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Strike-parallel variations in clay minerals and fault vergence in the Cascadia subduction zone

¹ Department of Geological Sciences, University of Missouri, Columbia, Missouri 65211, USA

Clay minerals probably affect the zonation of mechanical properties within a thick unit of abyssal-plain deposits as they enter the Cascadia subduction zone. Landward- vergent thrust faults develop above a deeper décollement because smectite-rich mudrocks within that corridor release more water during clay dehydration, which in turn elevates pore pressure and reduces basal shear stress relative to wedge strength. Conversely, dilution of smectite by illite and chlorite increases the frictional coefficient, and fluid overpressure should drop where smectite dehydration is volumetrically reduced. Thus, thrust faults within chlorite-rich segments of the margin are seaward vergent.

Key Words: Cascadia subduction zone • Ocean Drilling Program • clay minerals • smectite • faults

This article has been cited by other articles:

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