• Journal of Korean Society of societal Security
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• v.2 no.2
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• pp.23-30
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• 2009

• The Journal of the Petrological Society of Korea
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• v.26 no.1
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• pp.1-11
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• 2017

We have dated the K-Ar, Ar-Ar and U-Pb ages of the Masan hornblende-biotite granite in the southern Cretaceous Gyeongsang basin to constrain its emplacement age. The ~108 Ma hornblende K-Ar age obtained in the study is similar to the previously reported Rb-Sr age. However, the single grain total fusion $^{40}Ar/^{39}Ar$ dating on hornblende failed to yield statistically meaningful ages because the isotopic system was open during its alteration. Thus the hornblende K-Ar age in the study is also unlikely to be reliable. The single grain total fusion $^{40}Ar/^{39}Ar$ dating on biotite yielded an average age of $75.8{\pm}3.0Ma$. Apart from scattered data in the range of ~45-75 Ma, the average age increased to ~80 Ma. The SHRIMP and LA-MC-ICPMS U-Pb isotopic compositions of zircon from the Masan hornblende-biotite granite yielded its emplacement age as $87.6{\pm}2.7Ma$ and $86.8{\pm}0.4Ma$, respectively. It is thus likely that the ~80 Ma $^{40}Ar/^{39}Ar$ age of biotite might reflect the cooling age of Masan hornblende-biotite granite or the thermal influences from later intense igneous activities in the Gyeongsang basin.

• Proceedings of the Petrological Society of Korea Conference
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• 2009.05a
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• pp.153-153
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• 2009

• Economic and Environmental Geology
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• v.14 no.4
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• pp.183-191
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• 1981

Major and trace elements analyses are presented for 13 amphibolites by wet chemical and emission spectroscopic methods. These chemical data were compared with limestone and quartzite closely associated with the amphibolites. The chemical similarity of the amphibolites studied to the basic igneous rock and low oxidation ratios (<30) are indicative of the igneous intrusive, especially middle stage differentiates. Petrographic and stratigraphic study of the rocks suggest the more igneous features rather than those of sedimentary progenitors.

• Journal of the Mineralogical Society of Korea
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• v.17 no.4
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• pp.357-364
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• 2004

Mineral chemistry of talc from the Dongyang talc deposits was studied to characterize the differences between dolomite-origin talc (talc I) and tremolite-origin talc (talc II). Average iron and aluminum contents are higher in talc II, 2.18 wt% FeO and 0.31 wt% $Al_2$O$_3$), than in talc I, 1.48 wt% FeO and 0.08 wt% $Al_2$O$_3$). Consistently lower Mg/(Mg+Fe+Mn) ratios and higher AI concentrations with uniform values of talc II compared to talc I seem to reflect the compositional differences of the original materials, tremolite and dolomite, respectively. Relative enrichment of Al as well as Fe in talc II compared to tremolite can be attributed to their immobile behaviors during alteration process and the rapid diffusion of hydrothermal fluids, which can accelerate instantaneous nucleation with immaturity growth of talc II. Increase in the concentrations of talc II can lower the ore grade by increasing concentrations of impure components such as AI and Fe, and by abundant presence of tremolite as well.

• The Journal of the Petrological Society of Korea
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• v.10 no.2
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• pp.57-81
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• 2001

In the amphibolites of the Hwanggangri area, three metamorphic zones are established like hornblende-actinolite zone (H-AZ), hornblende zone (HZ) and diopside zone (DZ) by the main mineral assemblages. Hornblende zone and hornblende-actinolite zone develope away from the diopside zone that experienced the highest thermal effect. Thus, this pattern identifies the decreasing metamorphic grade of the contact metamorphism with increasing distance from the granitic pluton. The mineral assemblages of this rock are classified into six representative groups such as $\circled1$ actinolite+plagioclase+chlorite, $\circled2$ actinolite+hornblende+plagioclase+chlorite$\pm$epidote$\pm$biotite, $\circled3$ actinolite+hornblende+plagioclass$\pm$biotite$\pm$epidote, $\circled4$ hornblende+plagioclase$\pm$biotite$\pm$chlorite, $\circled5$ hornblende+plagioclase+diopside+actinolite$\pm$epidote$\pm$chlorite, $\circled6$hornblende+plagioclase+diopside$\pm$biotite$\pm$epidote. Two metamorphic events m recognized in the amphibolites of the study area that the first metamorphism is the regional metamorphism dominantly occurred in the whole Ogcheon metamorphic belt and it gave rise to the growth of actinolite at the core or center of the amphibole grains of coarse and medium size. Its metamorphic grade ranges from the greenschist facies to epidote-amphibolite facies. The second metamorphism overlapped is the contact metamorphism caused by the adjacent granitic pluton, and its metamorphic grade is thought to reach to the low pressure part of upper amphibolite facies. According to the calculation by TWEEQU thermobarometry and amphibole-plagioclase thermometry, the metamorphic temperature of initial regional metamorphism is $439-537^{\circ}C$ under pressure of 4.6-7.3 kb and its peak temperature and pressure are considered to reach to the range of 492-537 and 5.2-7.3 kb. And the temperature range of contact metamorphism occurred by intrusion of cretaceous granitic body, is $588-739^{\circ}C$ under pressure of 2.6-5.2 kb and its peak temperature and pressure are estimated as having the range of $697-739^{\circ}C$ and 3.8-5.2 kb that this amphibolites are estimated to pass through the metamorphic evolution of both the rise of temperature and the drop of pressure.

