• Economic and Environmental Geology
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• v.26 no.4
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• pp.499-505
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• 1993

The Imgye hornblendites occur as intrusive sills or dykes within the mylonite zone developed along the contact boundary between Precambrian Jungbongsan granite and Cambrian Jangsan quartzite or Myobong slate formations. The hornlendites belong to the subalkaline and tholeiitic series. In tectonomagmatic discrimination diagrams such as $TiO_2-K_2O-P_2O_5$, 2Nb-Zr/4-Y and $TiO_2-10MnO-10P_2O_5$, the hornblendites are classified into continental- and island-arc tholeiites. The hornblendites show fractionated REE patterns with $(La/Yb)_{CN}$ ranging from 3.73-4.56. In incompatible element abundance variations, the hornblendites show distinctive positive and negative anomalies for Rb and Nb, respectively, and unfractionated patterns of immobile incompatible elements such as Y and Yb. The REE patterns of the hornblendites are also similar to those of typical continental back-arc tholeiites and those of the Precambrian Okbang amphibolites in the Socheon-meon, Bonghwa-gun. Accoiding to geochemical characteristics above-mentioned, the hornblendites seem to have been formed from tholeiitic magmas of depleted upper mantle source, contaminated by crustal material en route to continental back-arc basin.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.12a
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• pp.73-83
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• 2007

We interpreted marine seismic profiles in conjunction with swath bathymetric and magnetic data to investigate rifting to breakup processes at the eastern Korean margin that led to the separation of the southwestern Japan Arc. Analysis of rift fault patterns suggests that rifting at the Korean margin was primarily controlled by normal faulting resulting from extension rather than strike-slip deformation. Two extension directions of E-W and NW-SE for rifting are recognized. We interpret that the E-W direction represents initial rifting at the inner margin and the NW-SE direction probably represents the extension in response to tensional tectonics associated with the subduction of the Pacific Plate in the NW direction. No significant volcanism was involved in rifting. In contrast, the inception of sea floor spreading documents a pronounced volcanic phase which appears to reflect asthenospheric upwelling as well as rift-induced convection particularly in the narrow southern margin. We suggest that structural and igneous evolution of the Korean margin, although it is in a back-arc setting, can be explained by the processes occurring at the passive continental margin with magmatism influenced by asthenospheric upwelling.

• The Journal of Engineering Geology
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• v.19 no.4
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• pp.459-474
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• 2009

By the analysis of discontinuity at the outcrop and lineament on the satellite image, the joints have deeply relationship with the lineaments. The joint spaces at the drilling core are mostly 1~20 cm but at the rhyolite which is distributed near fault they have more closely. These volcanic rocks belong to the subalkaline series tuff, rhyolite, basalt in the study area from the diagram of $Nb/Y-Zr/TiO_2$. The composition diagram of Hf/3-Th-Nb/16 show destructive plate-margin basalt and their differentiates. The environment of formation of volcanics are normal continental arc. Most of LREE show high enriched pattern but HREE show depleted pattern. The K/Ar age of intermediate volcanics, tuff, rhyolite, crystal tuff are 55.3Ma, 77.25 Ma~91.22Ma, 63.16~64.39Ma, 54.49 Ma respectively.

• The Korean Journal of Petroleum Geology
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• v.13 no.1
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• pp.17-23
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• 2007

Gravity characteristics are investigated in the vicinity of the DASAN scientific station, located at the Svalbard Archipelago, the Arctic using ArcGP data. Boundary effects of free-air gravity anomalies, which appeared generally at the continental margin, are erased after Bouguer correction was applied. Complete Bouguer anomalies produced after terrain correction by GrOPO30 show that gravity anomalies increase from continent to marine. This phenomena seem to be related to the rise of Moho discontinuity. The cut-off frequency of 0.16 was decided after power spectrum analysis and the gravity anomalies were divided into two parts. Residual anomalies in high frequency part show that characteristics of high values along the faults and of low values related to thick sediments in the continent. Characteristic is low values from basement subsidence of continental slope or thick sediments in the marine. The undulation of Moho discontinuity from 3-D inversion modeling show typical characteristics of continental margin that become higher from Svalbard archipelago to Knipovich ridge bordering Eurasian plate.

