• The Journal of the Petrological Society of Korea
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• v.5 no.1
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• pp.108-120
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• 1996

This study reports petrography and geochemical characteristics of the Cretaceous volcanic rocks that are distributed in the vicinity of the Cheonsungsan area, Yangsan-Gun, Gyeongsangnam-Do. The Cretaceous volcanic rocks composed of andesitic rocks, Wonhyosan tuff, Cheonsungsan tuff in ascending order. Sedimentary rock is the basement in the study area cofered with volcanic rocks. These volcanic rocks are Wonhyosan tuff and Cheonsungsan tuff that represented the early phase of the Bulgugsa igneous activity. Wonhyosan tuff are classified into dacite tuff and dacite welded tuff based on the rock texture and their mineral composition. They are covered with Cheonsungsan tuff. Dacite tuff composed of lithic lapilli ash-flow tuff and vitric ash-flow tuff. Most dacite welded tuff are lapilli ash-flow tuff. Cheonsungsan tuff overlying the Wonhyosan tuff consists of rhyolite tuff and rhyolite welded tuff. Rhyolite tuff are lithic crystal ash-flow tuff and crystal vitric ash-flow tuff with somewhat accidental fragments of andesitic and sedimentary rocks. Rhyolite welded tuff is distinguishe from rhyolite tuff by is typical eelded fabrics and its rock color. According to petrochemical data, the volcanic rocks in study area belong to high-K orogenic suties. On the discriminant diagrams such as La/Yb versus Th/Yb, these rocks falls into the discriminant fields for the normal continental margin arc.

• Economic and Environmental Geology
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• v.24 no.3
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• pp.261-276
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• 1991

The main aspect of this study are to clarify igneous activity of igneous rocks, which is a member of various intrusives and volcanics exposed in Naju-Namchang area of southern central zone of Ogcheon Geosynclinal Belt, southern part of Youngdong-Kwangju depression zone of tectonic provinces in Korea. Naju-Namchang area are subdivided into three rock belts based on occuring of Cretaceous granites. Three rock belts consist of foliated granites, Jurassic granites and Cretaceous granites in central granitic rock belt (C-C), and acidic tuff and lavas in northwest volcanic rock belt(C-NW) and southeast volcanic rock belt(C-SE). Chemical composition of these igneous rocks show mostly similar trend to the Daly's values on Harker diagram and correspond to VAG + Syn-COLG region on Pearce's discrimination diagram. These igneous rocks vary wide range in total REE amount(37.4-221.3ppm) characterized by enriched LREE content and steep negative slope in Eu(-) anomaly. It is concluded each synchronous granites which composed of serveral rock facies is considered to formed by differentiation of co-magma at continental margin, and igneous activity of study area are two more Pre-Cambrian Orogenies, Songrim Disturbance, Daebo Orogeny and Bulkuksa Disturbance.

• The Journal of the Petrological Society of Korea
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• v.21 no.1
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• pp.1-12
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• 2012

The Baegdusan volcano is one of the most active volcanoes in northeastern Asia, and the 10th century eruption was the most voluminous eruption in the world in recent 2,000 years. During the period from 2002 to 2005, volcanic earthquakes and abnormal surface distortions by suspected subsurface magma intrusion beneath the volcano were observed in the Baegdusan area. Seismic activity has gradually increased with earthquake swarms during 2002-2003 and hundreds of seismic event in a day, especially annual peak of 2,100 in 2003. Then the number of seismic activity has declined since 2006 to the background level in 1999-2001. According to the typical frequency of volcanic earthquakes in the Baegdusan volcano, the frequency distribution of typical volcanic earthquakes between 2002 and 2005 indicates that all the main frequency of the earthquakes basically falls down less than 5 Hz and 5-10 Hz. These events are all the VT-B and LP events caused by the shallow localized fracture and intrusion of magma. The horizontal displacement measurement by GPS during the period from 2000 to 2007 of the Baegdusan stratovolcano area indicates that an inflated process has been centered at the summit caldera since 2002. The displacement between 2002 and 2003 reached at a maximum value of 4 cm. After 2003, the deformation rate of the volcano continued to decrease with unusual variation during the period from 2006 to 2007. After 2003 the vertical displacement uplift rate falls down gradually but still keeps in an uplift trend in northern slope. It is generally believed that when $^3He/^4He(R)$ in a gas sample from a hot spring exceeds $^3He/^4He(R)$ in the atmosphere, it can be concluded that mantle-source. And temperatures of hot springs are rising steadily to $83^{\circ}C$. It is unrest signals at the Baegdusan, which is potentially active. The Baegdusan volcano is now in unrest status, there is eruption threat in the near future. Intensified monitoring and emergency response plan for volcanic risk mitigation are urgent for the volcano.

