How pressure-solution enables the development of deformation bands in low-porosity rocks

Abstract

Occurrence of deformation bands developing with various orientations in a low-porosity bioclastic calcarenite in the Cotiella Massif (Spanish Pyrenees), questions about the mechanism responsible for their generation in low-porosity carbonates. Our work is based on the combination of a 2D and 3D petrographic and microstructural study, using electron backscattering diffraction microscopy and X-ray microtomography, with a diagenetic study, using cathodoluminescence microscopy and scanning electron microscopy images. Diagenetic and petrographic observations indicate early cementation, which led to significant porosity reduction prior to a sequence of deformation processes comprising the development of tectonic stylolites around which deformation bands eventually formed. Along the latter, quartz grains appear fractured with high strain patterns, showing a different appearance compared to the quartz along the stylolite. Moreover, the ratio of carbonate matrix versus quartz grains shows distinctive variations throughout the different stages of deformation. Based on these observations, we propose a conceptual model for the genesis of deformation bands in low-porosity rocks, accounting for the preferential dissolution of calcite with respect to quartz grains along the stylolite plane that resulted in local porosity development in between quartz grains. Consequently, quartz aggregation led to the classical deformation band mechanism of strain accumulation and breakage.