• The Journal of the Petrological Society of Korea
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• v.17 no.3
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• pp.166-178
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• 2008

The modal analyses on the phenocryst phases and the normative mineralogies from the bulk chemical analyses record that the volcanic rocks related to the Yangsan caldera might been derived from compositionally zoned magma. The volcanic rocks show linearly continuous mineralogical gradients, not only totally in the relations between $SiO_2$ and proportion of phenocryst content, but also within each rock unit in the relations between total phenocryst content and the proportion, Q-Ab-Or and Q-An(Ab-Or) diagrams. The roughly gradational modal variations of the phenocryst phases are shown upward within each rock unit. However, the contents and proportion of the phenocrysts in the Yangsan Tuff and the Hwajeri Formation represent the zigzaggedly undulatory variations. The continuous mineralogical gradients without large gaps define a large zoned magma system in the pre-eruptive, later precollapse and postcollapse magma chambers respectively. The zigzagged variations reflect the intermittent eruptive pulses representing any time gaps.

• The Journal of the Petrological Society of Korea
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• v.26 no.4
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• pp.311-325
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• 2017

Peridotite xenoliths in middle Miocene alkaline basalt from the Mt. Baekdu area are mainly anhydrous spinel lherzolites, displaying coarse-grained protogranular texture. These xenoliths have late-stage secondary orthopyroxene replacing olivine as the metasomatic mineral and glass formed along the grain boundaries. The studied xenoliths are characterized by the high $Mg{\sharp}[=100{\times}Mg/(Mg+Fe_{total})$ atomic ratio] of olivine, orthopyroxene and clinopyroxene (89~92) and the $Cr{\sharp}[=100{\times}Cr/(Cr+Al)$ atomic ratio] of spinel (10~29). Based on major-element data, the studied xenoliths are similar to those from the abyssal peridotites. Clinopyroxenes of the xenoliths are mostly enriched in incompatible trace elements, exhibiting two types of REE patterns: (1) LREE-depleted with $(La/Yb)_N$ of 0.1~0.2 and $(La/Ce)_N$ of 0.4~0.8. (2) LREE enriched with $(La/Yb)_N$ of 2.2~3.8 and $(La/Ce)_N$ of 1.2~1.6. The calculated equilibrium temperatures and oxygen fugacities resulted in $920{\sim}1050^{\circ}C$ and ${\Delta}fO_2(QFM)=-0.8{\sim}0.2$, respectively. It is suggested that the Mt. Baekdu peridotite xenoliths represent residues left after variable degrees of melt extraction(less than 15 vol%), which was subsequently subjected to different degrees of modal/cryptic metasomatism by silica- and LREE-enriched fluids (or melts).

• The Journal of the Petrological Society of Korea
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• v.7 no.1
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• pp.53-68
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• 1998

Microstructural and rock structural analyses on the deformed Cheongsan granite characterized by abundant K-feldspar megacrysts have been carried out to understand the temperature condition for the ductile shear deformation. In K-feldspar, microkinks, microfractures and core-and-mantle structures without the development of subgrains in outer core-zone are the most common microstructures observed. Myrmekites and flame perthites are developed at the strain-localized areas along the microfractured K-feldspar. In plagioclase, microfractures, deformation twins and kink bands are predominant. The deformation twins cut across the igneous zonation of the plagioclase. Patterns of c-axis fabrics of dynamically recrystallized new quartz grains display single girdle and type II crossed girdle where prism slip system is predominant. These characteristic microstructures produced during the ductile shearing suggest that the ductile shear deformation in the Cheongsan granite occurred under epidote-amphibolite conditions($400-500^{\circ}C$). Three main shear zones are recognized at outcrop scale: discrete shear zone with anastomosing high-strain domain, shear zone with pervasive S-C structure and shear zone with homogeneously foliated domain. Geometric features of these shear zones produced during the ductile shear deformation are controlled by amount of strain under the $400-500^{\circ}C$ deformation temperature.

• The Journal of the Petrological Society of Korea
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• v.5 no.2
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• pp.188-199
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• 1996

Boeun granodiorite, which intruded into the metasedimentary rocks of the Ogcheon Group, show chemical natures of metaluminous and calc-alkaline. Generating and emplacing environment of the Boeun granodiorite would have been a active continental margin. Comparing to the contemporaneous Inje-Hongcheon granodiorite in the Gyeonggi massif, the Boeun granodiorite seems likely to have formed under more immature continental arc environment. Compositional changes of major, trace and rare earth elements in granodiorite and felsic dyke are not certain to indicate crystallization differentiation. From this fact, the simple fractional crystallization model would be in question to explain the magma process which controlled the formation of the Boeun granitic mass. The model calculations for Rayleigh fractionation, fractionation with variable major-component composition, assimilation-fractional crystallization (AFC) were carried out to examine the magma process of the mass. The results of former two models do not agree with the compositional variations in the mass. The AFC model can be, however, applied to the magma process. The conditions for AFC process are (1) composition of assimilated wallrock is similar to that of primary magma. (2) assimilating rate is similar to crystallizing rate, and (3) mass of assimilated wallrock is about 10% of that of the magma. These conditions deny a possibility that the assimilated wallrock was the metasedimentary rocks of the Ogcheon Group. This indicates that after having experienced the assimilation process in deeper crust, the granodiorite magma intruded into the Ogcheon group. Every model calculating suggests that the felsic dyke was differentiated not from the granodiorite magma, but from a different source magma.

• 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.

