• The Journal of the Petrological Society of Korea
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• v.6 no.2
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• pp.77-85
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• 1997

The Early Proterozoic reworked rock association occurs within the Preacmbrian high grade metamorphic rocks in the area of Daqingshan, Inner Molgolia. In this association, the various large scale ductile deformation belts, form a nappe structure where the foliation steeply dips to north and the lineation ($340^{circ}-30^{\circ}$) plunges at $45^{\circ}55^{\circ}$. This result indicates the subduction/extension with northern part thrusting over the southern part at high angle. The southern subducted microlithon has the characteristics of prograde metamorphism. The northern thrusted microlithon shows the evidence of retrograde metamorphism with decreasing pressure and increasing temperature. The main rock types of Early Proterozoic Moyites are biotite adamellite and syenogranites occurring in the form of small batholiths or stocks and alkali-feldspar granites in veins. The biotite adamellites are progressively contacted with the Archean and Early Proterozoic rocks and contain a great deal of enclaves of metamorphosed rocks, suggesting an anatexis origin. The geochemical characteristics of moyites show the typical features of anatexis granite. At middle to late Early Proterozoic time, the continent-continent collision formed the large scale thrusting and imbrication of Archean basement rocks. According to the mineral assemblage and thermobarometer of Paria et al. (1988) give the following P-T condition : up-faulted block; $700-710^{\circ}C$, 0.72-0.78 Gpa (early stage) and $600^{\circ}C$, 0.44 Gpa (late stage), footwall block; $620^{\circ}C$, 0.8 Gpa (early stage), $620-840^{\circ}C$, 0.64-0.45 Gpa (peak) and $620-630^{\circ}C$, 0.35Gpa (late stage). These results suggest a clockwise P-T-t path (jin et al., 1991, 1994). According to the depth-temperature model in the comperature subduction zone and the experimental data of Wyllie et al. (1983), we propose a tectonic-magmatic-thermal model to account for metamorphism-anatexis of moyite occurring in subduction-shear zone.

• The Journal of the Petrological Society of Korea
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• v.27 no.3
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• pp.121-138
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• 2018

We have examined the petrotectonic setting and magmatic evolution from petrochemical characteristics of major and trace elements for the Cretaceous volcanic rocks in and around the Mireukdo Island. The volcanic rocks, can be devided into Jusasan, Unmunsa, Yokji and Saryang subgroups on the ascending order, are classified as basalt, basaltic andesite, andesite, dacite and rhyolite on TAS diagram. Petrochemical data show that the rocks are calc-alkaline series, and suggest that erupted earlier medium-K series and later high-K series. The volcanic rocks provide a case in which the calc-alkaline magma are formed, not only from separate protoliths, but following separate paths from source to surface. Earlier and later subgroups take different paths to the surface respectively, and are emplaced in the shallow crust as a series of discrete magma chambers through the volcanic processes. After emplacement, each chamber evolves indepently through fractional crystallization with a little assimilation of wall rock. The volcanic rocks have close petrotectonic affinities with orogenic suite and subduction-related volcanic arc. The rhyolitic magma can be derived from calc-alkaline andesitic magma by fractional crystallization with crustal assimilation, which may be derived from a partial melt of peridotite in the upper mantle.

• Economic and Environmental Geology
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• v.51 no.5
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• pp.439-453
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• 2018

The Eocene Gyeongju granitoids in SE Korea are alkali feldspar granite (AGR), biotite granite (BTGR), and hornblende biotite granodiorite (HBGD) along Yangsan fault and Ulsan fault. According to their geochemical characteristics, these granitoids are classified as A-type (AGR) and I-type (BTGR and HBGD) granitoids, and regarded that were derived from same parental magma in upper mantle. The hornblende and biotite of AGR as an interstitial phase indicate that influx of F-rich fluid during the crystallization of AGR magma. AGR is enriched LILE (except Sr and Ba) and LREE that indicate the influences for subduction released fluids. The highest HFSE contents and zircon saturation temperature of AGR among the Eocene Gyeongju granitoids may indicate that it was affected by partial melting rather than magma fractionation. These characteristics may represent that the high F contents of AGR was affected by F-rich fluid derived from the subducted slab and partial melting. It corresponds with the results of the REE modeling and the dehydrated fluid component (Ba/Th) modeling showing that AGR (A-type) was formed by the partial melting of BTGR (I-type) with the continual influx of F-rich fluid derived from the subducted slab.

• Geophysics and Geophysical Exploration
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• v.13 no.3
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• pp.235-242
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• 2010

Two moderate earthquakes with local magnitude 4.9 and 5.0 at the Yellow Sea area occurred successively around Hong island on March 22, 2003 and Baengnyeong island on March 30, 2003, respectively, close to the Korean Peninsula. Focal mechanisms by the waveform inversion analysis are strike slip faulting with a thrust component for the March 22 event, and normal faulting for the March 30 event. The direction of P-axes of two events were ENE-WSW which were similar to previous studies on that of P-axes in and around the Korean Peninsula. Moment magnitudes determined by the waveform inversion analysis were 4.7 and 4.5, respectively, whereas those determined by spectral analysis were 4.8 and 4.6, respectively. As regards the March 22 event, regional stress by combined tectonic forces from compressions of plates colliding to the Eurasian plate, rather than mere local stress, was indicated. However, it was estimated that the March 30 event took place when the weak zone generated from the existing collision zone was reactivated when subjected to local stress in the tensile direction. This seismological observation indirectly supports the idea that the collision zone may extend to the Korean Peninsula.

