Characteristics of Nd Isotopic Compositions of the Phanerozoic Granitoids of Korea and Their Genetic Significance

Abstract

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 ε Nd (t) values at the beginning to lower ε 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 ε 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 ε Nd (t) reflect regional differences, based on the observations that such high-ε Nd (t) granitoids distribute in the northeastern Gyeongbuk Province and Gyeongsang Basin. If this is the case, the regions with highr ε 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.

Detrital Zircon U-Pb Geochronology and Hf Isotope Geochemistry of the Hayang Group, SE Korea and the Himenoura and Goshoura Groups, SW Japan: Signs of Subduction-Related Magmatism after a Long Resting Period

“…Hf isotopic compositions of the detrital zircons are also helpful in tracking the provenance of sediments. The ε Hf (t) values of the Jurassic and Triassic zircons of the Hayang Group ranges from −18.2 to −5.4 and agree well with typical values for Jurassic and Triassic granitoids known in South Korea [59,60]. The Paleoproterozoic and Archean zircons of the Hayang Group have ε Hf (t) values of −14.8 to +6.9 and are similar to the Paleoproterozoic basement rocks of the Yeongnam massif surrounding the Gyeongsang basin [54,61].…”