Sedimentary history and provenance analysis of the Sanbagawa Belt in eastern Kii Peninsula, Southwest Japan, based on detrital zircon U–Pb ages

Abstract

U–Pb isotope ages of detrital zircons from psammitic rocks of the Sanbagawa Belt in eastern Kii Peninsula, Japan, were determined by laser ablation–inductively coupled plasma–mass spectrometry. The age spectra patterns allow four sedimentary types to be distinguished on the basis of dominant zircon age proportions: Permian–Jurassic, Cretaceous, Precambrian and Mixed types. Combining the age data with geological features in the area, we subdivide this belt into the Mayoidake, Hachisu, Kayumi, and Haze complexes, with their deposition–accretion ages estimated as 116–95, 103–84, 98–76, and 76–73 Ma, respectively. The Mayoidake Complex is dominated by Permian–Jurassic-type sediments, whereas the Haze Complex is dominated by Precambrian-type sediments. Cretaceous-type and Mixed-type sediments are found in the Kayumi and Hachisu complexes. Most of the Cretaceous zircons are inferred to have been derived from a Late Cretaceous volcanic arc on the eastern margin of the Eurasian continent, whereas the Precambrian zircons are interpreted to have been sourced from basement of the North China Block. By also considering results of previous studies, we conclude that the Mayoidake Complex belongs to the neighboring Shimanto Accretionary Complex rather than the Sanbagawa Metamorphic Rocks. Furthermore, detrital zircon U–Pb age spectra for the interval 100–95 Ma differ between the Mayoidake and Hachisu complexes. This difference suggests that the depositional basin of the Sanbagawa Metamorphic Rocks was separate and lay some distance from that of the Shimanto Accretionary Complex, with the two belts finally being juxtaposed by lateral displacement along a steeply dipping strike-slip.