• The Journal of the Petrological Society of Korea
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• v.4 no.2
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• pp.144-152
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• 1995

The Jangsan Quartzite of the Joseon Supergroup and the foliated granite (so-called granitlc gneiss of presumed Precambrian age) of the Yeongnam massif are in direct contact at Cheondong-ri area, 6 km @SE of Danyang. sllthough it has been thought traditionally that the Jangsan Quartzite overlies unconformably the f&ted granite, it is difficult to interpret the contact as an unconformity smce the basal conglomerate in- the lower part of the Jangsan Quartzite does not have any clast of the foliated granite, Rather, recent structural studies of this area indlcate that the contact is a ductile shear zone. However, the sense and age of the shear movement are still problematic. Our mesoscopic and microscopic studies of &tre Cheondong-11 semi-brittle shear zone involving foliated cataclasite and phyllonite, which is a pa& of the Ogdong fault, indlcate a top-to-the northeast shearing, i.e., dextral strike slip. We also performed Pb-Pb dating for the age-unknown foliated granite, since the age of deformed granite ccarr emtrain the maximum age of deformation. The whole rock and feldspar Pb isotape data for the foliated granite and a micaceous xenolith define an isoc chron age of $2.16{\pm}0.15$ Ga ($2{\sigma}$;MSWD=4.4) which is interpreted as the emplacement age of the granite. This early Proterozoic age agrees with those of Precambrian igneous activity In the Yeongnam massif reported previously. The obtaiPrfid gge confirms the traditional idea about the age of the foliated granite and indicates that other methd(s) should be employed to constrain the age of the shear movement.

• The Journal of the Petrological Society of Korea
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• v.27 no.3
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• pp.173-184
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• 2018

Geologic structures related to the latest event in the evolution around Gyeongsang Basin are mainly associated with the Yangsan Fault. In particular, the structures in the northern part of the Yangsan Fault are mainly observed in the region between Bogyeongsa Temple and Danguri. Such structures are also clustered in the vicinity of the Yangsan Fault, exhibiting similar geometric and kinematic patterns. In general, N-S and NE-SW trending fractures and tectonogeomorphic lineament are mainly eastward dipping reverse faults, such that the blocks in the east of the structures moved west or northwest. The reverse faults are segmented by NW trending fractures that accommodate strike-slip movements. The reverse faults and geomorphotectonic lineaments related to the latest event of deformation in the northern part of the Yangsan Fault show a westward convex patterns. We infer that these structures were initially normal faults that formed during a NW-SE extensional environment and were later reactivated during an E-W compressional one. Such a deformation pattern is also well developed around Pohang-Heunghae area based on the tectonogeomorphic analysis, which appears to be closely related to the Pohang Earthquake (15 Nov. 2017), and its development of the surface rupture and highly damaged zones.

• Economic and Environmental Geology
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• v.28 no.5
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• pp.493-501
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• 1995

Carboniferous and Cretaceous rock samples were collected from 3 and 12 sites respectively in the vicinity of the Okcheon Zone. Mean directions of characteristic component magnetizations from Carboniferous rocks along the Honam Shearzone reveal that the Okcheon zone was considerably rotated and deformed during Triassic. The amount of rotations were clockwisely $80.3^{\circ}$ in Mungyeong and $42.4^{\circ}$ in Hwasun areas. Mean directions of characteristic component magnetizations obtained from Cretaceous Yeongdong and Neungju Basin were identical to those from the Gyeongsang Basin in the Yeongnam Block indicating no relative motion between them since Cretaceous. Cretaceous paleopole position from 4 locations, $204.9^{\circ}E$ in longitude and $65.1^{\circ}N $ in latitude.

