• The Journal of the Petrological Society of Korea
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• v.16 no.2 s.48
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• pp.82-99
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• 2007

The Paleogene dikes intruding into the late Cretaceous granodiorite are pervasively observed in the Irun-myeon, eastern Geoje Island. They are classified into three groups: NW-trending acidic dike swarm and WNW- (A-Group) and $NS{\sim}NNE-trending$ (B-Group) basic dike swarms. Based on their cross-cutting relationships, the earliest is the acidic dike group and fellowed by A- and B-Groups in succession. The acidic dikes seem to have intruded into tension gashes induced by the sinistral strike-slip faulting of the Yangsan fault system during the late $Cretaceous{\sim}early$ Paleogene. In terms of rock-type, orientation, age, and geochemistry, A-Group and B-Group are intimately correlated with the intermediate and basic dike swarms in the Gyeongju-Gampo area, respectively. These results significantly suggest that the corresponding dike swarms are genetically related. Based on the K-Ar and Ar-Ar age data, A- and B- Groups were intruded during $64{\sim}52\;Ma$ and $51{\sim}44\;Ma$, respectively. The result means that the direction of tensional stress in and around the SE Korean peninsula was changed abruptly from NNE-SSW to $EW{\sim}WNW-ESE$ at about 51 Ma. Considering the tectonic environments during the Paleogene, it is interpreted that A-Group was injected along the WNW-trending tensional fractures developed under an regional sinistral simple shear regime which was caused by the north-northwestward oblique subduction of the Pacific plate beneath the Eurasian plate. Meanwhile, the regional stress caused by the collision of India and Eurasia continents at about 55 Ma was likely propagated to the East Asia at about 51 Ma, and then the East Asia including the Korean peninsula was extruded eastwards as a trench-rollback and the dip of downgoing slab of the Pacific plate was abruptly steepened. As a result, the strong suction-force along the plate boundary produced a tensional stress field trending EW or WNW-ESE in and around the Korean peninsula, which resultantly induced B-Group to intrude passively into the study area.

• The Journal of the Petrological Society of Korea
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• v.27 no.2
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• pp.73-84
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• 2018

In the northern Cheongsong, there are occurred igneous intrusions: Cheongsong dike swarm, Jungtaesan laccolith, Galpyeongji stock. The swarm is composed of rhyolitic dikes that have developed many various spherulites. The dikes represent an geometrically radical pattern centering the Galpyeongji stock, but also geochemistry of the intrusions indicate the swarm source. Here we report the compositional data for 28 samples from the three intrusions. All of the intrusions belong to rhyolitic composition, but according to compositional correlation, there are considerable overlaps between intrusion compositions. In particular, the Cheongsong dike swarm is divided into several dike groups by rock color and shows compositional diversity, but the composition of the dikes generally overlap with compositions of other intrusions. The Jungtaesan laccolith is enriched in alkali, $K_2O$ and $Al_2O_3$ and depleted in $Fe_2O_3{^t}$, $TiO_2$ and REE compared to the Cheongsong dike swarm. In contrast, the Galpyeongji stock is narrow in composition range, and commonly has sharp compositional overlaps with the Cheongsong dike swarm. According to the compositional correlations, the stock is considered to be a source of the swarm and it is connected to an episode of volcanism.

• The Journal of the Petrological Society of Korea
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• v.24 no.2
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• pp.91-105
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• 2015

Jungtaesan and Galpyeongji intrusions in the northeastern Cheongsong occur as laccolith and stock which intrude Gasongdong Formation and Dogyedong Formation, respectively. Cheongsong dike swarm, intruding the Dogyedong Formation, is closely associated with this stock. The dike swarm is more radial to focus into Galpyeongji and its outline is oval. The dikes of the dike swarm are only rhyolite dikes with flow banded, spherulitic and rare stony structures, and represents a single intrusive phase of magma. It can be interpretated that orientation of the dikes is controlled by stress states. Therefore, the dikes display a radial pattern through occupying vertical joints that have been generally attributed to radial fractures formed during doming of the sedimentary rocks by the intrusion of the Galpyeongji stock. The dike pattern could sufficiently account for dike injections into these joints.

