• Journal of the Korean earth science society
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• v.43 no.5
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• pp.618-638
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• 2022

The Middle Jurassic granite dike swarm intruding into the Paleoproterozoic banded gneiss is pervasively observed in Ueumdo, Hwaseong City, mid-western Gyeonggi Massif. Based on their cross-cutting relationships in a representative outcrop, there are four dikes (UE-A, UE-C, UE-D, UE-E), and depending on the direction, there are three granite dike groups, which are NW- (UE-A dike), NW to WNW- (UE-C dike), and NE-trending (UE-D and UE-E dikes). These granite dikes are massive, medium-to coarse-grained biotite granites, and their relative ages observed in outcrops are in the order of UE-A, UE-D (=UE-E), and UE-C. The geometric analysis of the dikes indicates that the UE-A and UE-C dikes intrude under approximately NE-SW trending horizontal minimum stress fields. The UE-A dike, which showed a relatively low average SiO2 content by major element analysis, is a product of early magma differentiation compared to other dikes; therefore, it is consistent with the relative age of each dike. The ²⁰⁶Pb/²³⁸U weighted mean ages for each dike obtained from SHRIMP zircon U-Pb dating were calculated to be 167 Ma (UE-A), 164 Ma (UE-C), 167 Ma (UE-D), and 167 Ma (UE-E), respectively. The samples of the UE-A, UE-D, and UE-E dikes showed very similar ages. The UE-C dike shows the youngest age, which is consistent with the results of the relative age in the outcrops and major element analysis. Therefore, the granite dikes intruded into the Middle Jurassic (approximately 167 and 164 Ma), coinciding with those of the Gyeonggi Massif, where the Middle Jurassic plutons are geographically widely distributed. This result indicates that the wide occurrence of the Middle Jurassic plutons on the Gyeonggi Massif was formed as a result of igneous activity moving in the northwest direction with the shallower subduction angle of the subducting oceanic plate during the Jurassic.

• The Journal of the Petrological Society of Korea
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• v.23 no.1
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• pp.17-30
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• 2014

In this study we carried out SHRIMP U-Pb age dating of detrital zircons from age-unknown meta-sedimentary formations distributed around the NNE-SSW trending Gwangju Shear Zone, a branch of Honam Shear Zone, in the southwestern region of the Korean Peninsula. The meta-sedimentary formations from the west (Yeonggwang) and east (Jangseong) areas of the Gwangju Shear Zone have different patterns of zircon age distributions. Zircons of quartzites from the Yeonggwang area yield clusters at Neoarchean (ca. 2,500 Ma), Paleoproterozoic (ca. 1,860 Ma), Neoproterozoic (ca. 960 Ma) and Paleozoic (ca. 380 Ma) ages, but those of the Jangseong area yield clusters at only Neoarchean (ca. 2,500Ma) and Paleoproterozoic (ca. 1,880 Ma) ages. The contrastive patterns in age indicate that the meta-sedimentary formations from the west and east areas correspond to the meta-sedimentary formations of the Okcheon Metamorphic Belt and the sedimentary formations overlying on the Yeongnam Massif, respectively. The results imply that the Gwangju Shear Zone is the tectonic boundary between the Okcheon Metamorphic Belt and the Yeongnam Massif.

• Economic and Environmental Geology
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• v.49 no.2
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• pp.155-165
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• 2016

Quartz schist - quartzite is often intercalated in metasedimentary rocks of Ogcheon belt or aligned parallel to the boundary between Yeongnam massif and Ogcheon belt. However, stratigraphic sequence and or geologic age of the rocks has been still variable among authors as Precambrian or Paleozoic. In this study, we carried out SHRIMP U-Pb age data of detrital zircons from Yeongam and Yeongsanpo areas and compared ours with other zircon ages from other areas. The detrital zircons from the studied area show no age younger than 1.8 Ga but yielded clusters at Neoarchean (2.5 Ga) and Paleoproterozoic (1.8 Ga). On the other hand, the age range of zircon U-Pb dating of Paleozoic quartzites yielded from Archean to middle Paleozoic and clusters at Paleoproterozoic, Neoproterozoic and Paleozoic. The characteristics of the zircon age range and the dominant age peak might become a key to classify the Proterozoic to Paleozoic quartz schists-quartzites, which ages are still remained under controversy. Based on the statistical results of the zircon ages in this study, quartz schist - quartzite from Yeongam and Yeongsanpo is considered to be deposited during Proterozoic.

• The Journal of the Petrological Society of Korea
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• v.20 no.2
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• pp.77-98
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• 2011

The igneous complex consisting of mangerite and gabbro in the Odaesan area, the eastem part of the Gyeonggi Massif, South Korea, intruded early Paleo-proterozoic migmatitic gneiss. The mangerite is composed of orthopyroxene, clinopyroxene, amphibole, biotite, plagioclase, pethitic K-feldspar, quartz. The gabbro has similar mineral assemblage but gabbro has minor amounts of amphibole and no perthitic K-feldspar. The gabbro occurs as enclave and irregular shaped body within the mangerite, and the boundary between the mangerite and gabbro is irregular. Leucocratic lenses with perthitic K-feldspar are included in the gabbro enclaves. These textures represent mixing of two different magmas in liquid state. SHRIMP U-Pb zircon age dating gave $234{\pm}1.2$ Ma and $231{\pm}1.3$ Ma for mangerite and gabbro, respectively. These ages are similar with the intrusion ages of post collision granitoids in the Hongseong (226~233 Ma) and Yangpyeong (227~231 Ma) areas in the Gyeonggi Massif. The mangerite and gabbro are high Ba-Sr granites, shoshonitic and formed in post collision tectonic setting. These rocks also show the characters of subduction-related igneous rock such as enrichment in LREE, LILE and negative Nb-Ta-P-Ti anomalies. These data represent that the mangerite and gabbro formed in the post collision tectonic setting by the partial melting of an enriched lithospheric mantle during subduction which occurred before collision. The heat for the partial melting was supplied by asthenospheric upwelling through the gab between continental and oceanic slabs formed by slab break-off after continental collision. The distribution of post-collisional igneous rocks (ca. 230 Ma) in the Gyeonggi Massif including Odaesan mangerite and gabbro strongly suggests that the tectonic boundary between the North and South China blocks in Korean peninsula passes the Hongseong area and futher exteneds into the area between the Yangpyeong-Odaesan line and Ogcheon metamorphic belt.