Ductile strains in clay-rich sediments from Hole 808C: preliminary results using X-ray pole figure goniometry

Abstract

Deformation within accreting and subducting sediments may occur through ductile as well as brittle modes, producing deformation fabrics defined by the preferred orientation of sedimentary particles. The method of X-ray pole figure goniometry is used to determine the clay-mineral fabric in hemipelagic sediments collected from Hole 808C within the Nankai accretionary prism toe during ODP Leg 131. The resulting strains, adjusted to reflect volume changes in the sediments, suggest that accreting sediments have experienced up to 10% lateral ductile shortening while subducting sediments show little evidence for any lateral shortening. This suggests that the decollement serves as an important boundary between subducting and accreting sediments in the vicinity of Site 808. Vertical strains obtained here are lower than expected, especially for the deepest samples, possibly due to the effects of bioturbation during primary deposition and compaction, or to the breakdown of the March model at high strains. -from Authors