Detrital Zircon Age Spectra of the Upper Cretaceous Atogura and Tochiya Formations in the Northern Kanto Mountains, SW Japan

Abstract

The overall configuration of the Cretaceous subduction-related arc-trench system in Japan is preserved in the current distribution of the relevant orogenic components; i.e., the coeval set of accretionary complexes formed at the trench （Sanbosan and North Shimanto belts） , high-P/T meta-ACs along the Wadati-Benioff zone （Sanbagawa and Shimanto metamorphic belts） , arc batholiths （Ryoke-Sanyo and San-in belts） , and fore-arc basin strata （Ryoseki-Monobegawa and Izumi groups） . To document the sediment distributary pattern within the Cretaceous arctrench system and the composition of relevant provenance, detrital zircon dating was conducted for the Upper Cretaceous sandstones （Atogura and Tochiya formations） from the northern Kanto Mountains. These strata occur immediately to the south of Median Tectonic Line of SW Japan, and as klippe with unknown origin. The results of U-Pb dating by LA-ICPMS show that three sandstones have common age spectra with four major age groups; i.e., 120-150 Ma （Early Cretaceous） , 170-200 Ma （Jurassic） , 250-300 Ma （Permian） , and 1600-2200 Ma （Paleoprotero-zoic） , with minor amounts of much older grains up to 2900 Ma （Archean） . These age spectra are unique, when compared to other coeval Cretaceous fore-arc and/or intra-arc sandstones in Japan. The Early Cretaceous grains were obviously derived from a proximal source to the depositional site, probably the Cretaceous volcanic arc of the Ryoke-Sanyo belt in SW Japan. The dominant grains of the Jurassic and Permian ages were probably derived from coeval plutonic belts in the provenance, whereas the Paleoproterozoic grains were probably derived from continental blocks in East Asia with crusts of corresponding ages, such as the North and South China blocks. Except for the Cretaceous arc source, Jurassic and Permian granitoids are extremely rare in

SHRIMP U–Pb ages of detrital zircons from the Early Cretaceous Nakdong Formation, South East Korea: Timing of initiation of the Gyeongsang Basin and its provenance

“…The gray section is known as the magmatic quietscent period (Sagong et al, ). Data are compiled from the literatures (Aoki et al, , , ; T. Choi, Lee, & Orihashi, ; Kawagoe et al, ; J. Kim, Cho, Kim, & Son, ; T. Lee, et al, 2010, 2015; Y. Lee et al, 2010; Maki et al, ; Nakahata, Isozaki, Kosaka, Sakata, & Hirata, ; Nakahata, Isozaki, Tsutsumi, & Iwamoto, ; Okawa et al, )…”