• Economic and Environmental Geology
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• v.46 no.5
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• pp.391-409
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• 2013

The Hongseong area of the southwestern Gyeonggi massif is considered to be part of suture zone that is tectonically correlated with the Qinling-Dabie-Sulu belt of China in terms of the preservation of collisional evidences during Triassic in age. The Wolhyeonri complex, preserved at the center of the Hongseong area, consists mainly of Neoproterozoic orthogneisses and Middle Paleozoic intermediate- to high-grade metamorphic schists, orthogneisses and mafic metavolcanics. The area includes various Middle to Late Triassic intrusives (e.g. dyke or stock). They are mainly monzonite and aplite with small intrusions of monzodiorit, syenite and diorite in composition. The SHRIMP U-Pb zircon ages yield 237 Ma to 222 Ma. The geochemistry of the studied Triassic intrusives show similar subuction- or arc-type signatures having Ta-Nb troughs, depletion of P and Ti, and enrichment of LILEs (large ion lithophile elements). In addition, the Triassic plutons in the Hongseong area, including those from this study, mostly possess high-K calc-alkaline to shoshonitic tectonic affinity. These results could be tectonically correlated to the post-collisional magmatic event following the Triassic collision between the North and South China blocks in China. Therefore, the Triassic plutons in the Hongseong area offer an important insight into the Triassic geodynamic history of the NE Asian region.

• The Journal of the Petrological Society of Korea
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• v.2 no.2
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• pp.104-121
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• 1993

Fission track (FT) thermochronological analyses on Mesozoic granites provide new information about cooling and uplift histories in Southeast Korea. Twenty-nine new FT sphene, zircon and apatite ages and seven track length measurements are presented for eleven granite samples. Measured mineral ages against assumed closure temperatures yield cooling rates for each sample. Relatively rapid (7-$15^{\circ}C$/Ma) and simple cooling patterns from the middle Cretaceouss (ca. 90-100 Ma) granites are caused mainly by a high thermal contrast between the intruding magma and country rocks at shallow crustal levels (ca. 1-2.5 km-depths). On the contrary, a slow overall cooling (1-$4^{\circ}C$/Ma) of the Triassic to Jurassic granites (ca. 250-200 Ma), emplaced at deep depths (>>9 km), may mainly depend upon very slow denudation of the overlying crust. The uplift history of the Triassic Yeongdeog Pluton in the Yeongyang Subbasin, west of the Yangsan Fault, is characterized by a relatively rapid uplift (~0.4 mm/a) before the total unroofing of the pluton in the earliest Cretaceous (~140 Ma) followed by a subsidence (~0.2mm/a) during the Hayang Group sedimentation. Stability of original FT zircon ages (156 Ma) and complete erasure of apatite ages suggest a range of 3 to 5.5 km for the basin subsidence. Since 120 Ma up to present, the Yeongyang Subbasin has been slowly uplifted (~0.04 mm/a). The FT age patterns of Jurassic granites both from the northeastern wing of the Ryeongnam Massif and from the northern edge of the Pohang-Kampo Block indicate that the two geologic units have been slowly uplifted with a same mean rate (~0.04 mm/a) since early Cretaceous. Estimates of Cenozoic total uplifts since 100 Ma are different: Ryeongnam Massif (~6 km)=Pohang-Kampo Block (~6 km)>Yeongyang Subbasin(~4 km).

• The Journal of the Petrological Society of Korea
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• v.2 no.2
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• pp.122-129
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• 1993

We report Rb-Sr whole rock, K-Ar and fission track mineral ages for the Chuncheon granite in the Precambrian Gyeonggi massif. The Rb-Sr whole rock define an age of $196{\pm}9$ Ma with an initial ratio of $0.7159{\pm}0.0006$, suggesting that the granitic magma might have been generated from crustal sources (S-type), or probably mixed mantle and crustal materials, and emplaced into the massif in the late Triassic or the early Jurassic. K-Ar mineral ages of hornblende, muscovite and biotite are ~210 Ma, ~180 Ma and 166-170 Ma respectively, and fission track zircon and apatite ages are 65-70 Ma, ~35 Ma respectively. These ages indicate that the granitic magma might have been emplaced at about 7 to 9 km from the paleosurface, and rapidly cooled down up to $300^{\circ}C$ until middle Jurassic (~170 Ma) with a rate of about $10^{\circ}C$/Ma, due to thermal difference between the magma and the wall rock. During middle Jurassic to late Cretaceous (about 170-70 Ma), the granite pluton is assumed to have uplifted to 4 to 6 km level under the paleosurface with a rate of 30 m/Ma and slowly cooled down with a rate of about $1^{\circ}C$/Ma owing to relatively slow denudation of the massif. In late Cretaceous to the present, the pluton might have more rapidly uplifted to the present level with a rate of 85 m/Ma and rapidly cooled down with a rate of about $3^{\circ}C$/Ma compared to those of middle Jurassic to late Cretaceous time because of extensive igneous activities accompanied by tectonism in the Gyeonggi massif.