[SSS04-P16] Connecting faults and fractures with clay formation and fluid movement in the accretionary prism of the Nankai Trough: NanTroSEIZE IODP Expeditions 338/348, Site C0002
Keywords:Nankai Trough Seismogenic Zone, Clay-fluid interaction, Accretionary prism, Borehole imaging, Logging while drilling
The main focus of this contribution is on the analysis and potential link between structure development and the associated formation of clay minerals in the accretionary prism. We analyzed the relationship between the fractures, faults and the changes in clay mineralogy as derived from post-cruise cutting sample analyses. The comparative analysis of clay mineralogy reveals an increase of intensity observable in smectite and illite at specific depth intervals that are related to fault and fracture zones at 2350-2400 mbsf, at 2600-2800 mbfs, and also at 2150 mbsf. This increased intensity reflects an increase in the amount of smectite and illite in those areas, that could be related to due to abundant fluid-rock interaction processes. The connection between structures characterized on borehole images and the changes in clay mineralogy for Hole C0002P suggests that mineralogical changes are associated to structures of the Nankai accretionary prism. This is critical for a better understanding of clay-fluid interaction and mechanical properties during fault displacements and seismogenesis. We interpret a defined connection between the occurrence of fracture and/or faults in the accretionary prism and the abundance of illite and smectite clay minerals. Ongoing postcruise research on hole C0002 N and C0002P (Expedition 348) should confirm these results.
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