[3poster47-56] R14 [Regular Session]Tectonics

[R14-P-4] (entry) Late Permian tectonic switch in Maizuru terrane: Evidence from U-Pb detrital zircon geochronology from Tonoshiki Formation

*Larissa NGOMBI MAVOUNGOU¹, Kaushik DAS^1,2, Yasutaka HAYASAKA^1,2, Kenta KAWAGUCHI³ (1. Department of Earth and Planetary Systems Science, Hiroshima University, 2. Hiroshima Institute of Plate Convergence Region Research, Hiroshima, 3. Department of Earth and Environmental Sciences, Jeonbuk National University, Republic of Korea)

Keywords:Late Permian, Maizuru back-arc basin, Maizuru terrane, Tectonic and provenance switch, Tonoshiki breccia, Tonoshiki Formation

Tonoshiki Formation (TF) deposited in Maizuru back-arc basin (Mz.BAB) which closed during Late Permian (Hayasaka et al.,1996). It is a breccia-dominated unit occurring exclusively in the central zone of Maizuru terrane (Mz.T). The breccia was so far described as mostly made up of Yakuno ophiolitic mafic rocks clasts-derived materials, suggesting its deposition directly on top of Early Permian Yakuno Ophiolite (Tokuoka et al., 1987). Here, we report new petrological characteristics, revealing the presence of felsic shallow crustal blocks in Tonoshiki breccia (TB). These different types of TB might have deposited at different ages. A proper constraint on the sedimentation age of TF and surrounding rocks is important to understand its evolution in Mz.BAB. The U-Pb detrital zircon geochronology conducted on 2 samples of TB yielded 2 dominant probability peaks at 275 and 268 Ma for the mafic rock clasts-rich unit and the felsic crustal material-dominated type, respectively. This suggests two major possible sources for TB. Major source provenance of mafic rock clasts-rich breccia is considerably the Yakuno ophiolite of southern zone where the mafic-dominant island arc magmatism occurred during ~285¬-275 Ma (Herzig et al., 1997). Whereas the crusts of felsic materials-dominated unit were possibly sourced from the East Asian continental arc of northern zone of Mz.T, such as the Korean Peninsula where the Permian arc-magmatism initiated at ~272 Ma until Late Triassic (Kim et al., 2021). TB possibly formed by debris flow during two episodes of tectonic activity occurring in and around Mz.BAB. The detrital zircon data obtained from 3 samples of sandstone outcroping in Mz.BAB showed different age populations with 3 major probability peaks at 275, 269, and 268 Ma. The breccia and sandstone samples revealed Latest Permian maximal depositional ages. The Latest Permian sedimentation in Mz.BAB was characterized by the deposition of coarse-grained material, sandstone and collapse breccia, supplied from both southern and northern zone of Mz.T, implying a switch of provenance and intense tectonic activity that affected Mz.BAB before its closure.

Hayasaka et al. (1996) Tectonics and Metamorphism.
Herzig et al. (1997) Island Arc.
Kim et al. (2021) Gond. Res., in press.
Tokuoka et al.(1987) In Memoir of the Fac. of Sci. Shimane Univ.