• Journal of the Korean Geographical Society
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• v.49 no.2
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• pp.200-220
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• 2014

This study reexamines the old concept and reviews prevalent statements on Cenozoic vertical motions of the peninsula that have been uncritically repeated in our academia. The contents of this paper are redefinition of the notion, tilted flexure or warping, and a suggestion for a new time set and properties of the deformation, followed by a new model on its influencing factors and processes. In conclusion, the Cenozoic vertical motion of the Korean peninsula can be reified further with an epeirogenic movement of uplift in the east side-subsidence in the west side of the peninsula since the Neogene (23 Ma). However, the regional boundary for areas of uplift and subsidence is not likely in the Korean peninsula but broader farther to East China and the southern part of Russia. It can be best understood that mantle convection produced by subducting activities in the Western Pacific Subduction Zone causes the uplift and subsidence of earth surface around NE Asia. In addition, faultings in the upper lithosphere induced by in-situ plate boundary stresses accelerate regional uplift in the peninsula since the Quaternary. Controversies that are still standing such as current uplift movements along the western coast of the peninsula during the late Quaternary could be precisely discussed with future research providing detailed information on it.

• Journal of the Korean earth science society
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• v.37 no.1
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• pp.62-77
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• 2016

In the early model of plate tectonics, the plate was depicted as a passive raft floating on the convecting mantle and carried away by the mantle flow. At the same time, ridge push at spreading boundaries and drag force exerted by the mantle on the base of lithosphere were described as the dominant driving forces of plate movements. However, in recent studies of plate tectonics, it is generally accepted that the primary force driving plate motion is slab pull beneath subduction zones rather than other forces driven by mantle convection. The current view asserts that the density contrast between dense oceanic lithosphere and underlying asthenosphere is the substance of slab pull. The greater density of oceanic slab allows it to sink deeper into mantle at trenches by gravitational pull, which provides a dominant driving force for plate motion. Based on this plate tectonics development, this study investigated the contents of plate tectonics in high school Earth Science textbooks and how they have been depicted for the last few decades. Results showed that the early explanation of plate movement driven by mantle convection has been consistently highlighted in almost all high school textbooks since the 5th curriculum, whereas most introductory college textbooks rectified the early theory of plate movement and introduced a newly accepted theory in revised edition. Therefore, we suggest that the latest theory of plate tectonics be included in high school textbooks so that students get updated with recent understanding of it in a timely manner.

• The Journal of the Petrological Society of Korea
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• v.20 no.4
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• pp.191-206
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• 2011

The emplacement ages, whole-rock geochemistry and Sr-Nd isotopic compositions of granitoid rocks from Cheongju area, South Korea, were investigated for delineating their petrogenetic link to the Jurassic Daebo granitoid rocks. Zircon crystals were collected from the diorite, biotite granite and acidic dyke samples in a single outcrop. Cross-cutting relationships show that the emplacement of diorite was postdated by the intrusion of biotite granite. Both rocks have been subsequently intruded by acidic dyke. The U-Pb isotopic compositions of zircon from the diorite, biotite granite, and acidic dyke were measured using a SHRIMP-II ion microprobe, yielding the crystallization ages of $174{\pm}2Ma$, $170{\pm}2Ma$, and $170{\pm}5Ma$, respectively, with 95% confidence limits ($t{\sigma}$). The emplacement ages are consistent with those determined from the above relative ages. The major and trace element patterns of the rocks are consistent with those of the Jurassic Daebo granitoid rocks, possibly suggesting a subduction-related I-type granite. The geochemical signature is, however, betrayed by the Sr and Nd isotopic compositions of these rocks. The isotopic signatures suggest that the rocks were produced either by the partial melting of lower-crust or by the mantle-derived magma contaminated by the basement rocks during its ascent and/or emplacement. In addition, the inherited ages of zircons of the rocks (ca. 2.1, 1.8, 0.8 and 0.4 Ga) suggest a possible assimilation with crustal rocks from the Gyeonggi massif and Ogcheon metamorphic belt.

