Depositional age of the Lower-Middle Miocene Tanabe Group constrained by detrital zircon U-Pb ages and its implications for stress field

Abe, Noriaki   ; Hoshi, Hiroyuki*; Haji, Toshiki*; Sato, Katsushi*; Niki, Sota*; Hirata, Takafumi*; Iwano, Hideki*; Danhara, Toru*

To constrain the upper limit of the depositional age of the Tanabe Group, Early-Middle Miocene forearc basin deposit, this study obtained the detrital zircon U-Pb ages separated from eight sedimentary rock samples. We obtained 221 concordant ages from 330 zircon grains. The youngest grain age was 19.4 Ma, suggesting the upper limit of the depositional age is younger than 19.4 Ma, and no grain showed the depositional age indicated by foraminifera (16.3-15.1 Ma). Large-scale volcanic activities occurred in the Middle Miocene around Kii Peninsula, mainly after 15 Ma. The lack of grain younger than 15 Ma suggests that the Tanabe Group was deposited before 15 Ma. Sluggish volcanic activities in the provenance areas before 15 Ma may have caused the lack of zircons having ages close to the depositional period inferred from foraminifera.