Slipped deformation bands: A new type of cataclastic deformation bands in Western Sinai, Suez rift, Egypt

Abstract

A type of cataclastic deformation band that features a central discrete slip surface within separate, individual bands is described. Slip surface development is normally constrained to the eventual brittle failure of a deformation band cluster zone due to strain hardening and sequential growth of deformation bands. The deformation bands described herein deviate from this model and, in comparison with classical cataclastic deformation bands previously described in the literature, feature more intense cataclasis, higher offsets, lower permeability but higher porosity. We present evidence suggesting that the bands of this study strain soften during their evolution. Thus, they can accumulate higher strains than classical cataclastic bands and are prone to be reactivated during progressive deformation. The bands appear to have formed under simple shear with minor compaction, following an evolution of (1) band nucleation by grain fracturing and crushing, (2) progressive cataclasis, (3) nucleation of a central fracture, and (4) slippage along the fracture – the end result is referred to as a ‘slipped deformation band’. Widespread background, intragranular fracturing of the host rock and relatively high porosity in the bands are suggested as the most probable causes of deviation from traditional models for tectonic deformation in high porosity sandstones.