• Journal of the Korean Geophysical Society
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• v.9 no.3
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• pp.189-197
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• 2006

The Korea Plateau is a continental fragment rifted and partially segmented from the Korean Peninsulaat the initial stage of the opening of the East Sea (Japan Sea). We interpreted marine seismic profiles from the South Korea Plateau in conjunction with swath bathymetric to investigate processes of con-tjnental rifting and separation of the southwestern Japan Arc. The SouU-i Korea Plateau preserves funda-mental elements of rift architecture comprising a seaward succession of a rift basin and an uplifted rift flank passing into the slope, typical of a passive continental margin. Two distinguished rift basins (Onnuri and Bandal Basins) in the South Korea Plateau are bounded by major synthetic and smaller antithetic faults, creating wide and symmetric profiles. The large-offset border fault zones of these basins have convex dip slopes and demonstrate a zig-zag arrangement along strike. Rifting was primarily controlled by normal faulting resulting from extension orthogonal to the inferred line of breakup along the base ofthe slope rather U-ian strike-slip deformation. Two extension direcdons for rifdng are recog-nized; U-ie Onnuri Basin was rifted in U-ie EW direction; U-ie Bandal Basin in U-ie EW and NW-SE directions, suggesting two rift stages. We interpret that the E-W direction represents initial rifting at the inner margin; while the Japan Basin widened, rifting propagated repeatedly from the Japan Basin to the southeast toward the Korean margin but could not penetrate the strong continental lithosphere of the Korean Shield and changed direction to the south, resulting in E-W extension to create the rift basins at the Korean margin. The Hupo Basin to the south of the Korea Plateau is estimated to have formed in this process. The NW-SE direction probably represents the direction of rifting orthogonal to the inferred line of breakup along the base of the slope of the South Korea Plateau; after breakup the southwestern Japan Arc separated in the SE direction, indicating a response to tensional tectonics associated with the subduction of the Pacific Plate in the NE direction. We suggest that structural evolution of the eastern Korean margin can be explained by the processes occurring at the passive continental margin.

• Economic and Environmental Geology
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• v.22 no.2
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• pp.141-150
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• 1989

In order to make economic and geological evaluation of coal in Korea, proximate and ultimate analyses were carried out as well as coal petrological studies such as maceral analyses, vitrinite reflectance and sporinite fluorescence measurement. The coeffcient of correlation between each factor of both conventional utilization and coal petrological parameters were studied as in Table 5 and 6. Their conclusions were as follow: (1) for anthracite, the good parameters of coal rank are mean vitrinite reflectance, carbon content, hydrogen content and H/C atomic ratio: (2) for brown coal and sub-bituminous coal, the good parameters of coal rank are carbon content, calorific value, moisture content, hydrogen content, oxygen content and O/C atomic ratio as well as vitrinite reflectance and sporinite fluorescence. An attempt is made to infer the coalforming environment by utilization of coal petrological analyses and to make comparison of coal analyses with proximate and ultimate analyses throughout the island arc region including Japan, Philippine and Indonesia and continental region including USA, Canada and Australia. As a result, meceral composition of Paleozoic and Mesozoic anthracite are similar to that of the Paleozoic continental coals, which were formed under dry conditions or low water table, but the coalification degree suddenly increased during Daebo orogeny (middle Jurassic to lower Cretaceous). The Tertiary coal resembles those of Tertiary island arc region coal characterized by higher calorific value, volatile matter content and H/C atomic ratio and by the formation of coal under wet conditions or higher water table.

• Economic and Environmental Geology
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• v.26 no.4
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• pp.489-498
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• 1993