• Journal of the Korean earth science society
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• v.34 no.6
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• pp.470-478
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• 2013

There have been a number of observed precursors of volcanic activities- such as volcanic earthquake, surface inflation, specific volcanic gas emission, temperature of hot spring- at Mt. Baekdusan since 2002. We identified the increase of the volume of magma chamber beneath Mt. Baekdusan as we observed an inflation trend of vertical and horizontal surface displacement around Cheonji caldera lake by using precise leveling data from 2002 to 2009. The surface displacement trend changed to deflation in 2010, and the trend changed to inflation again after a while. Utilizing the data of inflated surface (46.33 mm) on the northern slope of Mt. Baekdusan from 2002 to 2003, we calculated the volume change of magma chamber beneath the Mt. Baekdusan. The volume change was about 0.008 $km^3$ ($7.7-8.0{\times}10^6m^3$) from 2002 to 2003. It indicated that a new magma (0.008 $km^3$) injected to the magma chamber 5 km below Mt. Baekdusan.

• 한국지구물리탐사학회:학술대회논문집
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• 2009.05a
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• pp.57-65
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• 2009

Selection of good mineralized area is a combination of the integration of all the available geo-scientific (i.e., geological, geochemical, and geophysical) information, extrapolation of likely features from known mineralized terrenes and the ability to be predictive. The time-space relationships of the hydrothermal deposits in the East Asia are closely related to the changing plate motions. Also, two distinctive hydrothermal systems during Mesozoic occurred in Korea: the Jurassic/Early Cretaceous deep-level ones during the Daebo orogeny and the Late Cretaceous/Tertiary shallow geothermal ones during the Bulguksa event. Both the Mesozoic geothermal system and the mineralization document a close spatial and temporal relationship with syn- to post-tectonic magmatism. The Jurassic mineral deposits were formed at the relatively high temperature and deep-crustal level from the mineralizing fluids characterized by the relatively homogeneous and similar ranges of ${\delta}^{18}O$ values, suggesting that ore-forming fluids were principally derived from spatially associated Jurassic granitoid and related pegmatite. Most of the Jurassic auriferous deposits (ca. 165-145 Ma) show fluid characteristics typical of an orogenic-type gold deposits, and were probably generated in a compressional to transpressional regime caused by an orthogonal to oblique convergence of the Izanagi Plate into the East Asian continental margin. On the other hand, Late Cretaceous ferroalloy, base-metal and precious-metal deposits in the Taebaeksan, Okcheon and Gyeongsang basins occurred as vein, replacement, breccia-pipe, porphyry-style and skarn deposits. Diverse mineralization styles represent a spatial and temporal distinction between the proximal environment of sub-volcanic activity and the distal to transitional condition derived from volcanic environments. However, Cu (-Au) or Fe-Mo-W deposits are proximal to a magmatic source, whereas polymetallic or precious-metal deposits are more distal to transitional. Strike-slip faults and caldera-related fractures together with sub-volcanic activity are associated with major faults reactivated by a northward (oblique) to northwestward (orthogonal) convergence, and have played an important role in the formation of the Cretaceous Au-Ag lode deposits (ca. 110-45 Ma) under a continental arc setting. The temporal and spatial distinctions between the two typical Mesozoic deposit styles in Korea reflect a different thermal episodes (i.e., late orogenic and post-orogenic) and ore-forming fluids related to different depths of emplacement of magma (i.e., plutonic and sub-volcanic) due to regional changes in tectonic settings.

• Geophysics and Geophysical Exploration
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• v.9 no.1
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• pp.129-138
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• 2006

Helicopter-borne aeromagnetic surveys at two different times separated by three years were conducted to better understand the shallow subsurface structure of the Vulcano and Lipari volcanic complex, Aeolian Islands, southern Italy, and also to monitor the volcanic activity of the area. As there was no meaningful difference between the two magnetic datasets to imply an apparent change of the volcanic activity, the datasets were merged to produce an aeromagnetic map with wider coverage than was given by a single dataset. Apparent magnetisation intensity mapping was applied to terrain-corrected magnetic anomalies, and showed local magnetisation highs in and around Fossa Cone, suggesting heterogeneity of the cone. Magnetic modelling was conducted for three of those magnetisation highs. Each model implied the presence of concealed volcanic products overlain by pyroclastic rocks from the Fossa crater. The model for the Fossa crater area suggests a buried trachytic lava flow on the southern edge of the present crater. The magnetic model at Forgia Vecchia suggests that phreatic cones can be interpreted as resulting from a concealed eruptive centre, with thick latitic lavas that fill up Fossa Caldera. However, the distribution of lavas seems to be limited to a smaller area than was expected from drilling results. This can be explained partly by alteration of the lavas by intense hydrothermal activity, as seen at geothermal areas close to Porto Levante. The magnetic model at the north-eastern Fossa Cone implies that thick lavas accumulated as another eruption centre in the early stage of the activity of Fossa. Recent geoelectric surveys showed high-resistivity zones in the areas of the last two magnetic models.

