• The Journal of the Petrological Society of Korea
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• v.14 no.1
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• pp.45-60
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• 2005

This study was intended to elucidate the petrography and geochemical characteristics of the Someori Basalt in the Udo monogenetic volcano, eastern Jeju Island. The Someori basalts consist of plagioclase, olivine, orthopyroxene, clinopyroxene and ilmenite. The Someori basalts are plotted into subalkali rock series on the TAS diagram, and belong to tholeiitic basalts in the diagram of alkali index against to Al₂O₃ contents. The basalts belong to tholeiitic rock series, having normative quartz (less than 3.9%) + hypersthene + diopside.

• Geosciences Journal
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• v.22 no.6
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• pp.955-973
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• 2018

Twenty-eight beach sand samples from the shorelines of Aegean islands adjacent to the plutonic rocks of the Atticocycladic zone were analyzed for major and rare earth element (REE) contents. Results are compared with the adjacent plutonic rocks, in order to determine relative enrichments or depletions and assess the potential for REE exploitation. Among the samples, several are significantly enriched in REE, being deposits of heavy minerals and their concentrations are controlled by the sea waves and local winds. These samples contain Th, U and REE rich minerals such as zircon, xenotime and allanite. The available geochemical characteristics were also used to confirm the parent rocks of the beach sands. The heavy fractions (total, total magnetic and total non-magnetic) of the beach sands are very well correlated with the Heavy REE (HREE) concentrations. Among the minerals of the heavy magnetic fraction, allanite seems to control the REE content in the heavy mineral-enriched samples, while from the heavy non-magnetic fraction, zircon controls mainly the HREE fraction. One site from Mykonos and 3 from Naxos could have potential for REE exploitation as they present the highest ${\Sigma}REE$ and HREE contents than other beach sand placers measured in Greece (Kavala, Sithonia, Maronia, Samothraki, NE Chalkidiki).

• Korean Journal of Mineralogy and Petrology
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• v.33 no.3
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• pp.165-173
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• 2020

The activity of living microorganism directly or indirectly affects to the biomineralization in sediments and rocks that display the unique biotic structure. Minerals in the biotic structures showed unique properties and bypass the thermodynamic and kinetic barriers. Therefore, investigations on the biotically induced microstructure is essential to identify the new mineral formation mechanism by analyzing crystal structures and morphology at a nano-scale. The significant implication as well as advantages of using scanning electron microscopy to characterize the biotic structures were discussed in this paper for the examples of hydrothermal vent area microbial mat and deep-sea ferromanganese crust sample.

• Korean Journal of Mineralogy and Petrology
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• v.33 no.3
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• pp.293-305
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• 2020

An eruption of Taal Volcano in the Philippines began on January 12, 2020. The Philippine Institute of Volcanology and Seismology (PHIVOLCS) subsequently issued an Alert Level 4, indicating that "a hazardous explosive eruption is possible within hours to days." It was a phreatic eruption and phreatomagmatic eruption from the main crater that spewed ashes to Calabarzon, Metro Manila, some parts of Central Luzon, and Pangasinan in Ilocos Region, resulting in the suspension of classes, work schedules, and flights. By January 26, 2020, PHIVOLCS observed inconsistent, but decreasing volcanic activity in Taal, prompting the agency to downgrade its warning to Alert Level 3. After February 14, Alert status was set to Level 2 because of overall decreasing trend of volcanic activities, but it does not mean that the threat of an eruption has disappeared. In addition, the Alert Level can be raised to Alert Level 3 if there is a symptom of increasing unrest at any time.

• Economic and Environmental Geology
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• v.31 no.6
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• pp.473-483
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• 1998

The igneous rocks in the Goseong area are composed of the volcanic rocks (andesitic lapilli tuff and rhyodacite), Bulgugsa granites (Hornblende-biotite granite and two pyroxene granite) and intrusive andesites. In the variation diagrams of the trace and rare earth element contents and elemental ratios as well as the REE patterns, the three igneous rock types show different variational trends and patterns. The geochemical features represent that the igneous rocks in the area were formed from three different magmatic pulses. Two independently carried out Rb-Sr isotope experiments for the Goseong granites show that the whole rock ages and Sr initial ratios of the granites are $66.4{\pm}6.2Ma$, $0.70517{\pm}22(2{\sigma})$ and $71.3{\pm}6.8Ma$, $0.70506{\pm}18(2{\sigma})$, respectively. These results suggest that the granites magma originated from the lower crustal materials of igneous origin intruded into the area during the late Cretaceous period. Masan hornblende-biotite granite emplaced at the vicinity of the Goseong area is very similar to the Goseong granite in its mineral compositions, major, trace and rare earth element contents and patterns. The intruding age (100 Ma) of the Masan granite is order than that of the Geseong granite, however. The similarity of the geochemical natures but the contrast of the intruding ages between the Masan and Goseong granites possibly indicate that the magma generation from the same source materials occurred at a temporal interval of ca. 30 Ma.

