• Economic and Environmental Geology
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• v.31 no.1
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• pp.45-52
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• 1998

Paleomagnetic data have been obtained from the Lower Triassic Tonggo Formation which is exposed in Tanyang area comprising the Pyeongan Supergroup in eastern Korea. Mean characteristic direction of the Tonggo Formation is declination/inclination=$121.4^{\circ}/-26.4^{\circ}$ (k=52.7, ${\alpha}_{95}=7.2^{\circ}$, N=9 Sites) and paleopole at longitude/latitude=$30.7^{\circ}E/33.3^{\circ}N$ ($dp/dm=4.2^{\circ}/7.8^{\circ}$). The mean direction passes reversal test and fold test at 99% confidence level. Therefore, it is inferred to be a pre-folding component. The paleopole position of this study is close to the Triassic pole positions of the North China Block; it is far from those of the South China Block. Therefore, a first order correlation between the Korean Peninsula and North China at least since Lower Triassic times is identified in this study.

• The Journal of the Petrological Society of Korea
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• v.16 no.3
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• pp.180-188
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• 2007

We carried on CHIME zircon age dating for the Gamaksan alkaline meta-granitoid (GAM) from the northwestern margin of the Gyeonggi massif, and obtained a timing of regional metamorphism at $247{\pm}14Ma$ (n=103, MSWD=0.92). The age is compatible with Permo-Triassic regional metamorphic ages from the Imjingang Belt which has been regarded as possible eastward extension of Triassic collisional belt in China. Considering an extensional ductile shearing of the Gyeonggi (Kyonggi) Shear Zone which deformed GAM occurred at 226 Ma with temperature condition about $500^{\circ}C$ (Kim et al., 2000), and the Late Triassic to Early Jurassic Daedong Group unconformably overlies on top of the ductile shear zone, cooling rate of GAM over the period can be estimated as $18{\sim}10^{\circ}C/Ma$. Since new zircon begin to pow at temperature higher than upper-amphibolite facies condition (${\sim}700^{\circ}C$), cooling rate of GAM from peak metamorphism (247 Ma) to deposition of the Daedong G.oup (${\sim}$Early Jurassic) would be higher than $10^{\circ}C/Ma$. Such rapid cooling rate is compatible with that reported from exhumation stage of the Dabie-Sulu Belt, and supports an idea that the Gyeonngi massif is a part of Permo-Triassic orogenic belt in East Asia.

• The Journal of the Petrological Society of Korea
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• v.14 no.4 s.42
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• pp.226-236
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• 2005

Using the concept of granite suite/supersuite we hierarchically divided the Triassic granites in South Korea which have spatio-temporally close relationships each other. Among the Triassic granites in the Okcheon belt (western Yeongnam massif), the Baegrok granite and the Jeomchon granite can be grouped into one suite, the Baegrok suite, whereas the Cheongsan granite into the Cheongsan suite. These two suites can be grouped again into a larger supersuite, the Baegrok supersuite, on the basis of the similarity in the source rocks and the contrasts in the petrographic and geochemical characteristics. Three Triassic granites in the Gyeongsang basin - the Yeongdeok granite, the Yeonghae granite, and the Cheongsong granite - can be grouped into the Yeongdeok suite, Yeonghae suite and Cheongsong suite, respectively. These three suites can be grouped again into a larger supersuite, the Yeongdeok supersuite, on the basis of the similarity in the source rocks and the contrasts in the petrographic and geochemical characteristics. Nd-Sr isotopic signatures for the Baegrok supersuite are quite distinct from those for the Yeongdeok supersuite, indicating that the source materials of each granitic magma were not identical. The source rocks for the Baegrok supersuite are thought to be a mixture of two crustal components of the Yeongnam massif, whereas those for the Yeongdeok supersuite to be a mixture of the depleted mantle with the crustal components of the Yeongnam massif. The fact that the two contemporaneous granite supersuites were derived from the different sources can be explained by the difference of the tectonic environments where the granitic magmas were produced.

