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NE trending granitoid batholiths in South Korea are part of the huge Phanerozoic granitoid belt in east Asia. The crystallization ages of granitoid plutons show three episodes of Mesozoic magmatism in South Korea: Triassic (248-210 Ma), Jurassic (197-158 Ma), and Late Cretaceous-early Tertiary (110-50 Ma), with a Late Jurassic-Early Cretaceous (∼50 m.y.) hiatus. The granitoid ages and kinematic analyses of the Mesozoic structures in South Korea suggest that the Middle Jurassic (180-170 Ma) dextral strike-slip ductile shear zones formed by the northwest (orthogonal) subduction of the Izanagi plate, whereas the Cretaceous sinistral faults formed by the northward (oblique) subduction of the same plate, which generally agree with proposed reconstruction of plate motions, albeit uncertain, around east Asia. Among the models proposed to explain magmatic lull in a continental arc, shallow angle subduction associated with high convergence rate and subduction of oceanic plateaus might be the probable cause for the magmatic hiatus in South Korea and Japan. The huge width (∼500 km) of the east Asian granitoid belt may be explained by oceanward retreat of subduction zone in the Cretaceous in association with change in the movement direction of the subducting plate. [ABSTRACT FROM AUTHOR]

Abstract We present chemical and Sr–Nd–Pb isotopic compositions of three Triassic (226–241 Ma) calc-alkaline granitoids (the Yeongdeok granite, Yeonghae diorite and Cheongsong granodiorite) and basement rocks in the northern Gyeongsang basin, south-eastern Korea. These plutons exhibit typical geochemical characteristics of I-type granitoids generated in a continental magmatic arc. The Yeongdeok and Yeonghae plutons have similar initial Sr, Nd and Pb isotope ratios (87 Sr/86 Srinitial = 0.7041 ~ 0.7050, ℇNd (t) = 2.3 ~ 4.0, 206 Pb/204 Pbfeldspar = 18.22 ~ 18.34), but distinct rare earth element patterns, suggesting that the two plutons formed from partial melting of a similar source material at different depths. The Cheongsong pluton has slightly more enriched Sr–Nd–Pb isotopic compositions (87 Sr/86 Srinitial = 0.7047 ~ 0.7065, ℇNd (t) = 3.9 ~ 2.8, 206 Pb/204 Pbfeldspar = 18.24 ~ 18.37) than the other two plutons. The Nd model ages of the basement rocks (1.1 ~ 1.4 Ga) are slightly older than those of the plutons (0.6 ~ 1.0 Ga). The initial Sr and Nd isotopic ratios of the plutons can be modeled by the mixing between the mid-oceanic ridge basalt-like depleted mantle component and the crustal component represented by basement rocks, which is also supported by Pb isotope data. The Sr and Nd isotope data from granitoids and basement rocks suggest that the Gyeongsang basin, the Hida belt and the inner zone of south-western Japan share relatively young basement histories (middle Proterozoic), compared with those (early Proterozoic to Archean) of the Gyeonggi and Yeongnam massifs and the Okcheon belt. The Nd isotope data of basement rocks suggest that the Hida belt might be better correlated with the basement of the Gyeongsang basin than the Gyeonggi massif, the Okcheon... [ABSTRACT FROM AUTHOR]