1:45 PM - 3:15 PM
[SCG52-P17] Thermal structure of the Nankai inner accretionary wedge estimated from vitrinite reflectance of the cuttings sampled during IODP Expedition 358
Keywords:Nankai Trough, Accretionary wedge, Drilling
The temperature of the subduction zone is one of the important physical basic information for understanding the earthquake activity and material circulation in the subduction zone. The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE), which was conducted as part of the international Ocean Discovery Program (IODP) to understand the earthquake generation mechanism and the propagation of the destruction along the plate boundary fault in the Nankai Trough, has the deepest borehole that has been carried out since October 7, 2018. The samples used in this research were obtained during the IODP Expedition 358.
During the IODP Expedition 358, drilling was conducted from the seafloor to 3262.5 m below seafloor (mbsf) at Site C0002, located in the inner wedge of the accretionary prism, off-Kii Peninsula, and in the Kumano Basin. The age of the accretionary prism sediment ranges between 10.5-7.09 Ma, as determined by the calcareous nannofossil biostratigraphy (Kitajima et al., 2019). The cuttings were continuously collected, and the vitrinite reflectance (Ro) was measured at Yamaguchi University after separating the carbonaceous materials from the cuttings.
The mode of Ro, which was in the range of 0.38-0.59%, was adopted because Ro is not normally distributed. Ro values increase with depth and are slightly higher than those of IODP Expedition 348 (870.5-3058.5 mbsf). The temperatures estimated by the Easy%Ro (Sweeny and Burnham 1990) assuming the heating time as the depositional age showed a range of 75-115 °C for the mode value. The temperatures converted from the Ro mean values are in almost good agreement with the values reported by Sugihara et al. (2014).
During the IODP Expedition 358, drilling was conducted from the seafloor to 3262.5 m below seafloor (mbsf) at Site C0002, located in the inner wedge of the accretionary prism, off-Kii Peninsula, and in the Kumano Basin. The age of the accretionary prism sediment ranges between 10.5-7.09 Ma, as determined by the calcareous nannofossil biostratigraphy (Kitajima et al., 2019). The cuttings were continuously collected, and the vitrinite reflectance (Ro) was measured at Yamaguchi University after separating the carbonaceous materials from the cuttings.
The mode of Ro, which was in the range of 0.38-0.59%, was adopted because Ro is not normally distributed. Ro values increase with depth and are slightly higher than those of IODP Expedition 348 (870.5-3058.5 mbsf). The temperatures estimated by the Easy%Ro (Sweeny and Burnham 1990) assuming the heating time as the depositional age showed a range of 75-115 °C for the mode value. The temperatures converted from the Ro mean values are in almost good agreement with the values reported by Sugihara et al. (2014).