• The Journal of Engineering Geology
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• v.1 no.1
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• pp.19-37
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• 1991

The geology of the northwestern Cheju Island consist of Pleistocene to Holocene volcanic rocks which could be devided into basalt layers, the Sungsan Formation composed mainly of volcaniclastic debris exposed along the shoreline, and more than 30 cinder cones. Columnar joints and vesicles are dominant in the basalts of the Pyeosunri and the Sihungri basalt Formations. Volcaniclast and clay layers are intercalated in basaltic layers. When volcaniclast of the interlayers would be swept away by ground water and some caves of channel shape would be formaed. Overlying lavas cracked by columnar joints could be easily destroyed, collapsed and/or sunk. Geomechananical nature of the rocks such as strength may be controlled by the vesicularity(size, shape, and orientation of the vesicles) of the rocks. On the basis of vesicularity as a factor of strength, the effective strength ratio(Ke) could be calculated as Ke=0.3-0.72, in which the smaller Ke value reflects the lower in internal stress. In the studied area, the strength of the rocks tends to decrease as increasing in altitude of provenance of the rocks. The rocks in the area show relatively low values in angle of failure strength($\phi$) ranging from 10$^{\circ}$ to 30$^{\circ}$. In conclnsion, the rocks in question, majority of which the critical value exceeds 0.33, belong to the unstable rocks in the aspect of engineering geology.

• The Journal of Engineering Geology
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• v.28 no.4
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• pp.619-630
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• 2018

The purpose of this study is to investigate the existence of faults and intrusive rocks in the volcanic rock mass of Ulleung-do using magnetic anomalies. The magnetic survey data show that basaltic (mafic) rocks have high magnetic anomalies and that trachytic (felsic) rocks have low magnetic anomalies, implying that the anomaly distributions can be used to distinguish between different volcanic rock types that may be covered by regolith (such as alluvial and colluvial deposits) and other sedimentary layers. Our results show that basaltic rocks are not present within the Nari caldera. However, outside the caldera, the occurrence of high magnetic anomaly values of >$1,000{\gamma}$ is presumed to reflect the existence of basaltic craters or volcanic vents that formed prior to the eruption of the trachytic rocks. In particular, the area with anomaly values of >$1,000{\gamma}$ in the vicinity of Namyang-ri, southwest of Ulleung-do, is interpreted as having a high probability of hosting a crater and vent originating from mafic volcanism.

• The Journal of the Petrological Society of Korea
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• v.27 no.3
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• pp.153-171
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• 2018

This study focuses on the investigation of geologic distribution and stratigraphy in the eastern part of Yeongdeok-gun, based on Lidar imaging, detailed field survey, microscopic observations, SHRIMP and LA-MC-ICPMS U-Pb age dating, and a new geological map has been created. The stratigraphy of the study area is composed of the Paleoproterozoic metamorphic rocks consisting of banded gneisses of sedimentary origin and schists ($1841.5{\pm}9.6Ma$) of volcanic origin, Triassic Yeongdeok plutonic rocks ($249.1{\pm}2.3Ma$) and Pinkish granites ($242.4{\pm}2.4Ma$), Jurassic Changpo plutonic rocks ($193.2{\pm}1.9Ma{\sim}188.8{\pm}2.0Ma$) and Fine-grained granites ($192.9{\pm}1.7Ma$), Formations [Gyeongjeongdong Fm, Ullyeonsan Fm. (~108 Ma), Donghwachi Fm.] of the Early Cretaceous Gyeongsang Supergroup and acidic volcanic rocks and dykes erupted and intruded in the Late Cretaceous, Miocene intrusive rhyolitic tuffs ($23.1{\pm}0.2Ma{\sim}22.97{\pm}0.13Ma$) and sedimentary rocks of the Yeonghae basin, and the Quaternary sediments. The Triassic Pinkish granites, Jurassic Changpo plutonic rocks and Fine-grained granites are newly defined plutonic rocks in this study. Miocene intrusive rhyolitic tuffs bounded by the Yangsan Fault, which was first discovered in the north of Pohang city, are believed to play an important role in the understanding of the Miocene volcanic activity and the crustal deformation history on the Korean Peninsula. It is confirmed that The NNE-SSW-striking Yangsan Fault penetrating the central part of the study area and branch faults are predominant in the dextral movement and cutting all strata except the Quaternary sediments.

