Plate interface shear zone discovered in the Sanbagawa metamorphic belt of Japan

The study of deformation in exhumed subduction zones is of paramount importance to understand the earthquake cycle and associated deep processes in the Earth’s crust.

An Italian-Japanese research team investigated a river valley in the Sanbagawa Belt on the Island of Shikoku, where originally subducted metamorphic rocks are exposed at depths of 30 to 40 km. 

Multiple analytical techniques coupled with classic structural-petrographic analysis, have been used to extract information on portions of polyformed metamorphic rocks. 

Thanks to the application of RSCM thermometry on carbonaceous matter, geochronology of zircons, and thermodynamic modelling of mineral parageneses, has been discovered a hidden shear zone that was active during exhumation of deeply subducted rocks on top of subducting sediments. This study paves the way for future investigations of subduction zone processes in SE Japan.

Bibliographic reference

Papeschi, S., Kawaguchi, K., Okazaki, K., Hayasaka, Y., & Hirose, T. (2025). Plate Interface Shear Zone in the Sanbagawa Metamorphic Belt, Constrained by RSCM Thermometry, U–Pb Zircon Dating and Phase Equilibria Modelling in the Sarutagawa Region, Central Shikoku, Japan. Journal of Metamorphic Geology. Doi: https://doi.org/10.1111/jmg.12807.

For information: Samuele Papeschi, CNR-IGG (samuele.papeschi@igg.cnr.it).