Chang Whan Oh

First Finding of Eclogite Facies Metamorphic Event in South Korea and Its Correlation with the Dabie‐Sulu Collision Belt in China

Metabasite lenses occur within granitic gneiss at Bibong in the southwestern part of the Gyeonggi massif, South Korea. Bibong metabasites experienced an initial eclogite facies metamorphism (17.0–20.9 kbar, 835°–860°C), which was succeeded by a granulite facies metamorphism (11.5–14.6 kbar, 830°–850°C) and finally overprinted by an amphibolite facies metamorphism (6.7–11.0 kbar, 570°–740°C). The metabasites have Sm‐Nd internal isochron ages at 225–258 Ma, and the major elements of the metabasites display an island arc affinity. The petrochemical and geochronological data suggest the southwestern part of the Gyeonggi massif as an extension of the Triassic Dabie‐Sulu collision belt in China.

The Late Permian to Triassic Hongseong-Odesan Collision Belt in South Korea, and Its Tectonic Correlation with China and Japan

We propose a new correlation of Middle Triassic (ca. 230 Ma) eclogites from the Hongseong area of the southwest Gyeonggi Massif, South Korea, with the Dabie-Sulu collision belt of China. Late Permian (ca. 257 Ma) mangerites that intrude the Odesan area in the eastern part of the Gyeonggi Massif show geochemical characteristics of collisional tectonic settings, implying that the Hongseong collision belt extends to the Odesan area. In the Higo terrain of southernmost Japan, sapphirine-bearing granulites and related high-temperature metamorphic rocks reveal ca. 245 Ma ultrahigh-temperature (UHT) metamorphic conditions. This metamorphism is well matched with the 245 ± 10 Ma UHT metamorphism estimated for spinel granulite in the Odesan area, suggesting that the Dabie-Sulu collision zone continues through the Hongseong-Odesan belt into the Higo area and that Paleozoic subduction complexes in southwest Japan represent an eastern extension of the Dabie-Sulu collision belt. The Paleozoic subduction complexes in Japan continue further to the Yanji belt, a Carboniferous and Permian subduction complex along the northeastern boundary of the North China block. These data indicate that Phanerozoic subduction along the margin of the North China block and the collision between the North and South China blocks contributed to formation of the Dabie-Sulu-Hongseong-Odesan-Higo-Yanji belt. P-T estimations reveal that there was a decrease in geothermal gradients and an increase of exhumation rates from east to west along the belt during collision. These gradients resulted in preservation of UHT metamorphism in the Odesan area in Korea and the Higo area in Japan, high-pressure (HP) metamorphism in the Hongseong belt, and ultra high-pressure (UHP) metamorphism in the Dabie-Sulu belt.

Neoproterozoic Bimodal Volcanism in the Okcheon Belt, South Korea, and Its Comparison with the Nanhua Rift, South China: Implications for Rifting in Rodinia

A systematic geochemical examination and zircon U‐Pb dating of Neoproterozoic bimodal volcanic rocks from the Chungju area in the northeast segment of the Okcheon Metamorphic Belt (OMB), South Korea, allow a comparison with similar rocks from the Nanhua Rift, South China. The bimodal metavolcanics of the Chungju area comprise the subalkaline to alkaline basalts (hereafter “mafic metavolcanic rocks”) and trachytes (hereafter “felsic metavolcanic rocks”). The mafic metavolcanic rocks are characterized by light rare earth element (LREE)‐enriched and “humped” trace‐element patterns with moderate depletions in Sr and Ti and variable but reasonably low ϵNd(T) values between +0.83 and +2.99. These geochemical features are consistent with the areas origin in an ocean island basalt (OIB) mantle source with minor crustal contamination. The felsic metavolcanic rocks are characterized by LREE‐enriched patterns with a remarkable negative Eu anomaly. They display an overall enriched trace‐element pattern with significant depletions of Sr, P, Eu, and Ti. They have the geochemical characteristics typical of A1‐type granites and ϵNd(T) values between +1.30 and +2.54. The incompatible element versus incompatible element diagrams for both rocks exhibit nearly smooth positive trends. In the Y/Nb versus Yb/Ta diagram, all the felsic rocks plot within the OIB field. Hence, our data imply a genetic linkage between the mafic and the felsic rocks. The felsic rocks were most likely generated from basaltic protoliths through extensive fractional crystallization plus minor crustal contamination/assimilation. Igneous zircon from a felsic metavolcanic rock from the Munjuri Formation in the OMB gives a SHRIMP U‐Pb age of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

SHRIMP zircon age of a Proterozoic rapakivi granite batholith in the Gyeonggi massif (South Korea) and its geological implications

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Sr, Nd and Pb Isotopic Systematics of the Cenozoic Basalts of the Korean Peninsula and Their Implications for the Permo-Triassic Continental Collision Boundary

\end{document} Ma, providing a temporal link to the Neoproterozoic rift‐related volcanism in South China. Rare detrital zircons extracted from a felsic sample from the Gyemyeongsan Formation yield a mixture of ages: ∼1.9 Ga, ∼870 Ma, and ∼250 Ma. The presence of some Triassic metamorphic overgrowths reflects a high‐grade metamorphic event coeval with that recently identified in the Gyeonggi and Yeongnam massifs and linked to an Early Triassic collision event in South Korea. The lithological and geochemical data from the Neoproterozoic metavolcanic rocks in the OMB of South Korea show similarities with the Nanhua Rift in South China, pointing to a North Asian connection associated with the disruption of Rodinia.