• Journal of the Mineralogical Society of Korea
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• v.23 no.1
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• pp.63-71
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• 2010

The artificial rains having different pH and weathering simulation test were performed for Gyeongju Namsan granite and dacitic tuff to predict the role of acid rain in the deterioration of stone monuments located in Gyeongju area. The pH 4.0 rain reacted with the fresh granite showed near neutral pH at the early stage due to the hydrolysis of minerals in the rock surface. But the pH changed back to the initial pH in the later stage. On the other hand, the pH 5.6 rain showed the neutral pH for a longer time than the experiment with pH 4.0 rain, reflecting slower reaction of minerals due to the weaker acidity. When the pH 5.6 rain reacted with the weathered granite, the water showed neutral pH longer than the case of the fresh granite. The similar tendencies were observed in the experiment of dacitic tuff, except that the pH 4.0 rain reacted with dacitic tuff took a longer time to go back to the initial pH as compared with the case of granite. These results may due to the differences in mineral composition and texture of two rocks. Dacitic tuff contains more fine-grained or glassy groundmass than granite and is more reactive with weaker acid rain. It was predicted that the weight loss and strength decrease rate of dacitic tuff would be approximatetly twice relative to those of granite in the same experimental environment.

• Korean Journal of Remote Sensing
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• v.23 no.6
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• pp.493-500
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• 2007

In general, it accomplished a spectral reflectance analysis to be, the measurement results appear differently by targets, methods and condition. This paper presents a standard methodology for preprocessing mineral/rock samples and setting the distance from a target to the sensor, and then examines closely the spectral features for pyrophyllite. The size of mineral/rock samples is various according to the condition and scale of outcrop, so it is important to maintain the distance between the sensor and the sample. Before standardization for preprocessing samples and the sensor and sample distance, we prepare various rock samples (Quartz Porphyry) such as natural rock, pebble, powder and cutting rock. For a qualitative analysis to minimize the effect of surface condition of the sample and shadow, we maintains the distance from the sample to the sensor at 30cm and measures three times repeatedly for cutting the sample at $1{\sim}2cm$ thickness. To illustrate the proposed methodology, a case study for pyrophyllite was carried out. In this study, pyrophyllite showed an absorption pattern at wave length of 1.406nm, 1,868nm, 2.180nm and 2.309nm, and a higher grade represented strong absorption at 1.406nm and 2.180 nm. These absorption feature corresponds the band 7 of LANDSAT TM and band 8 of ASTER imageries. So, using these results, pyrophyllite deposits were extracted from other features (such as barren area, concrete area, bed of river, stone pit area etc.).

• The Journal of the Petrological Society of Korea
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• v.27 no.4
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• pp.195-205
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• 2018

Noerok is a green pigment made of mineral used the Gachil(priming coat) of wooden architecture in Chosun Dynasty era. It has been reported that various Noerok are discovered in Janggimyeon, Pohang. In this study, The Noerok from two places is compared and discussed. Noerok in the two places has blulsh-green to green color, and it is similar to their occurrences on fracture filling, vein and dike on outcrop. However, there are differences between two sites according to its petrological feature, mineral composition and geochemistry. While the Noeseongsan sample is mostly celadonite, Gwangjeongsan samples are characterized by celadonite with varying contents of cristobalite, tridymite, feldspar, along with some vitrified contents. In terms of major elements, the amount of $Al_2O_3$, $Fe_2O_3$, MgO and $K_2O$ decreases linearly with increasing $SiO_2$, whereas $Fe_2O_3$ is linearly proportional to MgO. In summary, Noerok in the study areas can be classified into 4 types (type 1, type 2, type 3-1, type 3-2) base on color, mineral composition, elemental composition, and vitrification grade.

• Geophysics and Geophysical Exploration
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• v.22 no.3
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• pp.149-159
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• 2019

Borehole elemental concentration logging, measuring neutron-induced gamma rays by inelastic scattering and neutron capture interactions between neutron and formation, delivers concentrations of the most common elements found in the minerals and fluids of subsurface formation. X-ray diffraction and X-ray fluorescence analysis from core samples are traditionally used to understand formation composition and mineralogy, but it represents only part of formations. Additionally, it is difficult to obtain elemental analysis over the whole intervals because of poor core recovery zones such as fractures or sand layers mainly responsible for groundwater flow. The development of borehole technique for in situ elemental analysis plays a key role in assessing subsurface environment. Although this technology has advanced consistently starting from conventional and unconventional resources evaluation, it has been considered as exclusive techniques of some major service company. As regards domestic research and development, it has still remained an unexplored field because of some barriers such as the deficiency of detailed information on tools and calibration facility for chemistry and mineralogy database. This article reviews the basic theory of spectroscopy measurements, system configuration, calibration facility, and current status. In addition, this article introduces the domestic researches and self-development status on borehole elemental concentration tools.

• Korean Journal of Crystallography
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• v.1 no.1
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• pp.35-48
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• 1990

본 연구에서는 포항-연일지역 및 감포-하서지 역의 점토광물과 주변모암의 열괭창 특성, 지구화 학적 및 물리적 특성. 그리고 성인에 대하여 고찰하였다. Ca계 몬모릴로나이트영역에 속함을 알 수 있다. 그러나 제올라이트는 뚜렷한 특징을 보이지 않는다. 점토질암석과 그 이외의 벤토나이트 및 제올라이트사이의 Sr. Cu, V. Li과 La의 함량에는 차이가 발견된다.