• Economic and Environmental Geology
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• v.25 no.4
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• pp.435-446
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• 1992

REE, major and trace elements analyses of the Jurassic Daebo granite and Cretaceous Bulguksa granite were carried out to interpet their petrogenesis and relationships between petrogenesis and tectonics. Analytical results are summarized as follows. (1) $SiO_2$ content of the Bulguksa granite (aver. 74.6%) are significantly higher than those of the Daebo granite (aver. 68.1%). Major elements of $TiO_2$, $Al_2O_3$, $P_2O_5$, CaO, MgO, Total FeO, and trace elements of Co, V and Sr are negatively correlated with $SiO_2$. Incompatible elements such as Ba, Sr, Y, Zr and HREE are contained differently in the Bulguksa granites distributed in between Okchon folded belt and Kyongsang sedimentary basin. (2) Trace element abundances show a good discrimination between two goups of granitic rocks. Ba, Sr and V are enriched in Daebo granites, while Zn and Cr are depleted in them. (3) Jurassic granites have quite different Eu anomalies and REE patterns from those of Cretaceous granites: Large negative Eu anomaly in the former and mild or absent Eu anomaly in the latter. The large Eu negative of Cretaceous granitic rocks are interpreted as a differentiated product of fractional crystallization of granitic magma from the upper mantle. Meanwhile, the Daebo plutonic rocks was resulted from the partial melting of subcrustal material or crustal contamination during ascending granitic magma from the mantle. Senario of igneous activities of Mesozoic age in South Korea was proposed based on Kula-Pacific ridge subduction model.

• The Journal of the Petrological Society of Korea
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• v.23 no.3
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• pp.279-292
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• 2014

Nd isotopic compositions analyzed from the Phanerozoic granitoids of Korea are integrated and discussed. Variations in Nd isotopic compositions can be explained either by temporal trend or by regional differences. Among the three active periods, first two periods during the Permian-Triassic and Jurassic seem to show variations from rather high ${\varepsilon}_{Nd}(t)$ values at the beginning to lower ${\varepsilon}_{Nd}(t)$ values during the later stages. Such trends probably reflect melting of the subducting oceanic crust and producing magma with higher proportion of depleted mantle derived materials during the early stage of subduction process, and subsequent magmas with greater proportion of old continental crust with progress of subduction. However, the Cretaceous-Paleogene period of active magmatism displays higher ${\varepsilon}_{Nd}(t)$ values during the advanced stage of the igneous activities, which is opposite to the previous active periods. The other explanation is that such differences in ${\varepsilon}_{Nd}(t)$ reflect regional differences, based on the observations that such high-${\varepsilon}_{Nd}(t)$ granitoids distribute in the northeastern Gyeongbuk Province and Gyeongsang Basin. If this is the case, the regions with highr ${\varepsilon}_{Nd}(t)$ values may have distinct crustal evolution histories, e.g. younger average age. The choice between the two hypothesis could be made through further studies.