• Economic and Environmental Geology
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• v.41 no.2
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• pp.173-181
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• 2008

CHIME ages were obtained from monazites in metamorphic rocks from the Seosan and Siheung Groups in the Gyeonggi gneiss complex, Korean peninsula. Monazite CHIME ages range from 234 to 257 Ma, corresponding to the late Permian to middle Triassic Songrim disturbance due to the collision event between the North and South China blocks within the Gyeonggi gneiss complex in the Korean peninsula. The CHIME ages are consistent with the metamorphic ages from the Hongseong area (231 Ma, Kim et al., 2006) and the Odesan area (245-248 Ma, Oh et al., 2006b) in the Gyeonggi gneiss complex and are older than those from the Dabie-Sulu collision belt (220${\sim}$242 Ma, Yang or of., 2003; Liu et al., 2003, 2004) suggesting that the collision between the North and South China blocks had occurred earlier in Korea than China.

• The Journal of the Petrological Society of Korea
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• v.16 no.3
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• pp.101-115
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• 2007

The CHIME (chemical Th-U-total Pb isochron method) dating on monazite was carried out for two foliated granites from a dextral ductile shear zone in the vicinity of Gangjin area, which is considered to be a southern extension of Sunchang shear zone. The result gives emplacement age of the medium-grained biotite granite and the coarse-grained biotite granite as $183.6{\pm}2.2Ma$(MSWD=0.21) and $171.7{\pm}4.0Ma$(MSWD=0.57), respectively. Microtextures of quartz and feldspar observed in the foliated granite are almost identical with those reported in Jurassic (ca 180 Ma) foliated granites from the Imsil-Namwon area of the Sunchang shear zone, and they constraint that the ductile deformation took place at temperature condition of $300{\sim}550^{\circ}C$. Assuming cooling curves of the foliated granites in this study are similar with those of Jurassic foliated granites from Imsil-Namwon area, dextral ductile shear in the Gangjin area would take place between 172 Ma and 150 Ma, about 10 Ma later than the previous estimation based on CHIME monazite ages.

• The Journal of the Petrological Society of Korea
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• v.16 no.1 s.47
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• pp.1-11
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• 2007

CHIME (chemical Th-U-total Pb isochron) geochronology were made for Precambrian rocks from Goseong-Ganseong area, northeastern part of the Gyeonggi massif. Zircon and/or monazite grains from orthogneisses give $1672{\pm}69\;to\;1414{\pm}36Ma$ ages, and monazite grains from paragneisses yield similar ages ranging from $1703{\pm}70\;to\;1395{\pm}97Ma$ suggesting that $1.7{\sim}1.4Ga$ igneous intrusions and coeval metamorphisms were occurred over the area. Together with reported prevailing $1.9{\sim}1.8Ga$ igneous activities and regional metamorphism from the Cyeonggi massif, our age data from Goseong-Ganseong area would be potentially correlated with long-lived $(1.8{\sim}1.3Ga)$ global tectonotermal events in marginal outgrowth of supercontinent Columbia which was finally assembled by collisional orogenies at ${\sim}1.8Ga$. Petrological and geochmical studies, however, should be followed to confirm this tectonic interpretation.

• 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.17 no.2
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• pp.51-56
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• 2008

The geologic age of the Okcheon metamorphic belt, used to be a longstanding puzzle, has been settled down to Neoproterozoic to Paleozoic with discovery of fossils and isotopic age dating of metavolcanic rocks. As isotopic ages become accumulated, there appeared a controversy over the age of peak metamorphism in the Okcheon metamorphic belt, i.e., a single late Permian-early Triassic metamorphism (CHIME allanite age and U-Pb age of metamorphic zircon), or earlier independent presence of early Permian metamorphism (U-Pb age of allanite within garnet porphyroblast). If we compare the isotopic ages that can represent metamorphism, the data for the latter have much larger error than those of the former with some overlap considering the error limits. It means that, the former, supported by two independent ages, is considered a better representation for the age of metamorphism of the Okcheon metamorphic belt. Therefore, I propose the idea of early Permian metamorphism should better be reserved until conclusive evidence appears. The late Permian-early Triassic metamorphic age suggest that the effect of continental collision influenced much of the middle part of Korean Peninsula, namely, the Imjingang belt, the Gyeonggi massif and the Okcheon belt.

• Proceedings of the KSEEG Conference
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• 2001.04a
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• pp.218-218
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• 2001