• Proceedings of the KSEEG Conference
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• 2003.04a
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• pp.254-257
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• 2003

한반도에 대한 고지자기 연구는 유라시아 대륙의 지구조운동이 진행되었던 중생대 및 고생대암석에 대해 여러 사람들에 의해 활발히 수행되어왔다. 특히 1980년대 후반부터는 북중국지괴와 남중국지괴 사이의 충돌대인 친링-다비-수루 (Qinling-Dabie-Sulu) 조산대가 서해를 지나 한반도로 연장될 가능성에 대한 관심이 높아지고 있다. 한반도의 중부를 가로지르는 옥천대는 경기육괴와 영남육괴의 경제부로서 변성시기가 초기 Triassic으로 보고되고 있으며, 경기육괴 북부 휴전선 인접지역의 동서방향의 주향을 갖는 습곡-단층대인 임진강대는 남북 경계에 대한 정확한 정의는 성립되어있지는 않지만 Triassic에 광역변성작용을 받았다는 보고가 있으나, 이들 임진강대와 옥천대의 성인에 대한 논란은 현재에 이르기까지 계속되고 있다. (중략)

• The Journal of the Petrological Society of Korea
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• v.21 no.2
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• pp.113-128
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• 2012

The chemical composition of the continental crust play an important role in understanding of crustal formation and evolution and quantifying other processes taking place within continental crust. We summarized geochemical data reported in the previous literature for the crustal rocks in the Korean Peninsula and divided their chemical composition into geologic time scale. In the variation diagram normalized by average composition of the upper crustal rocks, the geochemical characteristics of the upper crust during Triassic period is different from those of the upper crustal rocks after Jurassic period or before Precambrian. However, the geochemical characteristics of the Jurassic and Precambrian period are similar each other. Our summarized data indicate that the source material of Triassic upper crust may be different from that of Jurassic or Precambrian upper crust.

• Economic and Environmental Geology
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• v.26 no.2
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• pp.193-206
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• 1993

A total of 111 independently oriented core samples were drilled at 12 sites in fue Kimpo area ($37.70^{\circ}N$, $126.55^{\circ}E$) of the Taedong Supergroup. The Taedong strata are composed of sandstone, conglomeratic sandstone, shale and thin coal seams. The age of the strata is known to be Late Triassic-Early Jurassic according to freshwater Esfuerites and plant fossil (Dictyophyllum-Clathropteris flora) contents. Through AF and thermal demagnetization, an area-mean ChRM direction of $D=48.3^{\circ}\;I=40.3^{\circ}\;{\alpha}_{95}=7.9^{\circ}\;k=59.5$, n=7 was obtained. It passed fold and reversal test in the formation-mean level. Fold test was not significant in the area-mean level. The palaeomagnetic north pole calculated from the area-mean lies at $46.3^{\circ}N$, $222.0^{\circ}E$ with dp=5.7, $dm=9.5^{\circ}$. This pole position is very similar to those of the South China Block (SCB) in Triassic times. Palaeolatitude of the Kimpo area in the Taedong times was $23.0^{\circ}N$, again very similar to the palaeolatitude of the South China Block in the Late Triassic. This low latitude of the study area at the time of deposition explains the tropical-subtropical nature of fossil contents of the Taedong Supergroup.

• The Journal of the Petrological Society of Korea
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• v.18 no.3
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• pp.255-267
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• 2009

The intrusive rocks in the Hudongri area, Chuncheon located in central Gyeonggi Massif consist of gabbroic diorite and diorite. K-Ar age of biotite separated from diorite sample records middle Triassic age of 228 Ma. The intrusives are characterized by enrichment of MgO, Ni and Cr as well as large ion lithophile elements such as Sa and Sr, which is indicative of derivation of magma from enriched mantle. The intrusives also have enriched Sr-Nd isotopic compositions, which appear to result from a long-term incompatible element enriched mantle source with an effect of crustal contamination. Occurrence of abundant hydrous minerals such as amphiboles and biotite rather than anhydrous minerals of pyroxene and olivine in mafic intrusive as well as being plotted in volcanic arc field in tectonic environment discrimination diagram indicate the mafic-intermediate intrusives in the Hudongri area, Chuncheon were derived from mantle material enriched by subduction.

