• Economic and Environmental Geology
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• v.33 no.3
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• pp.173-180
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• 2000

Main aims of this study are to clarify petrochemistry of the granitic gneiss in the Durye-Suncheon area. The origin of the metamorphic rock is evaluated from the abundance of $Na_2O$, the $TiO_2$/$Al_2O_3$ratios, the Harker variation diagram and $Al_2O_3$($Na_2O$ +$K_2O$ + CaO) ratios of the major elements. and the frequency distribution and average abundance of the trace elements . The trace elements of the granitic gneiss in the studied area are compared with those of the granitic rocks with shales in the other areas. The abundance of $Na_2O$ is lower than 3.27% and the $TiO_2$/$Al_2O_3$ ratio is 0.04. Also the Harker's variation diagram indicate this granitic gneiss correspond to sedimentary origin or S-type granite. The average abundance for trace elements of the granitic gneiss is similar to that of the shale, and the frequency distribution shows extensive distribution and irregularly . But xenolith are observed in the field survey, it is evidence of igneous origin , and then origin of the granitic gneiss in studied area is S-type granite.

• Economic and Environmental Geology
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• v.28 no.5
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• pp.513-518
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• 1995

A granite drilling core (-1200 m) obtained near the Majang cave in east part of the Cheju island. The rock is pinksh in color and has miarolitic cavities. It is coarse-grained rock and consists of quartz, plagioclase, alkali feldspar, biotite and magnetite. The rock shows characteristically micrographic texture. The alkali feldspar is subhedral to anhedral and generally interstitial grains and fonns micrographic texture. K/Ar age of alkali feldspar in the core specimen is $58.14{\pm}1.4Ma $ (early Tertiary). The age, rock features and whole rock chemistry of the rock has strong resemblance to micrographic granites, so called "masanite", in southeastern part of the Korean peninsular. The granitic fragments from drilling core (- 920 m) obtained in Jungmun area in south part of the Cheju island consist of quartz, plagioclase, alkali feldspar and biotite. The fragments in the Jungmun area are similar to granitic xenolith near the Cheju city for the absence of micrographic texture and different alkali feldspar.

• Economic and Environmental Geology
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• v.26 no.3
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• pp.349-361
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• 1993

The granitic rocks in the study area are divided into the schist and gneiss complex, Yongdok pluton, Yonghae pluton and Onjong pluton by their texture, fabric and relationship to the adjacent rocks in the field, Schist and gneiss complex occurs as xenolith or roof pendant in the Yongdok, Yonghae and Onjong plutons. The Yongdok pluton occurs in association with pegmatite and aplite in many places of its pluton. In the field it is obviously clarified that the Yongdok pluton is unconformably overlay by the Cretaceous sedimentary rocks. The Yonghae and Onjong plutons are gradationally changed each other, and these plutons truncate both the Yongdok pluton and the Cretaceous sedimentary rocks. Petrographically, the Yongdok pluton consists of granodiorite and granite with minor quartz monzonite. The Yonghae pluton is composed of diorite, quartz diorite, tonalite, and granodiorite. The Onjong pluton also ranges granodiorite to granite. Both the Yongdok and Yonghae-Onjong plutons are different in the constituent minerals, such as alkali feld~par, myrmekite, mica, sphene and mafic minerals. This suggests that each pluton might have been different crystallization sequence and characteristically different gological history during the crystallization period. Iron/magnesium ratio in biotite and hornblende from both the Yongdok and Yonghae-Onjong plutons gradually decrease as the differentiation index increasing in the whole rock. The decrease of this ratio strongly depend on the increase of opaque mineral contents. From the results of chemistry in the whole rocks and some mafic minerals, it is suggest that the granite plutons of the two different geological ages would have been suffered the environment of high oxygen fugacity in the process of magmatic emplacement and during the crystallization period.

