Evolution of the Sanbagawa and Shimanto high-pressure belts in SW Japan: Insights from K–Ar (Ar–Ar) geochronology

摘要: Abstract The Sanbagawa belt sensu lato in Japan is one of the world’s classical high-pressure (HP) metamorphic belts and has long been considered to be a coherent HP Cretaceous age. However, recent progress detrital zircon geochronology together with accumulation abundant phengites K–Ar (Ar–Ar) ages revealed that comprised two petrotectonic belts—Sanbagawa stricto Shimanto belt. These have distinctly different peak metamorphism P–T conditions metamorphism. schists were metamorphosed pumpellyite–actinolite facies through epidote-blueschist epidote–amphibolite up eclogite during prograde stage subduction zone at 120–115 Ma. Phengite subsequent exhumation after took placed manner higher-grade rocks exhumed more rapidly comparison lower-grade rocks; this supported by positive correlation between age apparent gradient formed post-metamorphic hydration/recrystallization. Moreover, experienced intense ductile deformation long-term exhumation; it longer than 31 m.y. reset phengite system. In contrast, epidote-blueschist/greenschist transitional short-term for less 13 m.y. This short negative gradient. contrasting age-temperature relationships suggest processes belts, most likely due change subducting oceanic plates along paleo-Japanese convergent margin.