Zircon U-Pb ages of Cretaceous intrusive rocks in Central Yamaguchi, Southwest Japan: Implications for an enriched mantle source during a magmatic flare-up

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  • OWADA Masaaki
    Division of Earth Sciences, Graduate School of Science and Technology for Innovation, Yamaguchi University
  • KODAMA Shogo
    Taiheiyo Consultant, West Japan Technology Center
  • NAGASHIMA Mariko
    Division of Earth Sciences, Graduate School of Science and Technology for Innovation, Yamaguchi University
  • NAKANO Nobuhiko
    Division of Earth Sciences, Faculty of Social and Cultural Studies, Kyushu University
  • ADACHI Tatsuro
    Division of Earth Sciences, Faculty of Social and Cultural Studies, Kyushu University

Bibliographic Information

Published
2026
DOI
  • 10.2465/jmps.251128cl
Publisher
Japan Association of Mineralogical Sciences

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<p>Zircon U-Pb dating was conducted on granite, granodiorite, and gabbro from the central part of Yamaguchi Prefecture, Southwest Japan. The granodiorite and gabbro are recognized as components of the Susuma-Nagaho Plutonic Complex (SNPC). The zircon U-Pb dating yielded ages of 103 Ma for the granite and 92 Ma for the granodiorite and gabbro. These ages coincide with the magmatic flare-up event documented in Southwest Japan. A compiled dataset of Cretaceous gabbro-diorite from Southwest Japan shows that initial-εNd values (εNdI) decrease progressively to as low as −5.1 between 107 and 90 Ma. In addition, Th/La ratios exhibit a negative correlation with initial-Nd isotopic ratios. These geochemical trends, together with their temporal variation, suggest that subducted sediments increasingly interacted with the mantle wedge, producing progressively enriched mantle sources throughout the Cretaceous. This secular change may reflect variations in plate motion, such as change in the rate of subduction.</p>

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