• Journal of the Korean earth science society
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• v.43 no.5
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• pp.618-638
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• 2022

The Middle Jurassic granite dike swarm intruding into the Paleoproterozoic banded gneiss is pervasively observed in Ueumdo, Hwaseong City, mid-western Gyeonggi Massif. Based on their cross-cutting relationships in a representative outcrop, there are four dikes (UE-A, UE-C, UE-D, UE-E), and depending on the direction, there are three granite dike groups, which are NW- (UE-A dike), NW to WNW- (UE-C dike), and NE-trending (UE-D and UE-E dikes). These granite dikes are massive, medium-to coarse-grained biotite granites, and their relative ages observed in outcrops are in the order of UE-A, UE-D (=UE-E), and UE-C. The geometric analysis of the dikes indicates that the UE-A and UE-C dikes intrude under approximately NE-SW trending horizontal minimum stress fields. The UE-A dike, which showed a relatively low average SiO2 content by major element analysis, is a product of early magma differentiation compared to other dikes; therefore, it is consistent with the relative age of each dike. The ²⁰⁶Pb/²³⁸U weighted mean ages for each dike obtained from SHRIMP zircon U-Pb dating were calculated to be 167 Ma (UE-A), 164 Ma (UE-C), 167 Ma (UE-D), and 167 Ma (UE-E), respectively. The samples of the UE-A, UE-D, and UE-E dikes showed very similar ages. The UE-C dike shows the youngest age, which is consistent with the results of the relative age in the outcrops and major element analysis. Therefore, the granite dikes intruded into the Middle Jurassic (approximately 167 and 164 Ma), coinciding with those of the Gyeonggi Massif, where the Middle Jurassic plutons are geographically widely distributed. This result indicates that the wide occurrence of the Middle Jurassic plutons on the Gyeonggi Massif was formed as a result of igneous activity moving in the northwest direction with the shallower subduction angle of the subducting oceanic plate during the Jurassic.

• The Journal of the Petrological Society of Korea
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• v.11 no.3_4
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• pp.182-199
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• 2002

We attempted to show the evolution of the magma and the geochemical characteristics of dikes and dike swarms by using the petrographic and geochemical data from 287 dikes, SE Korea. The dikes can be divided into mafic, intermediate, and felsic dikes in the field. And each of them is subdivided into three groups, two groups, and two groups, respectively. The group (I) among the mafic dikes most pervasively occurs and are distributed in both sides of the Yeonil Tectonic Line (YIL), which petrographic and geochemical characteristics are the same. These facts thus, strongly support the results of the previous studies which showed that they were intruded contemporaneously and that YTL was a main tectonic line which restricted the crustal clockwise rotation during the Early Miocene. The geochemical characteristics are discriminated according to the seven groups divided petrographically. The mafic, intermediate and felsic dikes belong to basalt and basaltic andesite, andesite and facile, and rhyolite, respectively, and the magmas mostly belong to calc-alkaline series. The geochemical data indicate that there were the fractional crystallizations of olivine, clinopyroxene, and plagioclase in the mafic dikes. And the content of characteristic elements and tectonic discrimination diagrams show that the dikes were formed from the magma related to the subduction of plate and that the tectonic setting was related to orogenic volcanic arc.

• 한국지구과학회:학술대회논문집
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• 2002.02a
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• pp.34-34
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• 2002

• Proceedings of the Mineralogical Society of Korea Conference
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• 2002.05a
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• pp.48-50
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• 2002

• The Journal of the Petrological Society of Korea
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• v.14 no.2 s.40
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• pp.93-107
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• 2005

