Fission-track zircon ages of psammitic schist from the chlorite zone of the Sambagawa metamorphic belt, central Shikoku, Japan:

two distinct ages, and implications

Abstract

We analyzed the fission-track (FT) thermochronology of zircon in two samples of psammitic schist from the chlorite zone of the Sambagawa metamorphic belt, central Shikoku, Japan. The samples were collected from the lower-grade part of the chlorite zone (pumpellyite-actinolite facies). Detrital zircons from a single locality along the Asemi River are completely annealed, yielding FT ages of 92.6±6.2 Ma (1σ, 13 grains), and those from a single locality along the Dozan River are also completely annealed, yielding FT ages of 47.2±3.8 Ma (1σ, 7 grains). Although both samples were collected from within the chlorite zone, the two FT zircon ages are different, possibly because they represent the timing of peak metamorphism in the former sample, and a D3 thermal event (post peak-metamorphism) in the latter sample.