• The Journal of the Petrological Society of Korea
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• v.26 no.4
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• pp.361-371
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• 2017

We investigated geochemical characteristics of the Dodong Basaltic Rocks in the lower part of the Ulleung Island. They have lithological range of alkali basalt to trachybasalt, belonging to Na and K subseries of alkaline series. They mostly fall within the field of alkalline within-plate basalts on tectonic discrimination diagrams, and then plot in the field of oceanic island basalt (OIB). Geochemically, extension of lithospheric mantle and asthenospheric upwelling after East Sea under an Cenozoic extensional tectonic setting might be a heat source for partial melting of the enriched lithospheric mantle, which might generate the basaltic magma. But we cannot exclude that mantle plume might also be a heat source for melting of the lithospheric mantle.

• The Journal of the Petrological Society of Korea
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• v.17 no.1
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• pp.36-43
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• 2008

Many plutonic rock fragments of granitic composition were collected from the Deception Island. We obtained K-Ar ages of $62.5{\pm}1.2\;Ma$ and $140.7{\pm}2.7\;Ma$ from the two samples. Such result contradicts the general belief that most of the volcanic rocks of Deception Island are products of very recent activities and their maximum age does not exceed 200 ka. On the other hand, Mesozoic to Cenozoic rocks produced by subduction-related active magmatism have been reported from both South Shetland Islands and Antarctic Peninsula, located to the north and south of the Deception Island respectively. Also, various kinds of plutonic rocks with granitic composition are distributed widely. Therefore, plutonic rock fragments with granitic composition discovered from the Deception Island seem to indicate their derivation by capturing granitic crustal material underlying volcanic edifice during the volcanic activities, instead of differentiation from magmas related with recent volcanism. Ages and rock types of the plutonic rock fragments suggest arc-related origin just as adjacent South Shetland Islands and Antarctic Peninasula.

• The Journal of Engineering Geology
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• v.2 no.1
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• pp.70-91
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• 1992

Cheju and Oahu island are similar in geology, characterized by same types of volcanic activities during the late Tertiary to the early Quaternary. The occurrence of groundwater in both islands depend on two basic elements, permeability of volcanic rocks and precipitation. However, groundwater occurrence in Oahu is much more controlled by dike complex in the regional volcanic rocks. There are two different types of groundwater in both islands. One is perched groundwater standing at any high altitude, and the other is basal groundwater developed near the coastal area. The groundwater quality of Cheju island is good in general for drinking. But many wells near the eastern coastal area are salt intruded due to over pumping activities and the area of salt water intrusion has increased landward from the year of 1970. This feature of salt water contamination is similar at Pearl Harbour in Oahu island. In order to prevent this salt water contamination into fresh groundwater reservoir on Cheju island, it is urgently asked to make groundwater flow study along the coastal area on terms of groundwater potentials and their maximum ultimate exploration.

• Journal of the speleological society of Korea
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• v.42 no.2
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• pp.17-28
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• 1995

THE K-AR METHOD of age determination is commonly used to date rocks from Pleistocene volcanoes in Japan (e.g. Kaneoka et al. 1980, Itaya et al. 1984, Shimizu et al. 1988, Itaya et al. 1989). However. there are still many problems with K-Ar dating of the young volcanic rocks, as reviewed by Itaya and Nagao (1988).(omitted)

• Journal of the Korean earth science society
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• v.38 no.2
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• pp.141-149
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• 2017

The geology of Saok island area in Jeollanam-do can be divided into 4 lithologic types: Jurassic granite, Cretaceous sedimentary rocks, acidic tuff and acidic dikes. In the Saok island area, dinosaur and web-footed bird footprints, arthropod trackway and silicified wood were found recently in the Cretaceous sedimentary rocks which composed of alternating light grey sandstone, shale and mudrock. The fossil-bearing sedimentary rock is overlain by an acidic tuff, and the sedimentary rock and acidic tuff are cut by acidic dykes. In order to constrain the depositional age of the Cretaceous sedimentary rocks in Saok island area, SHRIMP U-Pb zircon ages were determined in the tuffaceous sandstone and overlying acidic tuff. Zircon U-Pb ages of the sandstone and tuff are $83.58{\pm}0.86$ and $79.80{\pm}0.75Ma$, respectively, which belong to the Campanian of the Late Cretaceous. The U-Pb age of the acidic tuff indicates the eruption time of acidic tuff and thus the minimum age of the fossil-bearing sedimentary rocks in this area. Therefore, the formation age of the dinosaur and web-footed bird footprints can be constrained between 83.6 and 79.8 Ma.