• The Journal of the Petrological Society of Korea
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• v.15 no.2 s.44
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• pp.90-105
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• 2006

The Cretaceous volcanic rocks in the study area represented by andesitic rocks occupy eastern part of the Kyeongsan Caldera. The volcanic rocks comprise andesite I, andesitic tuff, andesite II, and andesitic tuff breccia in their stratigraphic succession, and andesitic porphyry. Andesite I is distinguished from andesite II in their color, texture, phenocryst mineralogy and petrochemisty. In outcrops, andesite I is compact and dark-green, and andesite II is brick red in color and porphyritic in texture. In their phenocryst mineralogy, andesite I contains olivine phenocryst in addition to plagioclase and pyroxene which occur in both of andesites. Compared to andesite II, andesite I is higher in $SiO_2$ and $K_2O$ contents and lower in CaO, MgO, MnO, $TiO_2,\;Fe_2O_3$, and $P_2O_5$. Major elements petrochemistry shows that magma series of the volcanic rocks spread widely from calc-alkaline to alkaline series. On the other hand, immobile trace elements petrochemistry shows that the magma series is calc-alkaline without exception, suggesting that the volcanics has experienced more or less alkali enrichment after their eruption. Trace element diagrams for discrimination of tectonic setting show that the volcanics of the study area might be originated from calc-alkaline continental volcanic arc.

• The Journal of the Petrological Society of Korea
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• v.25 no.4
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• pp.409-419
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• 2016

The number of volcanoes erupted during the past ten thousand years(Holocene period) on this planet is known to stand around 1,520. Of those volcanoes, the number of active volcanoes during the six-years and seven-month period(January 2010 through the end of July 2016) is totals 209. These findings show that an average of approximate 90 volcanoes erupted every year since 2010. It is also found that over 90 percent of those active volcanoes took place in the circum-Pacific volcanic belt, which is commonly called 'Ring of Fire'. This status coincides with the distribution maps of active volcanoes on the earth: about 80 percent on subduction zone of the convergence of lithospheric plate; 15 percent on spreading zone; 5 percent on intra-plate zone. The period given in this research during 350 weeks, the following three volcanoes showed a frequency of more than 300 times eruption: Kilauea(Hawaii, USA, 338 times), Sheveluch(Kamchatka, Russia, 337 times), and Aira(Kyushu, Japan, 301 times). According to the survey conducted during the given period, there is no conspicuous increase in the frequency of volcano activities. It rather shows that volcanic eruptions took place almost evenly every year.

• Journal of the Korean earth science society
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• v.22 no.1
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• pp.10-19
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• 2001

There are three scoria cones and their eruptive materials in Sarabong-Byeoldobong-Hwabukbong area Cheju Island. And they made complicated volcanic stratigraphy. In Byeoldobong tuff, basalt and granite xenoliths are present. It is presumed that the granite is a kind of basement of Cheju island. And Biseokgeori hawaiite has many kaersutite phenocrysts. Therefore, this area is very important for the study about history of volcanic activity of Cheju island. The lowest beds are Shinheung basalt and Byeoldobong tuff. Byeoldobong tuff has xenoliths of granite and phenocrystalline basalt. After the formation of these rocks, the Hwabukbong volcanism commenced. First of all this volcanism formed Biseokgeori hawaiite that has lots of kaersutite, a member of amphibole group, characteristically. Over this rock, Hwabukbong scoria cone was formed. The next Sarabong volcanism effused Keonipdong hawaiite that has lots of plagioclase and olivine phenocrysts and then Sarabong scoria cone was made up. Basalt xenolith in Byeoldobong tuff is different from Shinheungri basalt with regard to petrography, therefore this offers suggestion about existence of another basalt between basement and Shinheungri basalt. Granite xenolith derived from the basement of this area has features of the Jurassic granite in the Korea Peninsula, for example a lot of myrmekitic texture, microcline, and absolute age (172.4 Ma) by K-Ar method.

• The Journal of the Petrological Society of Korea
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• v.7 no.1
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• pp.27-36
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• 1998

The volcanic piles in the northern Yucheon Minor Basin area are the Hagbong basaltic rocks, the Chaeyaksan basaltic rocks, the Jusasan andesitic rocks, the Unmunsa rhyolitic rocks, and the Tertiary voicanics. Stratigraphically, from the lowermost, (1) the Hagbong basaltic rocks are composed mainly of basaltic tuff with two olivine basalt flows intercalated, (2) the Chaeyagsan basaltic rocks are predominantly in tuffs and agglomerate with 3 basaltic flow interlayers, (3) the Jusasan andesitic rocks consist of thick piles of alternated sequences of 4 andesite flows and 5 andesitic tuffs and tuffaceous sediments and (4) the Unmunsa rhyolitic rocks which embed some rhyolite and obsidian are dominant in tuffs such as ash flow and crystal welded tuff. These volcanics reveal distinguishable characteristics in petrochemistry. In discriminating by major elements, the Hagbong and the Chaeyagsan basaltic rocks are alkaline, whereas the latter is also spilitic. In comparison, the volcanic rocks of the Jusasan andesitic rocks and the Tertiary sequences are characteristically calc-alkaline although their distribution is spatially separated. On the other hand, the variations in immobile trace elements indicate that the Hagbong basaltic rocks range from alkaline to calc-alkaline and from WPB/VAB transition to VAB, whereas the Chaeyagsan basaltic rocks are calc-alkaline WPB/VAB transition type and the two others calc-alkaline VAB. In order to show such a variety in their rock series of the volcanic rocks, the environment during their magma generation, magma rising, and post-eruption alteration could be positively considered.