• Journal of the Korean earth science society
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• v.45 no.2
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• pp.136-146
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• 2024

This paper introduces the seismic facies classification and mapping of igneous bodies found in the sedimentary sequences of the Yellow Sea shelf area of Korea. In the research area, six extrusive and three intrusive types of igneous bodies were found in the Late Cretaceous, Eocene, Early Miocene, and Quaternary sedimentary sequences of the northeastern, southwestern and southeastern sags of the Gunsan Basin. Extrusive igneous bodies include the following six facies: (1) monogenetic volcano (E.mono) showing cone-shape external geometry with height less than 200 m, which may have originated from a single monogenetic eruption; (2) complex volcano (E.comp) marked by clustered monogenetic cones with height less than 500 m; (3) stratovolcano (E.strato) referring to internally stratified lofty volcanic edifices with height greater than 1 km and diameter more than 15 km; (4) fissure volcanics (E.fissure) marked by high-amplitude and discontinuous reflectors in association with normal faults that cut the acoustic basement; (5) maar-diatreme (E.maar) referring to gentle-sloped low-profile volcanic edifices with less than 2 km-wide vent-shape zones inside; and (6) hydrothermal vents (E.vent) marked by upright pipe-shape or funnel-shape structures disturbing sedimentary sequence with diameter less than 2 km. Intrusive igneous bodies include the following three facies: (1) dike and sill (I.dike/sill) showing variable horizontal, step-wise, or saucer-shaped intrusive geometries; (2) stock (I.stock) marked by pillar- or horn-shaped bodies with a kilometer-wide intrusion diameter; and (3) batholith and laccoliths (I.batho/lac) which refer to gigantic intrusive bodies that broadly deformed the overlying sedimentary sequence.

• Economic and Environmental Geology
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• v.38 no.2 s.171
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• pp.143-153
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• 2005

Euiseong subbasin, included in the Kyungsang Basin, was created by the result of volcanic activity in the late Cretaceous, and contacts with Milyang and Youngyang subbasins by Palgongsan and Andong faults, respectively. In this study, geophysical survey is implemented fur investigating surface and subsurface geologic structure in Euiseong subbasin which composed with the complex of volcanic and plutonic rocks. To understand surface geologic feature, IRS satellite image and DEM(Digital Terrain Map) are used for analyzing lineament and its density. The numbers of lineaments show major trend in $N55^{\circ}\~65^{\circ}W$, and aspects of lineament lengths show major trend in $N55^{\circ}\~65^{\circ}W$ and N-S directions. 13 delineate subsurface density discontinuity; Power spectrum analysis was implemented for gravity anomaly data, resulting $4-5{\cal}km$ depth of basin basement and $0.5-0.6{\cal}km$ depth of shallow discontinuity. From the result of power spectrum analysis, 2.5-D modelings were implemented along two profiles of A-A' and B-B', and they show subsurface geology in detail. Analytic signal method for detecting boundaries of magnetic basements show 0.001-130 nT/m values, and high energy area show good correspondency with the boundaries of Palgongsan granite and caldera areas in Euiseong subbasin.

• Journal of the Korean Geophysical Society
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• v.3 no.2
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• pp.77-90
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• 2000

Five electrical resistivity dipole-dipole and two seismic reflection surveys were performed in the southeastern margin of the Yongdong basin to delineate the shallow basin architecture. To investigate the intra-basin structure, twenty four resistivity sounding points and three dipole-dipole lines were selected especially in the vicinity of volcanic masses. The basin-fault boundaries are identified in electrical dipole-dipole resistivity section as high resistivity-contrast of approximately $1,500\;{\Omega}{\cdot}m$, characterized as a band of high standard-deviation. They are also effectively clarified in the seismic reflection data: amplitude and continuity contrasts in the common shot gather, first-arrival profiles, complex attribute plots. The intra-basin resistivity structures are constructed by interpolating vertical electrical sounding data and dipole-dipole profiles. The high-resistivity anomalies most likely originate from the northsouth-trending and northeast-dipping volcanic masses, which are to be further quantitatively investigated with geomagnetic and magnetotelluric surveys.