• Korean Journal of Mineralogy and Petrology
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• v.33 no.3
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• pp.259-272
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• 2020

The seismic properties in the crust are affected by the lattice preferred orientation(LPO) of major minerals in the crust. Therefore, in order to understand the internal structure of the crust using seismic data, information on the LPO of the major constituent minerals and the seismic properties of major rocks in a specific region are needed. However, there is little research on the LPOs of minerals in the crust in Korea. In this study, we collected amphibolites from two outcrops in Wigokri, Gapyeong, located in the nothern portion of Gyeonggi Massif, and we measured the LPOs of major minerals of amphibolite, especially amphibole and plagioclase through EBSD analysis, and calculated seismic properties of amphibolite. Two types of LPOs of amphibole, which are defined as type I and type IV, were observed in the two outcrops of Gapyeong amphibolites, respectively. In the case of amphibolites with the type I LPO of amphibole, large seismic anisotropy of both P- and S-wave was observed, while in the amphibolites with the type IV LPO of amphibole, small seismic anisotropy was observed. This is consistent with previous experimental results. The polarization direction of the fast S-wave was aligned subparallel to the lineation regardless of the LPO types of amphibole. The seismic anisotropy observed in Gapyeong is expected to be helpful to interpret the structure and seismic data within the crust in Gyeonggi Massif.

• The Journal of the Petrological Society of Korea
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• v.8 no.2
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• pp.92-105
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• 1999

The Cretaceous Chaeyaksan basaltic rocks consist mainly of basaltic tuffs intercalating three layers of basalt. Stratigraphically, the rocks are located between the upper Songnaedong Formation and the lower Geoncheonri Formation and contain plagioclase, augite, hornblende, and a few olivine phenocrysts. Geochemically, they show calc-alkaline characteristics in some immobile element content, but show the alkaline suite feature in the mobile major element composition. The basalts are widely spilitized but some of them is altered to shoshonitic rocks with more calcic plagioclase, calcite, and chlorite, and adularia veinlets are common in the rocks. It is supposed that the post-eruption alteration of the rocks is done through alkali-replacement by hydrothermal solution or vapor rather than by low grade regional metamorphism. It is considered that A1 in hornblende will be available for estimating the pressure of the pre-eruption magma in the reservoir although the plagioclase of the rocks are highly albitized. The crystallization pressure was calculated as 5.7Kb by the equation of Johnson and Rutherford(l989) incorporating of the effect of overestimate of .41T in hornblende in the case of quartz-free rocks. Application of the estimated temperature, pressure and the constituent of phenocrysts of the rocks to the experimental P-T phase diagram for basalts established by Green(1982) indicates the crystallization course and succession of growth of the phenocrysts during of rising and cooling of the magma reservoir; augite + augite and olivine + augite, olivine, and hornblende -+ augite and hornblende+ augite, hornblende, and plagioclase. Such evolution course of the magma may include crystal fractionation by the phenocrysts crystallization and contamination by country rock in lower crust.

• The Journal of the Petrological Society of Korea
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• v.28 no.4
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• pp.279-298
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• 2019

Mupung granite, which is located adjacent to Gimcheon granites to the north and Geochang granites to the south, has been known to consist of biotite-hornblende granite (Gbh), porphyritic granite (Gp), and hornblende-biotite granite (Ghb). In this study, we subdivided the Gbh of Mupung granite into biotite granite (Gb) and biotite hornblende granite (Gbh), based on petrological observations. The grayish Gb with medium to coarse grain and porphyritic texture contains a small amount of muscovite, but the hornblende and mafic microgranular enclave (MME) is not observed in Gb. On the other hand, MME can be commonly found in pinkish Gbh. The mafic minerals in Gbh are mostly hornblende and biotite. In the Gb in Mupung granites, the hornblende and sphene (which is the characteristic minerals in Gimcheon granite) are not observed. In addition, the trend of the changes in major elements of Gb in Mupung granites is similar to that of Geochang granites. These petrological characteristics suggest that the Gb in Mupung granite has a similarity with Geochang granite (than Gimchen granite). We also observed that the texture and composition of minerals of Gbh, as well as those of surrounding Gp and Ghb, are consistent with the characteristics of Cretaceous granites in Gyeongsang basin, rather than those of Jurassic granites in Yeongnam massif.

• The Journal of the Petrological Society of Korea
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• v.17 no.3
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• pp.154-165
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• 2008

Rock bowls and pots used in restaurants are one of the popular usages of natural rocks in Korea. Most rock bowls and pots are made of Mg- and Ca-rich amphibolite composed of hornblende, actinolite, tremolite, diopside, plagioclase. Hornblende occurs as prismatic crystal habit, and belongs to Mg-hornblende to tschermakite. Actinolite and tremolite occur as acicular form (aspect ratio $0.10{\sim}0.13$), and ranges 0.65 to 0.90 in Mg/(Mg+Fe) ratio. These acicular actinolite and tremolite are non-asbestos minerals. However to use of rocks containing these minerals as tableware it is needed to regulatory guidelines for stability and utility based on petrological and mineralogical characteristics. Discrepancy of rock occurrence and mineral chemistry between commercial rock bowls and original rocks indicate that most rock bowls are made of uncertain amphibolite in original location. Consequently, there is a potential risk to use inappropriate amphibolites as tableware. Therefore, it is needed to systematically research on geology and biology, and manage commercial rock bowls and pots used in Korean restaurants.