A Middle Ordovician Drowning Unconformity on the Northeastern Flank of the Okcheon (Ogcheon) Belt, South Korea

The Okcheon metamorphic belt (OMB) in central South Korea is surrounded by Middle Jurassic granitoid batholiths that intruded South Korea extensively; the granitic bodies form a complex about 200 km long and 150 km wide as part of a Mesozoic granite belt along the East Asian continental margin. Middle Jurassic magmatism was related to ridge subduction that occurred around 200 to 166 Ma, with the main magmatic period between 175 and 166 Ma; main cooling ages range from 168 to 152 Ma. The magmatism was divided into two stages: (1) a deeper, earlier stage, which resulted in emplacement of diorite, granodiorite and granite as shown in the northeast OMB; and (2) a shallower, younger stage, which resulted in emplacement of granite and two-mica granite as shown in the southwest OMB. Most granitoids are peraluminous to metaluminous I-type granitoids that originated in a volcanic arc; an exception is an S-type two-mica granite. Inherited cores of 998 and 262 Ma U-Pb SHRIMP II zircon ages from the two-mica granite indicate that two-mica granite is reworked crustal material formed by earlier magmatism before the Middle Jurassic event. Together with previous studies on the Middle Jurassic granitoids, the present result indicates that subduction of the Farallon-Izanagi ridge beneath Asia caused widespread igneous activity throughout South Korea, especially during Middle Jurassic ridge subduction.

The Origin and Age of the Orbicular Granite Gneiss in Wangjungri, Muju

A large rapakivi granite batholith in the Neo-Archaean/Palaeoproterozoic Odesan complex, northeastern Gyeonggi massif, South Korea, has been dated at 1839 ± 10 Ma using SHRIMP U–Pb analysis of zircons. The age, petrological and geochemical characteristics of this batholith are similar to those of the rapakivi granite batholiths exposed in the Rangnim massif of North Korea and in the Miyun–Chengde complex of North China. The country rocks of these rapakivi granite batholiths are also comparable; all are composed of granitic gneisses and banded iron formation (BIF)-bearing supracrustal rocks metamorphosed to amphibolite- to granulite-facies. This study provides new evidence for the suggestion that the Gyeonggi and Rangnim massifs may share an affinity with the Precambrian basement of the North China craton. The study provides new insight into the possible eastward extension of the Sulu orogenic belt in the Korean peninsula and further provides evidence to correlate the Korea basement to a possible global 2.1–1.8 Ga supercontinent.

Genetic environment of the Yuryang Te-bearing Au deposit: Batholith-type orogenic Au mineralization in Korea

Abstract Two distinct ultramafic bodies occur in Baekdong and Bibong in the Hongseong area within Gyeonggi massif of South Korea. The Hongseong area is now extensively documented as an extension of the Dabie-Sulu collision belt in China. The Baekdong ultramafic body has a NWW elongation direction. This elongation trend is similar to the general trend of the Dabie-Sulu collision belt. The Bibong ultramafic body is elongated in a NNE direction and runs parallel to the direction of the main fault in the study area. The Baekdong ultramafic bodies show porphyroclastic and mylonitic textures while those at Bibong exhibit a mosaic texture. Both were grouped into peridotite and serpentinite based on their modal abundance of serpentine. In the olivine (Fo) vs. spinel [Cr# = Cr/ (Cr+Al)] diagram, both ultramafic rocks fall with in olivine spinel mantle array. The compositions of olivine, orthopyroxene and spinel indicate that the Baekdong ultramafic rock formed in deeper parts of the upper-mantle under passive margin tectonic setting. The SREE content of Baekdong ultramafic rock vary from 0.19 to 5.7, exhibits a flat REE pattern in the chondrite-normalized diagram, and underwent 5% partial melting. Conversely, large variation in SREE (0.5 21.53) was observed for Bibong ultramafic rocks with an enrichment of LREE with a negative slope and underwent 17 24% partial melting. The Baekdong ultramafic rocks experienced three stages of metamorphism after a high pressure residual mantle stage. The first stage of metamorphism occurred under the eclogite-granulite transitional facies (1123 911°C, >16.3 kb) the second under the granulite facies (825 740°C, 16.3 11.8 kb) and the third is the retrogressive metamorphism under amphibolite facies (782 718°C, 8.2 8.7 kb) metamorphism. The Baekdong ultramafic rocks had undergone high-P/T metamorphism during subduction of the South China Block, and experienced a fast isothermal uplift, and finally cooled down isobarically. Evidences for metamorphism were not identified in Bibong ultramafic rocks. Hence, the Baekdong ultramafic rocks with in the Hongseong area may indicate a link on the Korean counterpart of Dabie-Sulu collision belt between North and South China Blocks.