• The Journal of the Petrological Society of Korea
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• v.21 no.2
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• pp.151-171
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• 2012

The Permo-Triassic Songrim orogeny in the Korean peninsula was a major tectonic event involving complicated continental collisions at the eastern margin of Eurasia. Based on the previous studies on the metamorphic and deformations features of the Songrim orogeny, this paper presents metamorphic and structural characteristics and timing of the Songrim orogeny in the Taebaeksan basin, and discuss about correlation of the tectono-metamorphic evolution of the Taebaeksan basin with the Okcheon basin and the Imjingang belt with a combined analysis of bulk crustal shortening direction, metamorphic P-T and T-t (time) paths. The metapelites in the Pyeongan Supergroup in the northeastern margin of the Taebaeksan basin have experienced lower-temperature/medium-pressure (LT/MP) regional metamorphism followed by high-temperature contact metamorphism due to the Jurassic granite intrusion. The earlier LT/MP regional metamorphism produced two loops of clockwise P-T-d (deformation) paths combined with four deformation events ($D_1-D_4$). The first loop concomitant with $D_1$ and $D_2$ occurred at $400-500^{\circ}C$, 1.5-3.0 kbar, and related with growth of syn-$D_1$ chloritoid and andalusite, post-$D_1$ margarite, Ca-rich syn-$D_2$ or post-$D_2$ plagioclase. The second loop accompanying $D_3$ and $D_4$ occurred at $520-580^{\circ}C$, 2.0-6.0 kbar, and associated with the growth of syn-$D_3$ garnet and staurolite, and syn-$D_4$ and/or post-$D_4$ andalusite porphyroblasts. Furthermore the syn-$D_1$ chloritoid and andalusite porphyroblasts grew during E-W bulk crustal shortening, whereas the syn-$D_3$ garnet and staurolite, and the syn-$D_4$ and/or post-$D_4$ andalusite porphyroblasts have grown under N-S bulk crustal shortening. The similarity in the characteristics and timing of the metamorphism and bulk crustal shortening directions between the Okcheon and Imjingang belts suggest that the peak metamorphic conditions tend to increase toward the western part (Imjingang belt and southwestern part of the Gyeonggi Massif) from the eastern part (Taebaeksan basin). The E-W bulk crustal shortening influenced the eastern part of the Okcheon belt, whereas the N-S bulk crustal shortening resulted in strong deformation in the Imjingang and Okcheon belts. Consequently, the Permo-Triassic Songrim orogeny in the Korean peninsula is probably not only related to collision of the North and South China blocks, but also to the amalgamation of terrane fragments at the eastern Eurasia margin (e.g., collision of the Sino-Korean continent and the Hida-Oki terrane).

• The Journal of the Petrological Society of Korea
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• v.21 no.2
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• pp.193-202
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• 2012

There were three cycles of igneous activities from the late Paleozoic to early Cenozoic; Permian to Triassic, Jurassic, and Cretaceous to Paleogene. After the beginning of each igneous activity cycle, igneous activity became more frequent until its climax. It is noteworthy that A-type magmatisms are reported from near the ends of the all three igneous activity cycles. In addition, adakitic magmatisms occurred at the beginning of both the Permian-Triassic and the Cretaceous-Paleogene cycles. Most of the igneous activities during the late Paleozoic to early Cenozoic period were subduction-related. Therefore, transitions among beginning, proceeding, and closing of the igneous activity cycles would be intimately related with changes in directions of plate movements. In this context, I suggest following hypotheses. The closing of the Permian-Triassic igneous cycle was possibly a consequence of radical adjustment of plate motion occurred due to continental collision between north and south China blocks. Considering that no appreciable tectonic activities were recognized from the east Asian continent at the closing of the Jurassic igneous cycle, it seems that one of the strong events related with Gondwanaland-breakup and subsequent birth of the new oceans, which might cause sudden adjustments of plate motions. The closing of the Cretaceous-Paleogene igneous cycle seems to be caused as a consequence of the collision between India and Asia continents. Meanwhile, adakitic igneous bodies emplaced at the beginnings of the Permian-Triassic and Cretaceous-Paleogene cycles could be products of slab-melting during the early stages of the subduction.

