Geothermal structure of the Miura-Boso plate subduction margin, central Japan

We have constrained the geothermal structure of the Miura-Boso plate subduction margin, located in central Japan, using maximum paleo-temperature data derived from vitrinite reflectance measurements. We established that higher maximum paleo-temperatures are restricted to the western part of the early Miocene Hota accretionary complex (Hota and Hayama groups), indicating a spatial difference in the amount of slip upon the out-of-sequence thrust potentially associated with the Izu-Bonin Island Arc collision. The weakly deformed sedimentary sequences overlying the highly deformed Hota Group strata have much lower vitrinite reflectance values than the latter. This variation indicates that the sedimentary sequences of the trench slope experienced a markedly lower maximum burial depth than the relatively deep-buried and uplifted Hota accretionary complex. Conversely, maximum paleo-temperatures obtained for tectonic blocks hosted by the neighboring Mineoka ophiolite complex are very high: ca. 140 °C for the large, early Miocene Haccho Formation blocks, and 65-90 °C for the other blocks. This result suggests that the individual tectonic blocks enclosed in the ophiolite complex were subjected exhumation from depths of 3-5 km.