Zircon U[sbnd]Pb[sbnd]Hf and geochemical analyses of paragneiss and granitic gneiss from Oki-Dogo Island, Southwest Japan and its tectonic implications

Abstract

The paragneiss and migmatitic gneiss on Oki-Dogo Island, located in northern part of southwest Japan, have UPb ages ranging from Mesoarchean to Paleoproterozoic. The youngest population of detrital zircons from the paragneiss and migmatitic gneiss suggests a maximum depositional age of ca. 1.96 Ga. Further, the three granitic gneiss samples give zircon UPb ages of 1.97, 1.88, and 1.81 Ga. The bulk rock composition of the granitic gneiss samples followed a calc-alkaline trend and showed negative Nb, Ta, P, and Ti anomalies with low Sr/Y (<35), Nb/Th (<1), and Nb/Zr (<0.1) ratios, indicating that the protolith of the granitic gneiss formed in an arc-related setting. Zircons from the granitic rocks in Oki-Dogo Island have negative εHf(t) values with Mesoarchean to Neoarchean model ages (TDM2). The results of geochronological and geochemical analyses and those of previous studies indicate that Oki-Dogo Island underwent two arc-related magmatic events at ca. 1.97 Ga and ca. 1.88–1.81 Ga, which correspond well with those of the Yeongnam massif in South Korea. Thus, we suggest that northern part of southwest Japan (Oki-Dogo Island) was more closely related with the Yeongnam massif than with the North China Craton during the early Paleoproterozoic period.