• The Korean Journal of Petroleum Geology
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• v.7 no.1_2 s.8
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• pp.28-34
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• 1999

The Cretaceous Poongam sedimentary Basin in Kangwon-do, Korea consists alluvial deposits of conglomerates, sandstones, mudstones or siltstones, and volcaniclastics. The Poongam Basin was formed as a fault margin sag or a transpressional basin developed along a strike-slip fault zone, and received huge amount of clastic sediments from the adjacent fault-scaip. It formed an aggrading alluvial fan system and a volcaniclast-supplied marginal lake environment, while tectonic activity and volcanism attenuated toward the end of basin formation. Following the Folk's classification, the sandstones of the Poongam Basin are identified as lithic wackes or feldspathic wackes. The areal and sequential variation of the mineral composition in the sandstones is not distinct. The results of K-Ar age dating from the intruding andesites, volcaniclastics and volcanic fragments in sedimentary rocks show a range of 70 Ma to 84 Ma. It suggests that volcarism occurred sequentially within a relatively short period as the pre-, syn-, and post-depositional events. It was the short period in the late Cretaceous that the basin had evolved i.e., the basin formation, the sediment input and fill, and the , intrusion and extrusion of volcanic rocks occurred. The Poongam sedimentary sequence is a typical tectonic-controlled coarse sedimentary facies which is texturally immature.

• Geophysics and Geophysical Exploration
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• v.14 no.2
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• pp.127-132
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• 2011

We acquired and interpreted more than 650 km of high-resolution seismic reflection profiles in the Hupo Basin, offshore east coast of Korea at $37^{\circ}N$ in the East Sea (Japan Sea) to image shallow and basement deformation. The seismic profiles reveal that the main depocenter of the Hupo Basin in the study area is bounded by the large offset Hupo Fault on the east and an antithetic fault on the west; however, the antithetic fault is much smaller both in horizontal extension and in vertical displacement than the Hupo Fault. Sediment infill in the Hupo Basin consists of syn-rift (late Oligocene. early Miocene) and post-rift (middle Miocene.Holocene) units. The Hupo Fault and other faults newly defined in the Hupo Basin strike dominantly north and show a sense of normal displacement. Considering that the East Sea has been subjected to compression since the middle Miocene, we interpret that these normal faults were created during continental rifting in late Oligocene to early Miocene times. We suggest that the current ENE direction of maximum principal compressive stress observed in and around the Korean peninsula associated with the motion of the Amurian Plate induces the faults in the Hupo Basin to have reverse and right-lateral, strike-slip motion, when reactivated. A recent earthquake positioned on the Hupo Fault indicates that in the study area and possibly further in the eastern Korean margin, earthquakes would occur on the faults created during continental rifting in the Tertiary.

• Economic and Environmental Geology
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• v.44 no.5
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• pp.413-431
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• 2011