• The Journal of the Petrological Society of Korea
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• v.23 no.4
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• pp.293-309
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• 2014

The Qinling-Dabie-Sulu-Hongseong-Odesan collision belt was formed by the collision between the North China and South China Cratons during late Permian to Triassic. During the collision, Triassic post-collision igneous rocks regionally intruded in the Qinling and the Hongseong-Odesan collision belts which represent the western and eastern ends of the collision belt, respectively. However, no and minor Triassic post-collision igneous activities occur in the Dabie and Sulu belts respectively. The peak metamorphic pressure conditions along the Qinling-Dabie-Sulu-Hongseong-Odesan belt indicate that the slab break-off occurred at the depth of ultra-high pressure (UHP) metamorphic condition in the Dabie and Sulu belts and at the depths of high pressure (HP) or high pressure granulite (HPG) metamorphic condition in the Qinling and Hongseong-Odesan belts. In the Dabie and Sulu belts the heat supply from the asthenospheric mantle through the gab formed by slab break-off could not cause an extensive melting in the lower continental crust and lithospheric mantle directly below it due to the very deep depth of slab break-off. On the other hand, in the Qinling and Hongseong-Odesan belts, shallower slab break-off caused the emplacement of regional post collision igneous rocks. The post-collision igneous rocks occur in the area to the north of the Mianlu Suture zone in the western Qinling belt and crop out continuously eastwards into the areas to the north of the Shangdan Suture zone in the eastern Qinling belt through the areas within the South Qinling block. This distribution pattern of post collision igneous rocks suggests that the Triassic collision belt in the Mianleu Suture zone may be extended into the Shangdan Suture zone after passing through the South Qinling block instead into the boundary between the South Qinling block and the South China Craton.

• Economic and Environmental Geology
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• v.30 no.6
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• pp.613-624
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• 1997

A study of anisotropy of magnetic susceptibility (AMS) was conducted on the Ordovician-Eocene strata in the Taebaek area. The study area is a northeastern part of the Okchon belt, sometimes called as Paegunsan Synclinal Area. A total of 600 independently oriented samples were collected from 60 sites covering the whole area. With a few exception of late Cretaceous-Eocene volcanic rocks, all the sampled strata are nonmetamorphosed sedimentary rocks, mainly sandstones. Among the 60 sites, 5 sites showed flow lineation lying on the bedding plane, 11 sites showed load foliation parallel to the bedding plane, and 21 sites showed tectonic foliation unrelated to the bedding plane. The tectonic foliations are defined by $k_1-k_2$ ($k_{max}-k_{int}$) anisotropy plane, and are considered as a result of tectonic forces acted perpendicularly to the foliation plane in the geologic past. Regardless of sample-site locations, tectonic force directions defined by $k_3$ ($k_{min}$) axis perpendicular to the tectonic foliation are consistent among the strata of the same geologic age. In the course of geologic time, however, the tectonic force directions showed a clockwise rotation: approximately E-W in the Ordovician sites, NW-SE in the Permian sites, N-S in the Triassic sites, and lastly NE-SW in the late Cretaceous-Eocene sites. The pre-Permian directions showed better clustering in the in-situ (geographic) coordinates, while the younger directions become better clustered after the bedding-tilt correction. It is interpreted that the major tectonic structures of the Taebaek area were controlled by the above-mentioned tectonic forces: The Paegunsan Syncline and the Hambaeksan Fault must have been generated by the NW-SE force of late Permian-early Triassic time. It was then reactivated in the reverse (dextral) sense by the N-S force of Triassic time. The Osipchon Fault in the eastern part of the study area was either generated or reactivated by the NE-SW force of late Cretaceous-Eocene time. The Permo-Triassic NW-SE force should be an expression of the Songnim Disturbance in the Korean peninsula, which is in turn related with the SCB/NCB collision in China.

• 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.