Spatial distributions of low-temperature thermochronometric data in Shikoku mountains and these interpretations

Fukuda, Shoma   ; Okamoto, Akira*; Kohn, B.*; Shinjo, Hironao*; Sueoka, Shigeru   ; Tagami, Takahiro*

The Shikoku Mountains are a non-volcanic uplift zone parallel to the subduction zone of the Philippine Sea Plate, and elucidation of its mountain building process is expected to contribute to constraining the long-term strain accumulation and release mechanism in the Nankai Trough. In this study, we attempted thermochronological analysis of nine granitoids of the Permian to Miocene age in the Shikoku Mountains using apatite and zircon (U-Th)/He (AHe, ZHe) and apatite fission-track (AFT) methods, which can provide thermal and exhumation history in the shallower crust (2 to 6 km depth). AHe and ZHe dating was conducted at the University of Melbourne, and AFT dating at the Tono Geoscience Center. AHe ages for eight samples ranged from about 55 to 7 Ma, AFT ages for five samples ranged from about 90 to 70 Ma, and ZHe ages for nine samples ranged from about 200 to 70 Ma. These data showed a consistent relationship considering the closure temperature of each method. They are also generally consistent with previously reported ZFT ages, biotite K-Ar ages, and AHe, AFT, and ZHe ages.