• Journal of Science Education
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• v.32 no.2
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• pp.121-145
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• 2008

The purposes of this study were to identify the misconceptions that students have on the magma and plate tectonics and to present the implications in developing textbooks as well as related curriculum of high school textbooks. Data were collected through questionnaire, consisting of some questions, short essays, and descriptive drawings, developed by the research team. A total of 140 high school students(9th graders) responded to those questionnaires and were interviewed for further information. It was reported that participants displayed various misconceptions related to magma and plate tectonics. The identified misconceptions are as follows: For the definition of magma, the 31% of participants misunderstood magma as lava. In respect to the generative mechanism of magma at subduction zone, over 90% of students responded that it is generated by frictional heat. The source of misconceptions were identified as a result from textbooks and related reference-books. For the concept of plates, 87% of students conceived 'crust or a lower part of the plates' as 'plates'. Most participants hold the right concept of oceanic ridge, whereas, 66% of them considered 'rift valley' as either 'divergence of continental plates' or 'converging boundary'. 63% of them defined 'collision boundary of continental plate' as either 'subduction zone' or 'diverging boundary'. For the definitions of the trench and Benioff zone, 86% of students responded them as the place of subduction or differing density between two converging plates. The students' misconceptions were resulted from the errors and insufficient explanation, inappropriate figures, and data presented in textbooks, reference-books, lecture, and web sites. The results of this study are implied to contribute the improvement of students' misconceptions.

• The Journal of the Petrological Society of Korea
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• v.19 no.1
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• pp.67-87
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• 2010

This article deal with petrotectonic setting and petrogenesis from petrography and chemical analyses of the Cretaceous volcanic and intrusive rocks in the Cheolwon basin. The volcanic rocks are composed of basalts in Gungpyeong Formation, Geumhaksan Andesite, and rhyolitic rocks (Dongmakgol Tuff, Rhyolite and Jijangbong Tuff), and intrusive rocks, Bojangsan Andesite, granite porphyry and dikes. According to petrochemistry, these rocks represent medium-K to high-K basalt, andesite and rhyolite series that belong to calc-alkaline series, and generally show linear compositional variations of major and trace elements with increase in $SiO_2$ contents, on many Harker diagrams. The incompatible and rare earth elements are characterized by high enrichments than MORB, and gradually high LREE/HREE fractionation and sharp Eu negative anomaly with late strata, on spider diagram and REE pattern. Some trace elements exhibit a continental arc of various volcanic arcs or orogenic suites among destructive plate margins on tectonic discriminant diagrams. These petrochemical data suggest that the basalts may have originated from basaltic calc-alkaline magma of continental arc that produced from a partial melt of upper mantle by supplying some aqueous fluids from a oceanic crust slab under the subduction environment. The andesites and rhyolites may have been evolved from the basaltic magma with fractional crystallization with contamination of some crustal materials. Each volcanic rock may have been respectively erupted from the chamber that differentiated magmas rose sequentially into shallower levels equivalenced at their densities.

• The Journal of the Petrological Society of Korea
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• v.21 no.2
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• pp.59-87
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• 2012

Recent studies reveal that eclogite formed in the Hongseong area and post collision igneous rocks occurred throughout the Gyeonggi Massif during the Triassic Songrim Orogeny. These new findings derive the tectonic model in which the Triassic Qinling-Dabie-Sulu collision belt between the North and South China blocks extends into the Hongseong-Yangpyeong-Odesan collision belt in Korea. The belt may be further extended into the late Paleozoic subduction complex in the Yanji belt in North Korea through the Paleozoic subduction complex in the inner part of SW Japan. The collision belt divides the Gyeonggi Massif into two parts; the northern and southern parts can be correlated to the North and South China blocks, respectively. The collision had started from Korea at ca. 250 Ma and propagated to China. The collision completed during late Triassic. The metamorphic conditions systematically change along the collision belt:. ultrahigh temperature metamorphism occurred in the Odesan area at 245-230Ma, high-pressure metamorphism in the Hongseong area at 230 Ma and ultra high-pressure metamorphism in the Dabie and Sulu belts. This systematic change may be due to the increase in the depth of slab break-off towards west, which might be related to the increase of the amounts of subducted ocecnic slab towards west. The wide distribution of Permo-Triassic arc-related granitoids in the Yeongnam Massif and in the southern part of the South China block indicate the Permo-Triassic subduction along the southern boundary of the South China block which may be caused by the Permo-Triassic collision between the North and South China blocks. These studies suggest that the Songrim orogeny constructed the Korean Peninsula by continent collision and caused the subduction along the southern margin of the Yeongnam Massif. Both the northern and southern Gyeonggi Massifs had undergone 1870-1840 Ma igneous and metamorphic activities due to continent collision and subduction related to the amalgamation of Colombia Supercontinent. The Okcheon metamorphic belt can be correlated to the Nanhua rift formed at 760 Ma within the South China blocks. In that case, the southern Gyeonggi Massif and Yeongnam Massif can be correlated to the Yangtz and Cathaysia blocks in the South China block, respectively. Recently possible Devonian or late Paleozoic sediments are recognized within the Gyeonggi Massif by finding of Silurian and Devonian detrital zircons. Together with the Devonian metamorphism in the Hongseong and Kwangcheon areas, the possible middle Paleozoic sediments indicate an active tectonic activity within the Gyeonggi Massif during middle Paleozoic before the Permo-Triassic collision.