Microstructural Analysis of Deformation Bands from Site 860, Chile Margin

Abstract

Deformation bands, with good macroscopic and microscopic indicators of shear are the clearest macroscopic manifestation of accretionary deformation from ODP Site 860. Backscattered electron SEM studies of deformation bands show that these structures are characterized by low porosity, an increase in matrix:grain ratios and grain-size reduction. Locally grain alignment fabrics are observed and some deformation bands show evidence of injection of foreign material and diagenetic changes. Strain magnitudes from space and shape fabrics are small, both inside and outside deformation bands. We propose that deformation bands develop during transient cycles of dilation, shear and fluid flow associated with accretionary deformation.