• Journal of the Korean Geophysical Society
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• v.2 no.3
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• pp.201-208
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• 1999

A high-resolution seismic profile acquired across the middle part of the Pungam Basin, one of the Cretaceous sedimentary basins in Korea, has been interpreted to delineate subsurface geological structures. Boundary faults, intrusive bodies, and unconformity surfaces are identified on the seismic section. Basin fills are divided into five depositional units (Units I, II, III, IV, and V in descending order). The normal faults were formed by transtentional movement along a sinistral strike-slip fault zone. Unconsolidated sediments, a weathered layer, and sedimentary layers overly the Precambrian gneiss. The granite body intruded at the southeastern part contacts the adjacent sedimentary rocks by a near-vertical fault. Granitic intrusions caused tectonic fractures and normal faults of various sizes. An andesitic intrusive body indicates post-depositional magmatic intrusions. Continuous strike-slip movements have deformed basin-filling sediments (Units I and II).

• The Journal of the Petrological Society of Korea
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• v.24 no.1
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• pp.1-10
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• 2015

Neulgeori prehistoric site is located at Joong-ri Kwanin-myon Pocheon-si, Gyeonggi-do, where lots of stone artefacts were excavated. We investigated the petrological features of the artefacts through petrographical observation and modal analysis. In addition we estimated the provenance of the artefacts by means of the geological survey. The twelve stone artefacts used in this study are identified as ash tuff, lapilli tuff, granite porphyry, andesite and diorite porphyry. Various rocks were used for making flakes, whereas blades and debris were from the tuffaceous rocks. Lapilli tuff is considered to have been delivered from the Dongmakgol tuff in the Cheolwon basin, granite porphyry from the Cretaceous granite porphyry stocks cropped out at the southeastern Oksan-ri and eastern Yeoncheon areas. Andesite artefact would have been originated from the outcrops located at the northern part of the site, and diorite porphyry artefact from the southern part of the site. The stone artefacts investigated are estimated to have been transported from the area within 15 kilometers from the site.

• Journal of the Korean earth science society
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• v.30 no.7
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• pp.801-809
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• 2009

The Salinas Grandes borate deposit located in Jujuy state, northern Argentina can be categorized into the playatype evaporite deposit. Major borate mineral is ulexite ($NaCaB_5O_9{\cdot}H_2O$), which boron could be originated from volcanic rocks nearby playa. The eastern part of the Jujuy state in northern Argentina belongs to the Altiplano-Puna platform which shows high altitude and semiarid climate. Lots of Mesozoic and Cenozoic volcanics that are source of boron as well as playas that are the basin for borate precipitation in the area are essential for boron evaporite deposit. Therefore, the extensive explorations for the playa-type evaporite deposit are need.

• Journal of the Korean earth science society
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• v.38 no.1
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• pp.49-63
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• 2017

The geochemical results of the Chunyang granites located in the northeastern part of the Yeongnam Massif, indicate that these rocks have characteristics of calc-alkaline series in the sub-alkaline field, I-type and peraluminous. Most of the geochemical features in major and trace elements show systematic trends, which are similar to differentiation trends of the general Jurassic granitoids in South Korea. The Chunyang granite is largely enriched in mobile LILE (Sr, K, Rb and Ba) relatively immobile HFSE. They show LREE enriched patterns [$(La/Lu)_{CN}=41.8-73.2$] with a slightly negative Eu anomaly [$(Eu/Eu^*)_{CN}=0.89-1.10$]. There are no meaningful correlations in major and trace elements between the Chunyang granites and the Buseok plutonic rock which is the main unit of the Yeongju batholith. This result may suggest that these two plutonic rocks be not derived from the same parent magma. Tectonic discrimination diagrams indicate that the Chunyang granite was formed in volcanic arc environments. These geochemical characteristics results suggest that the Chunyang granite must have been generated at the active continental margin during the subduction of the Jurassic proto-Pacific plate.