[S-SS02] Frontier studies on subduction zone megathrust earthquakes and tsunamis

[SSS02-P06] Clay minerals in the Nankai Trough accretionary sediments as a function of depth

*星野 紘輝¹、金川 久一¹ (1.Department of Earth Sciences, Chiba University)

キーワード：clay minerals, accretionary sediments, Nankai Trough

We investigated how clay minerals in the Nankai Trough accretionary sediments change in content with depth from ≈950 mbsf (meters below seafloor) to ≈3030 mbsf at IODP Site C0002 off Kii Peninsula. Quantitative XRD analyses reveal that the content of smectite relative to total clay minerals decreases with depth from ≈76 wt% to ≈40 wt %, while those of illite and kaolinite increase with depth from ≈10 wt% to ≈30 wt%. Borehole temperature measurement at this Site revealed the temperature at 900 mbsf to be 38 ℃, while the temperature at ≈3000 mbsf has been estimated to be ≈100 ℃ based on the temperature and heat flow data at ≈900 mbsf and logging-while-drilling bit resistivity data. Thus the observed changes in contents of clay minerals likely reflect a temperature increase with depth.