The Okbang amphibolites occurring as sill-shaped bodies within the Precambrian Wonnam Group have been studied in terms of geochemical characteristics for their tectonomagmatic environments. The amphibolites fall in the ortho-amphibolite fields in Ni and Cr versus Cu diagrams. They belong to subalkaline and tholeiitic series in total alkali versus silica and ternary AFM diagrams, respectively. They show the compositional variation corresponding to the differentiation trend of tholeiitic suites. In discrimination diagrams using high-field-strength elements such as Ti, Zr, Nb and Y, the amphibolites show geochemical affinities to both of volcanic-arc tholeiites and normal (depleted) mid-oceanic ridge tholeiites. The REE patterns of the amphibolites are nearly flat and extremely similar to those of back-arc tholeiites. $(La/Yb)_{CN}$ ratios vary from 0.89 to 2.02 with an average value of 1.23. Such low light-REE abundances in the amphibolites suggest that they were derived from the upper mantle source depleted in these elements. In view of geochemical characteristics showing strong enrichments of incompatible elements such as K and Rb, distinctive negative Nb anomalies, depletions of light-REE observed also in normal (depleted) mid-oceanic ridge tholeiites, and unfractionated immobile elements such as Y and Yb, the tholeiitic magmas, from which the parent rocks of the amphibolites were formed, would be generated from a depleted upper mantle source and contaminated by continental crustal materials en route to surface. Tectonomagmatic environment for the amphibolites can be assumed to be continental back-arc basin.

• Proceedings of the KSRS Conference
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• 1999.11a
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• pp.13-18
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• 1999

Land cover map of 30 arc-second grid by NOAA AVHRR data for the whole Asia was produced by the authors as the project of the Asian Association on Remote Sensing(AARS). Land cover change monitoring of continental scale by satellite data needs preprocessing to remove undesirable factors due to noises, atmosphere, or the effect by solar zenith angle. The paper describes the method to remove these factors. The most important thing for better mapping/monitoring in the future is the accumulation of ground truth data by many land cover related researchers. The project of the development of Global Land Cover Ground Truth Database(GLCGT-DB) is proposed.

• The Journal of the Petrological Society of Korea
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• v.18 no.2
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• pp.93-114
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• 2009

Lithological and petrochemical characteristics and tectonic setting of the Cretaceous volcanic rocks in Hampyeong area located in the southwestern part of Okchon Zone, were studied by field survey and petrochemistry of major, trace, and rare earth elements. The $SiO_2$contents of the volcanic rocks range from 50.8 to 77.2wt.%. With increasing $SiO_2$, $Al_2O_3$, $Fe_2O_3\;^T$, $TiO_2$, MnO, CaO and MgO contents decrease and $K_2O$content increase, but $Na_2O$content is scatter to the trend. According to TAS and AFM diagrams, the Cretaceous volcanic rocks are calc-alkaline series. On the discrimination diagram of $K_2O$versus $SiO_2$, the volcanic rocks belong to high-K rocks series. The trace element compositions and REE patterns of the volcanic rocks, characterized by a high LILE/HFSE ratio and enrichments in LREE, indicate that they are typical of continental margin arc calc-alkaline volcanic rocks associated with the subduction environment. The ratios of Ba/Ta and Ba/La indicate that they are associated with volcanic arc-related magmatism. The Cretaceous volcanic rocks in Hampyeong area might be located in the Eurasian continental margin, related to the Pacific type tectonic environment during the Cretaceous times.

• The Journal of the Petrological Society of Korea
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• v.19 no.1
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• pp.67-87
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• 2010

This article deal with petrotectonic setting and petrogenesis from petrography and chemical analyses of the Cretaceous volcanic and intrusive rocks in the Cheolwon basin. The volcanic rocks are composed of basalts in Gungpyeong Formation, Geumhaksan Andesite, and rhyolitic rocks (Dongmakgol Tuff, Rhyolite and Jijangbong Tuff), and intrusive rocks, Bojangsan Andesite, granite porphyry and dikes. According to petrochemistry, these rocks represent medium-K to high-K basalt, andesite and rhyolite series that belong to calc-alkaline series, and generally show linear compositional variations of major and trace elements with increase in $SiO_2$ contents, on many Harker diagrams. The incompatible and rare earth elements are characterized by high enrichments than MORB, and gradually high LREE/HREE fractionation and sharp Eu negative anomaly with late strata, on spider diagram and REE pattern. Some trace elements exhibit a continental arc of various volcanic arcs or orogenic suites among destructive plate margins on tectonic discriminant diagrams. These petrochemical data suggest that the basalts may have originated from basaltic calc-alkaline magma of continental arc that produced from a partial melt of upper mantle by supplying some aqueous fluids from a oceanic crust slab under the subduction environment. The andesites and rhyolites may have been evolved from the basaltic magma with fractional crystallization with contamination of some crustal materials. Each volcanic rock may have been respectively erupted from the chamber that differentiated magmas rose sequentially into shallower levels equivalenced at their densities.