• The Journal of the Petrological Society of Korea
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• v.16 no.4
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• pp.196-207
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• 2007

Miocene basalt plugs in Goseong contain a large variety of crustal and mantle xenoliths and xenocrysts. One of basalt plugs, Unbongsan, are derived from 160 km depth. Whole-rock geochemistry and pressure and temperature conditions of mineral phases indicate that Unbongsan volcanic rocks are alkali basalts and the source magma of the alkali basalts was generated from about $0.2{\sim}2%$ partial melting of depleted garnet peridotite. Crystallization pressures and temperatures of mineral phases within ascending magma of Unbongsan alkali basalt indicate that olivines, clinopyroxenes, and plagioclases were crystallized at $75{\sim}110km,\;40{\sim}52km,\;37{\sim}54km$ depth, respectively. The ascending magma of Unbongsan alkali basalts enclosed mantle xenoliths at about $57{\sim}67km$ depth.

• Proceedings of the Mineralogical Society of Korea Conference
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• 2000.05a
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• pp.19-19
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• 2000

;Ultramafic xenoliths found in alkali basalts from Jeju-do, Korea are mostly spinel Iherzolites composed of olivine, orthopyroxene, clinopyroxene and spinel. A subordinate amount of spinel harzburgites and pyroxenites are also found. Temperatures for these xenoliths were estimated from the compositions of coexisting pyroxenes (Wood '||'&'||' Banno 1973; Wells 1977; Bertrand '||'&'||' Mercier 1985; Brey '||'&'||' Kohler 1990), the AI-solubility in orthopyroxene coexisting with olivine and spinel (Sachtleben '||'&'||' Seck 1981; Webb '||'&'||' Wood 1986), and from Fe/Mg partitioning between olivine and spinel (Ballhaus et al. 1991). Temperature estimates from the thermometers by Wells (1977) and Brey and Kohler (1990) are compatible. Average equilibrium temperatures by these two methods for spinel peridotites range from 890 to 1030$^{\circ}$C. Pressures for spinel peridotites were estimated from the geobarometer by Kohler and Brey (1991) derived from the equilibrium Ca content of olivine coexisting with clinopyroxene, and fall within the range of 12.9 to 26.3 kbar. The combination of the thermometer by Brey and Kohler (1990) and the geobarometer by Kohler and Brey (1991) yields P- T estimates for Jeju-do spinel peridotites that fall in experimentally determined spinel lherzolite field in CFMASCr system (O'Neill 1981). These P-T data sets have been used to construct the Quaternary Jeju-do geotherm, which is significantly different from the conventional conductive geotherm. The xenolith-derived geotherm has a higher T gradient at low P (13 kbar) than at high P, which may be due to perturbation of the conductive heat flow by magma underplating or overplating at the crust-mantle boundary. Temperature estimates and statistics on the xenoliths indicate that the crust/mantle boundary in Jeju-do lies at about 11 kbar (~39 km). Spinellherzolite is inferred as a main constituent rock of the uppermost lithospheric mantle beneath Jeju-do. Pyroxenites were intercalated in peridotites in similar depth and temperature as re-equilibrated veins or lens.

• Journal of the Mineralogical Society of Korea
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• v.21 no.4
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• pp.373-382
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• 2008

First reported geochemical characteristics of mantle xneoliths (spinel peridotites) from Sunheul-ri, Jeju Island, provide important clues for understanding the lithosphere composition, equilibrium temperature, and the period of entrainment and transport of the xenoliths in the host magma. Core and rim of mineral phases in the xenoliths are constant chemical compositions as $Fo_{89-90}$ of olivines. The ranges of equilibrium temperature, obtained by two pyroxenes geothermometer, are about $951{\sim}1035^{\circ}C$ for Sunheul-ri spinel peridotite xenoliths and are similar to the range of equilibrium temperatures for the xenoliths from other sites in Jeju island. The period of entrainment and transport of the xenoliths in the host magma of Sunheul-ri mantle xenoliths is about 42 days.

