회지
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• v.23 no.3
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• pp.110-122
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• 1988

Between the Clarion and Clipperton fracture zones of the Northeastern Pacific, nodules and crusts were collected from abyssal plain and hills by the Korea Ocean Research and Development Institute in December, 1983 aboard the R/V KANA KEOKI of the Hawaii Institute of Geophysics. Mineralogical and geochemical data of bulk nodules are obtained and compared with analyses of other studies. Mechanisms of nodule formation are discussed based on these data. Generally, the nodules of the KONOD-1 site are composed of todorokite and ${\delta}-MnO_2$. The contents of Mn, Fe, Ni, and Cu of the bulk nodules are variable and the average contents of metals are slightly lower (Mn, 21.40%; Ni, 0.9%; Cu, 0.8%) than those of nodules from other abyssal plains between the Clarion and Clipperton fracture zones. High Mn/Fe (average 3.9; maximum 5.9) and Cu/Ni (average 0.8; maximum 1.0) ratios are similar to the nodules that were formed diagenetically in the northeast Pacific. The chemical characteristics of the KONOD-1 nodules reflect their sedimentary environments; nodules with higher diagenetic signatures occur in areas of thin Quaternary siliceous ooze, and nodules of lower diagenetic influence occur in topographically irregular abyssal hill areas.

• The Journal of Engineering Geology
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• v.25 no.4
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• pp.533-545
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• 2015

Spatial and seasonal variations in hydrogeochemical characteristics and the factors affecting the deterioration in quality of shallow portable groundwater in an agricultural area are examined. The aquifer consists of (from the surface to depth) agricultural soil, weathered soil, weathered rock, and bedrock. The geochemical signatures of the shallow groundwater are mostly affected by the NO₃⁻ and Cl⁻ contaminants that show a gradual downward increase in concentration from the upper area, due to the irregular distribution of contamination sources. The concentrations of the major cations do not varied with the elapsed time and the NO₃⁻ and Cl⁻ ions, when compared with concentrations in background groundwater, increase gradually with the distance from the upper area. This result suggests that the water quality in shallow groundwater deteriorates due to contaminant sources at the surface. The contaminations of the major contaminants in groundwater show a positive linear relationship with electrical conductivity, indicating the deterioration in water quality is related to the effects of the contaminants. The relationships between contaminant concentrations, as inferred from the ternary plots, show the contaminant concentrations in organic fertilizer are positively related to concentrations of NO₃⁻, Cl⁻, and SO₄²⁻ ions in the shallow portable groundwaters, which means the fertilizer is the main contaminant source. The results also show that the deterioration in shallow groundwater quality is caused mainly by NO₃⁻ and Cl⁻ derived from organic fertilizer with additional SO₄²⁻ contaminant from livestock wastes. Even though the concentrations of the contaminants within the shallow groundwaters and the contaminant sources are largely variable, it is useful to consider the ratio of contaminant concentrations and the relationship between contaminants in groundwater samples and in the contaminant source when analyzing deterioration in water quality.

• Economic and Environmental Geology
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• v.56 no.3
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• pp.239-257
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• 2023

Sangdong deposit, a W-Mo skarn deposit, is located in Taebaeksan mineralized district, hosting vertically developed scheelite-quartz veins that formed at the late ore-forming stage. In this study, we tried to examine the geochemical signatures of ore-forming fluids and vein-forming mechanisms by analyzing the micro-texture of quartz veins and trace element concentrations of quartz. As a result of texture analyses, quartz veins in the hanging wall orebody and the foot wall orebody commonly exhibit the blocky and the elongate blocky texture, respectively, whereas quartz veins in the main orebody show both textures. These textural differences indicate that quartz veins from the hanging wall orebody were precipitated by the primary hydrofracturing due to H₂O saturation in the igneous body with relatively high temperature and pressure at a vein-skarn stage, and after that, repeated hydrofracturing caused the formation of quartz veins from the main orebody and foot wall orebody. The results of trace element concentrations show that Li⁺+Al³⁺↔Si⁴⁺ is a main substitution mechanism. However, those of the foot wall orebody were clearly divided into a Li⁺-dominated substitution and a Na⁺-, K⁺-dominated substitution. Considering that quartz veins from the foot wall orebody commonly show the elongate blocky texture, such a distinction means that it is a result of repeated injections of fluid with the different composition. Ti concentrations of quartz from the hanging wall, main, and the foot wall orebody are 28.6, 8.2, and 15.7 ppm in average, respectively. Given a proportional relationship between the precipitation temperature and Ti concentrations, it seems that quartz veins from the hanging wall orebody were precipitated at the highest temperature. Al concentrations of the hanging wall, main, and the foot wall orebody having an inverse relationship with fluid pH are 162.3, 114.2, and 182.5 ppm in average, respectively. These results show that Al concentrations in vein-forming fluids were not changed dramatically. Moreover, these concentrations are extremely low in comparison with the other hydrothermal deposits. This indicates that quartz in overall ore veins at Sangdong deposit was precipitated from the constant condition with slightly acidic to near neutral pH.