• The Journal of the Petrological Society of Korea
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• v.8 no.2
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• pp.81-91
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• 1999

The area of the study is located in Ogcheon district, middle part of Ogcheon Fold Belt. The area is covered by metasedimentary rocks of Ogcheon Supergroup at northern, eastern and southern part. Jurassic Ogcheon granite which intruded into Ogcheon Supergroup at central part, was intruded by Cretaceous quartz porphyry at western part. The granite consists of quartz, plagioclase, alkali feldspar, biotite, sphene, apatite, epidote, opaque and so on. It is generally characterized by grey to light grey, medium-grained, mafic enclave and partly weak foliation. In terms of geochmical compositions, the granite is felsic, peraluminous, subalkaline and calc-alkaline, and it was differentiated from single granitic magma. It shows parallel LREE enrichment and HREE depletion patterns with 0.84 Eu negative anomaly, which has REE variation trend and anomaly value similar to Jurassic granites in Korea. From charactristics of petrology, mineralogy and geochmistry, it may be interpreted that the Ogcheon granite body was derived from melting of I-type crustal material related to syn-collisional tectonic setting and emplaced more or less rapidly into the Ogcheon Supergroup.

• Economic and Environmental Geology
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• v.10 no.1
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• pp.19-35
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• 1977

The study area is located in between Hacheonri and Weolgulri, Jecheon-gun where the formations of Okcheon group and Chosun group come in contact and the stratigraphy and geological age of the Okcheon group have been debated among previous workers. The dolomitic limestone which distributed at Cheongam and Dumusil is clarified as the Hyangsanri dolomite formation and the quartzite distributed at Cheongam and Howeunri as Taehyangsan quartzite formation. The newly named Soorumsan schist interbedded in the Great Limestone Series was previously classified Seochangri formation. It is also classified that the formation formerly named as Seochangri was divided into newly named Manji schist which seems to be correlated to Kemyeongsan and Munjuri formation. The formation formerly named as Buknori is clarified as Hwanggangri formation. The Samtaesan formation has been clarified as the lower and upper limestone beds which belong to the Great Limestone Series. The area divided into two groups, that is, Okcheon system of Pre-cambrian age occupies western part and the Great Limestone Series of Chosun system of Cambro-Ordovician age eastern part of this area. Okcheon system consists in ascending order of Manji schist, Hyangsanri dolomite, Taehyangsan quartzite, Munjuri schist, and Hwanggangri formation of meta-tillite. The Great Limestone Series of Chosun group consists in ascending order of lower limestone, Soorumsan schist, Hoosanri quartzite and upper limestone formations. Busan augen gneiss seems to be igneous origin. Unmetamorphosed shale interbed can be traced in the Soorumsan schist. Previous study (Kims, 1974) reveals that meta-volcanic rocks are distributed from south to north along contact zone of the Okcheon and Chosun groups, and it has been confirmed that the meta-volcanics crop out continuously from the adjacent southern quardrangle into the southern part of the area studied, intruding along the fault zone between the Okcheon and Chosun groups which seems to be upthrust as in the area south. This evidence coincides with Kims' work (1974) which states that the Precambrian Okcheon group is largely overturned and thrusted over the Chosun group.

• Ocean and Polar Research
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• v.24 no.4
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• pp.465-482
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• 2002

Petrological, geochemical, and geochronological studies of Dokdo volcanic rocks, East Sea, have been carried out to understand their petrogenesis. Dokdo volcanic activity is divided into three stages according to occurrences and eruption ages of rocks. The second-stage activity is accompanied by large volume of pyroclastics and lavas of intermediate composition, and occupies most of the East and West islets. K-Ar biotite and whole-rock ages indicate that Dokdo volcanic activity occurred during late Pliocene and became systematically younger toward later stages: namely, 2.7-2.4 Ma for the first-stage trachyte, 2.4-2.3Ma for the second-stage trachyandesite and 2.2-2.1 Ma for the last-stage trachyte and dikes. Dokdo volcanic rocks are of intermediate to felsic compostions, and have OIB-like alkaline nature. The geochemical similarities between Dokdo and Ulleungdo volcanic rocks suggest that they were formed from the same mantle plume. However, considering the difference of eruption ages between Dokdo (2.7-2.1 Ma) and Ulleungdo (1.4-0.01 Ma) volcanic rocks, the former seems to have been formed by earlier hot spot activity.

• The Journal of the Petrological Society of Korea
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• v.18 no.4
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• pp.349-370
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• 2009

The Mt. Dungjuribong Volcanic Complex located in Gurye-gun, southwest of Ryeongnam massif, composed of Cretaceous andesitic rocks and rhyolite. $SiO_2$ contents of the volcanic rocks range from 52.0 to 78.5 wt.%. The major and trace elements composition, REE patterns and tectonomagmatic discrimination diagrams of volcanic rocks suggest that they are typical of continental margin arc calc-alkaline rocks produced in the subduction environment. The phenocrysts of the volcanic rocks show that they had gone in disequilibrium state, such as reversal zoning and resorbed core of plagioclase, reaction rim around pyroxene and resorbed margins of quartz, which showing the evidence of magma mixing during the evolution of magma.

• The Journal of the Petrological Society of Korea
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• v.28 no.4
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• pp.307-317
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• 2019

Petrological studies were performed on the Sanbangsan lava dome, located in the southwest of Jeju Island Volcanic Field. According to the lava ejection method, it is 'an internal primitive form' that is gradually pushed up and expanded by continuous magma injection from the bottom to the top of the vent and it corresponds to the 'low lava dome'. The rocks are partly plotted in the field of benmoreite, but mostly plotted in the field of trachyte of the Cox et al.(1979) classification diagram, and also mainly plotted in the field of trachyte of Le Maitre et al.(2002) and Zr/TiO₂-Nb/Y classification diagram. Therefore, the expression that described the rock of Sanbangsan lava dome as 'trachy-andesite' should be corrected to 'trachyte'. The volcanic rocks that consists in the Sanbangsan lava dome are trachyte containing normative quartz and shows differentiation trend in the range of 59.75-63.46 wt.% SiO₂.