• Economic and Environmental Geology
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• v.19 no.2
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• pp.153-163
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• 1986

Paleomagnetic and geological studies of volcanic and sedimentary rocks of Jeju Island have been carried out to determine the position of virtual geomagnetic pole(VGP), and to estimate the geological sequence and their age. As a result of paleomagnetic studies, the reversal polarities are measured in the Sanbangsan trachyte and Hwasun formation, and the normal are the rest. In case of normal polarity, the mean values of declination and inclination are $2.3^{\circ}$ and $48.4^{\circ}$, respectively, and the average value of VGP is $85.4^{\circ}N$ and $79.9^{\circ}W$. The locations of VGP's are coincident with those obtained from world-wide Plio-Pleistocene rocks. The Hwasun formation and Seongsan formation which have been known to be sedimented in the similar time in the 2nd-stage of volcanic eruption, possess reversal and normal polarities, respectively. This fact brings about the result that two formations should be separated in a sense of geological sequence. Consequently, the geological sequence of the 2nd-stage of volcanic eruption is Pyoseonri basalt-Seoguipo hawaiite-Hwasun formation-Seongsan formation-Jungmun hawaiite-Sanbangsan trachyte. Referring to the paleomagnetic studies and the previous and present geological studies, Seoguipo formation corresponds to the Gauss normal epoch, the 2nd-stage of volcanic eruption to Matuyama reversed epoch, and the 3rd-, 4th-, and 5th-stages to Brunhes normal epoch. Therefore, the Seoguipo formation is mostly sedimented during late Pliocene and/or presumably extended to the early Pleistocene. The rocks of the 2nd- to 5th-stage are formed later than this.

• The Journal of the Petrological Society of Korea
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• v.2 no.2
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• pp.139-155
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• 1993

We have shown that the volcanic rocks from the northern part of Cheju Island can be divided into high $P_2O_5/K_2O$(HPK) and low $P_3O_5/K_2O$(LPK) groups, each with distinct geochemical characteristics(Park and Kwon, 1993a and b). This study reports mineral compositions for plagioc-lase, olivine, and clinopyroxene in order to see the dependence of mineral chemistry on the whole rock composition, and discusses equilibrium relationships between crystal and liquid. Plagioclase and olivine phenocrysts show no compositional differences for the two rock group. However, $Al^{ⅵ}/Al^{ⅳ}$ ratios of clinopyroxenes suggest that pyroxenes have fractionated at deeper level, and that the LPK group might have fractionated at higher pressure than the HPK group. These are in good agreement with our previous interpretation based on whole rock chemistry(Park and Kwon, 1993a). Although subhedral or euhedral form and homogenous composition for most plagioclase and clinopy-roxene phenocrysts suggest equilibrium relationship with liquid, the uncertainties associated with liquid, the uncertainites associated with equilibrium constant for these minerals do not allow testing equilibium relationship between mineral and liquid on the basis of chemistry. On the other hand, olivine phenocrysts in hawaiites, for which Kd is well known, show distinct nonequilibrium relationship with calculated liquid composi-tions, while those in other rock compositions are in equilibrium from those for other rocks. We report for the first time as far as we know plagioclase xenocryst and pigeonite inclusion in plagioclase, which indicates assimilation process. In conclusion, these mineralogical observations imply that mag-matic processes underneath the Cheju volcano were not simple.

• Journal of Plant Biology
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• v.32 no.4
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• pp.363-373
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• 1989

Morphotaxonomic accounts are given to four species of Amphiroa, Rhodophyta from Cheju Island ; A. valonioides Yendo, A. itonoi Srimanobhas et Masaki, A. rigida Lamouroux, and A. misakiensis Yendo. A. valomioides has one-tiered genicula of unequal length and its semiendophytic in other Amphiroan species, whereas A. rigida has two-tiered genicula of equal length and is semi-endophytic in non-articulated coralline alga. A misakiensis has five to thirteen-tiered genicula of unequal length and forms tufts on rocks where the branches are often recumbent. A. rigida is introduced for the first time to Korean flora.

• Journal of the speleological society of Korea
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• no.5
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• pp.56-65
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• 1997

The cavernous rocks of New Zealand can be grouped broadly into two main geologic types-the massive, metamorphosed, Ordovician, Mt. Arthour Marble of north-west South Island, and the stratified, bioclastic, Tertiary Te Kuiti limestones of western regions of both islands. Although much cave exploration has been carried out in both these regions, the principal study so far has involved caves and karst in the central western portion of North Island near the well-known Waitomo Caves, where some 85km of caves have been surveyed during the past 12 years by members of New Zealand Speleolgical Society.

• Economic and Environmental Geology
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• v.24 no.3
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• pp.277-285
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• 1991

We applied Sm-Nd isotopic system to so-called amphibolites occurring within the Ogcheon group to provide constraints on the age of the metasedimentary rocks and to characterize tectonic environment of basaltic magmatism. An internal mineral isochron age of $677{\pm}91Ma({\sigma})$ was obtained from a coarse-grained, intrusive, amphibolite near Mungyeong. Considering previous studies on the age of the Ogcheon group, we interpret that the isochron represents either early metamorphic or emplacement age. The depositional age of the metasedimentary rocks intruded by the amphibolite would be prior to late Proterozoic. The present study and Cambro-Ordovician fossil evidences of previous workers suggest that both Precambrian and Phanerozoic rocks are present in the Ogcheon group. Positive ${\varepsilon}$ Nd values(+2.4 to +3.5) of four whole rocks indicate mantle origin for the amphibolite. These isotopic data, along with published immobile trace element data of Cluzel et al.(1989), strongly suggest that parental rocks of the amphibolite formed in an intraplate environment rather than in island arc or midocean ridge. The age and tectonic environment of amphibolites in the Ogcheon belt suggest that the basaltic magmatism may be related to the late Proterozoic break-up of a presumed supercontinent, but not to the Triassic(?) collision between North and South China continents.