This study presents sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon ages, and whole-rock chemical and isotopic (Sr-Nd) compositions of representative Triassic plutons from South Korea. The plutons from the Gyeonggi massif (Hongseong, Namyang, Yangpyeong and Odesan), the central Okcheon belt (Baeknok and Yongsan), and the Yeongnam massif (Sangju, Gimcheon, Hamyang and Macheon) yield zircon U-Pb ages of ca. 232-226Ma, 227-226Ma, and 240-228Ma, respectively. Among the Triassic plutonic suite in South Korea, those within the Gyeonggi massif are dominated by granite, syenite, monzonite, monzodiorite and gabbro. Plutons within the Okcheon belt are mainly by granite to quartz monzodiorite. The Yeongnam massif mainly incorporates granite to granodiorite and minor monzodiorite intrusions. The geochemical signatures of the Triassic plutons are characterized by Ta-Nb troughs, depletion of P and Ti, and enrichment of LILE. Most plutons except Macheon monzodioritic pluton show high initial 87Sr/86Sr ratios (0.708248-0.714678) and strongly negative εNd(T) (-20.3 to -7.7) values, suggesting contribution from middle to upper crust. In contrast, the Macheon monzodioritic pluton in the Yeongnam massif shows relatively low initial 87Sr/86Sr ratios (0.706547-0.706629) and negative εNd(T) (-4.43 to -3.62) values. The Middle Triassic syenite-monzonite-granite-gabbro series in and around the Gyeonggi massif possess high-K calc-alkaline and shoshonitic affinity suggesting a post-collisional magmatic event following the Permo-Triassic collision between the North and South China blocks. The Triassic plutons in the Yeongnam massif and the Okcheon belt, together with a Permian Yeongdeok pluton in the Gyeongsang basin, show features typical of high- to medium-K calc-alkaline magmatism with LREE and LILE enrichments. This together with a depletion of Y and HREE suggests their formation in a subduction setting. Our results provide robust evidence to consider the Gyeonggi massif as an extension of the Qinling-Dabie-Sulu belt between the North and South China blocks in central China. The Okcheon belt and Yeongnam massif in South Korea, together with the continental margin of South China, are marked by a common Permian to Triassic magmatic episode, probably related to the paleo-Pacific slab subduction.
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We thank Dr. Yener Eyuboglu and an anonymous reviewer for constructive reviews. This work was supported as a Basic Research Project ( GP2009-012 ; Tectonic evolution of major crustal units in the mid-western part of the Korean peninsula) of the Korea Institute of Geoscience and Mineral Resources (KIGAM), funded by the Ministry of Knowledge Economy, Korea to S.W. Kim. This work was supported by the Korea Meteorological Administration Research and Development Program under Grant Number CATER 2011-5120 to S. Kwon.
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