We determined $^{40}Ar/^{39}Ar$ ages of the Tertiary dike swarms and volcanic rocks distributed in the SE Korea where the most prevalent crustal-deformation and volcanism occurred during the period. In previous study, it was disclosed that the mafic dike swarms on both sides (east and west) of the Yeonil Tectonic Line (YTL) were originated from a same magma although they are consistently aligned with different intrusion directions of NS and NE, respectively. Ages of the mafic dike swarms of this study are $47.3\pm0.8Ma$ and $48.0\pm1.3Ma$, respectively and confirm such conclusion. These facts clarify that the YTL acted as a westernmost limit of the crustal deformation, especially clockwise crust-rotation, during the Miocene. Frequent occurrence of basic dikes indicate strongly that the southeastern part of the Korean Peninsula was under E-W extensional stress field at about 48 Ma, intimately related to the India-Asia collision and subsequent sudden change of the Pacific Plate motion. The ages of the uncommonly appearing intermediate and felsic dikes were determined as $55.9\pm1.5Ma$ and $53.0\pm1.0Ma$, respectively. Ages of the andesitic lava of the Hyodongri Volcanics, the dacitic lava of the Yongdongri Tuff, and dacitic rocks intruding and covering the Churyeong Breccia were determined as $24.0\pm0.5Ma,\;21.6\pm0.4Ma$, $21.8\pm0.1Ma,\;and\;22.0\pm0.5Ma$ respectively. The ages from the volcanics agrees well with the stratigraphy established by the latest field survey, which confirms that the $andesitic\~dacitic$ volcanism was followed by the basaltic volcanism during the Early Miocene.

• The Journal of the Petrological Society of Korea
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• v.11 no.3_4
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• pp.169-181
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• 2002

Basic~intermediate dike swarms are pervasively developed in the east of the Ulsan Fault, SE Korea. Most of them intruded initially along the NS-trending extensional fractures which developed under EW extension during the East Sea opening in the Early Miocene (before about 17 Ma). The mean-strikes of the basic dikes intruding into the granites are more clockwise rotated in farther eastern side, i. e.$ N06^{\circ}$E, $Nl5^{\circ}$E, and $N37^{\circ}$E in the western side, in the just vicinities, and in the eastern side of the YBonil Tectonic Line (YTL), respectively. And the mean-strike of the basic dikes nearby shoreline is also most clockwise rotated ($N75^{\circ}$E in the Guryongpo Peninsula). The spatial variance indicates that the dikes, located only in the east of the YTL, experienced horizontal-clockwise rotation, and that the dikes in farther east from the YTL experienced more clockwise rotation. It is, thus, supported that the NNW dextral shear stress, generated by the spreading of the East Sea, was propagated toward inland from eastern continental margin of the Korean Peninsula, and that the YTL is an westernmost limit of the clockwise crustal rotations which are pervasively observed in the vicinities of the Miocene basins, SE Korea.

• The Journal of the Petrological Society of Korea
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• v.20 no.4
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• pp.173-189
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• 2011

Basic to acidic dykes and systematic joints are observed pervasively in the Jukbyeon-Bugu area, Uljin, east Korea. In order to classify the dykes and joints and to determine the relative chronology, their geometries, kinematics, and cross-cutting relationships, and the petrography and geochemistry of dykes are synthetically analyzed. Based on the orientations and cross-cutting relationships of 144 dykes (137 basic and 7 acidic dykes) and 370 systematic joints, three basic dike swarms (M-10, M-80, and M-100), one acidic dyke group (AD), and four joint sets (J-10, J-40, J-80, and J-150) are classified. Some of the J-150 joints reactivated as dextral strike-slip fault are recognized in the field and named as F-340R. According to petrographic, geochemical, and occurrence features in the field, M-80 and M-100 dykes have originated from a co-magma and intruded under the same stress field, even though they have intruded through different passages, preexisting fractures and new fractures created by magmatic pressure, respectively. And the relative chronology of dyke swarms and joint sets in the study area is determined as follows : ${\rightarrow}$ ${\rightarrow}$ ${\rightarrow}$ ${\rightarrow}$ ${\rightarrow}$ . And the M-80 (M-100) and M-10 dyke swarms intruded under NNE-SSW and NW-SE trending horizontal minimum stress fields, respectively. According to a synthesis of the results of the previous and this studies, the M-80, M-10, and F-340R are interpreted to have been formed about 64-52 Ma, Eocene~Oligocene, and Miocene, respectively.