Search

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]

Abstract: We report the Sr, Nd and Pb isotopic ratios of clinopyroxene separates from spinel peridotite xenoliths hosted by late Cenozoic alkali basaltic rocks from Baengnyeong Island, Jogokni, and Jeju Island, all near the southeastern margin of the Sino-Korean Craton in South Korea. Measured Sr, Nd and Pb isotopic compositions in the clinopyroxene separates show, in general, simple trends between depleted MORB-like mantle (DMM) and relatively enriched components, which can be explained by old event(s) of infiltration by metasomatic melts/fluids that enriched a precursor time-integrated depleted mantle in incompatible trace elements and overprinted its isotopic composition. Comparison of the xenoliths with the host basalts suggests that infiltration of carbonatitic melts can explain the characteristics of the Baengnyeong xenoliths while reaction with residual slab-derived melt/fluid subjected to amphibole and phlogopite fractionation explains the Jogokni xenoliths best, ruling out direct influence of the magmatism that produced the host basalts. On the other hand, the Jeju clinopyroxene separates display a mixing hyperbola between DMM and the host basalts in Sr–Pb and Nd–Pb isotope correlation diagrams, suggesting some influence by liquids similar to the host basalts. The Korean xenoliths tend to be similar in the overall range of their mineralogic modes, elemental compositions, and Sr–Nd–Pb isotopic ratios to those of the fertile peridotite xenoliths derived from the post-Archean lithospheric mantle of eastern China, and yet without any compositional evidence for a refractory Archean mantle root. Overall comparison of the measured isotopic compositions for these Korean xenoliths with available data on lavas from eastern China, indicates that the dominant enriched mantle source components for the Cenozoic intraplate volcanism in the East Asia (EM1 for northeast China, and EM2 for Southeast Asia) are absent in the lithospheric mantle beneath the region. The Cenozoic intraplate volcanism, therefore, must have originated in the asthenosphere. [Copyright &y& Elsevier]