An Epithemal Au-Ag mineralized zone is developed in the Moisan area of Hwangsan-myeon, Haenam-gun, Jeol-lanam-do, Korea, which is located in the southwestern part of the Ogcheon metamorphic zone. It is hosted in the Hwangsan volcaniclastics of the Haenam Formation of the Late Cretaceous Yucheon Group. This research investigated the characteristics of bedding arrangement, fold, fault, fracture system, quartz vein and the time-relationship of the fracture system to understand the geological structure related to the formation of the mineralized zone. On the basis of this result, the tectonic environment at the time of the mineralization was considered. Beds mainly trend east-northeast and gently dip into north-northwest or south-southeast. Their poles have been rearranged by subhorizontal-upright open fold of (east)-northeast trend as well as dip-slip fault. Fracture system was formed through at least 6~7 different deformation events. D1 event; formation phase of the main fracture set of EW (D1-1) and NS (D1-2) trends with a good extensity, D2 event; that of the extension fracture of NW trend, and conjugate shear fracturing of the EW (dextral) and NS (sinistral) trends, D3 event; that of the extension fracture of NE trend, and conjugate shear refracturing of the EW (sinistral) and NS (dextral) trends, D4 event; that of the extension fracture of NS trend showing a poor extensity, D5 event; that of the extension fracture of NW trend, and conjugate shear refracturing of the EW (dextral) and NS (sinistral) trends, D6 event; that of the extension fracture of EW trend showing a poor extensity. Frequency distribution of fracture sets of each deformation event is D1-1 (19.73 %)> D1-2 (16.44 %)> D3=D5 (14.79 %)> D2 (13.70 %)> D4 (12.33 %)> D6 (8.22 %) in descending order. The average number of fracture sets within 1 meter at each deformation event is D6 (5.00)> D5 = D4 (4.67)> D2 (4.60)> D3 (4.13)> D1-1 (3.33)> D1-2 (2.83) in descending order. The average density of all fractures shows 4.20 fractures/1 m, that is, the average spacing of all fractures is more than 23.8 cm. The frequency distribution of quartz veins at each orientation is as follows: EW (52 %)> NW (28 %)> NS (12 %)> NE (8 %) trends in descending order. The average density of all quartz veins shows 4.14 veins/1 m, that is, the average spacing of all quartz veins is more than 24.2 cm. Microstructural data on the quartz veins indicate that the epithermal Au-Ag mineralization (ca. 77.9~73.1 Ma) in the Moisan area seems to occur mainly along the existing D1 fracture sets of EW and NS trends with a good extensity not under tectonic stress but non-deformational environment directly after epithermal rupture fracturing. The D1 fracturing is considered to occur under the unstable tectonic environment which alternates compression and tension of NS trend due to the oblique northward subduction of the Izanagi plate resulting in the igneous activity and deformation of the Yucheon Group and the Bulguksa igneous rocks during Late Cretaceous time.

• Journal of the Korean Geographical Society
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• v.47 no.3
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• pp.328-346
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• 2012

This study provides quantitative constraints on Neogene uplift in the Korean peninsula using onshore paleo-shoreline records and seismic data. The eastern margin of Northeast Asia including Korea sits in the back-arc system behind the Western Pacific Subduction Zone, a complex trench triple junction of the Philippine Sea, Pacific, and Eurasian (Amurian) plates. An analysis of seismic data in the subduction zone shows that the pattern of uplift in the peninsula mirrors the extent of deep seismicity in subducting Pacific plate beneath. Combined with previous tomographic studies it is proposed that uplift is partly driven by asthenospheric upwelling caused by a sinking slab during the Neogene. In addition, the SHmax orientations of E-W and N-S trends in the peninsula are consistent with the prevailing in-situ stress fields in the eastern Eurasian continent generated by various plate boundary forces. The uplift in Korea during the Late Neogene is attributed, in part, to lithospheric failure relating to faulting movements, thus providing a link between dynamic effects of mantle upwelling at sinking slab edge and lithospheric responses driven by plate boundary forces.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.14 no.2
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• pp.90-101
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• 2009

Analysis of multi-channel seismic reflection data from the Southern Ulleung Basin reveals that Plio-Quaternary section in the area consists of nine stacked sedimentary units separated by erosional unconformities. On the southern slope, these sedimentary units are acoustically characterized by chaotic seismic facies without distinct internal reflections, interpreted as debris-flow bodies. Toward the basin floor, the sedimentary units are defined by well-stratified facies with good continuity and strong amplitude, interpreted as turbidite/hemipelagic sediments. The seismic facies distribution suggests that deposition of Plio-Quaternary section in the area was controlled mainly by tectonic movement and sea-level fluctuations. During the Pliocene, sedimentation was mainly controlled by tectonic movements related to the back-arc closure of the East Sea. The back-arc closure that began in the Miocene caused compressional deformation along the southern margin of the Ulleung Basin, resulting in regional uplift which continued until the Pliocene. Large amounts of sediments, eroded from the uplifted crustal blocks, were supplied to the basin, depositing Unit 1 which consists of debris-flow deposits. During the Quaternary, sea-level fluctuations resulted in stacked sedimentary units (2-9) consisting of debris-flow deposits, formed during sea-level fall and lowstands, and thin hemipelagic/turbidite sediments, deposited during sea-level rise and highstands.