• The Journal of the Petrological Society of Korea
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• v.1 no.1
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• pp.34-41
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• 1992

The Precambrian granitic gneisses are widely distributed in the Danyang-Yecheon area, eastern part of Korea, where the Ryeongnam massif borders the Ogcheon fold belt. They are composed of migmatitic, biotite granitic, garnet-bearing and granoblastic granitic gneisses. The common joint sets of the granitic gneiss are NE and NS directions, which are probably related to the effects of Daebo orogeny and Bulgugsa disturbance, respectively. Mineral assemblages of the banded gneiss xenolith in the garnet-bearing granitic gneiss are quartz-plagioc1ase-biotite-mus-covite-orthoclase and quartz-plagioc1ase-biotite-garnet, belonging to the amphibolite facies. The granoblastic granitic gneiss is felsic, metaluminous, and granitic, and shows subalkaline trend. The garnet-biotite geothermometry of garnet-bearing granitic gneiss yields 640$^{\circ}$-708$^{\circ}C$ at pressure of 4 kb.

• Journal of The Geomorphological Association of Korea
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• v.18 no.3
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• pp.1-10
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• 2011

Sanbangsan and Yongmuri Beach as geosites are very wide areas, and tourists have accessed them via various courses; hence the need to double the number of geosite signs and disperse them at each point. The signs should read "Sanbangsan lava dome," "Yongmuri tuff ring," and "Relationship between the Sanbangsan lava dome and Yongmuri tuff ring." The contents of the sign should be systemic, simple, and clear because tourists have to read it in a short time. The viewpoint of the research area can be largely divided into Sanbangsan View, Yongmuri Beach View, Sanbangsan, and Yongmuri Beach View. Three of each viewpoint (total of 9 viewpoints) can be placed. In the geosite of Sanbangsan and Yongmuri Beach are 5 sub-theme views including the boundary sheet of Sanbangsan and Yongmuri tuff ring, xenolith basalt, marine pothole, tafoni, and crossed sedimentary layer. These sub-theme views are important in understating not only the geosite but the overall geopark as well, so they should be developed and utilized aggressively.

• Journal of the Korean earth science society
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• v.44 no.6
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• pp.611-628
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• 2023

This study aimed to explore the geo-educational value of Deokmyeong-ri in Goseong-gun, Gyeongsangnamdo, through field research. The study area comprises well-exposed outcrops, which can be used as field sites during field trip for studying sedimentary structures (normal grading bedding, cross bedding, ripple, and desiccation crack), coastal depositional environments (coastal cliff, shore platform, and gravel beach), basic principles of relative dating (unconformity, fault, intrusion, and xenolith), and columnar joints. This study evaluated the field sites based on the achievement standards and textbooks used in the science curriculum. The field sites have a high educational value because they exhibit typicality, as mentioned in the textbook, and provide study materials for enrichment learning. Furthermore, Deokmyeong-ri Area has well-developed tourist and educational infrastructures; thus, it is a safe place for geological education.

• The Journal of the Petrological Society of Korea
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• v.11 no.3_4
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• pp.157-168
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• 2002

In Gimcheon area of the central Yeongnam massif granite gneiss occurrs with intercalated biotite gneiss at xenolith or restite. In order to understand the evolution of the central Yeongnam massif, it is essential to have absolute age information, but not many age data are available yet. Furthermore the previous age determinations from the study area are not compatible with the outcrop relationship. In this study we determined chemical ages from the zircon grains. We obtained ages of $1970\pm$ 78(l$\sigma$)Ma from the granite gneiss, $1814\pm$77(l$\sigma$)Ma from the outer rim of a rounded zircon and 1973$\pm$97(l$\sigma$)Ma from a longish zircon, both from the biotite gneiss. These ages seem to indicate the timing of granitic magma intrusion and subsequent metamorphism. Ages of $2954\pm$ 158($l\sigma$)Ma, 2440$\pm$58(l$\sigma$)Ma, and 2219$\pm$36($l\sigma$)Ma obtained from zoned core of the rounded zircon grain from the biotite gneiss suggest various geological events before such metamorphism of the biotite gneiss. Ages in the range of 1450~1670 Ma observed in zircons of both gniesses suggest later metamorphism that the granite gneiss and the biotite gneiss experienced together. The chemical age determination by electron probe micro-analyzer of this study utilized 1$\mu\textrm{m}$ beam diameter and it seems to be a very useful age determination from the zircons with complex growth history because of superior spatial resolution.