Cataclastic deformation of triaxially deformed, cemented mudrock (Callovo Oxfordian Clay): an experimental study at the micro/nano scale using BIB-SEM
Guillaume Desbois1, Nadine Höhne1, Janos L. Urai1, Pierre Bésuelle2, and Gioacchino Viggiani31Structural Geology, Tectonics and Geomechanics, RWTH Aachen University, Lochnerstrasse 4–2, 52056 Aachen, Germany 2CNRS, 3SR, Grenoble, France 3Université Grenoble Alpes, 3SR, Grenoble, France
Received: 12 Sep 2016 – Accepted for review: 30 Sep 2016 – Discussion started: 04 Oct 2016
Abstract. The macroscopic description of deformation and fluid flow in mudrocks can be improved by a better understanding of microphysical deformation mechanisms. Here we use a combination of Scanning Electron Microscopy (SEM) and Broad Ion Beam (BIB) polishing to study the evolution of micro structure in samples of Callovo-Oxfordian Clay that were previously tested in the lab. Digital Image Correlation (DIC) enabled for the measurement of strain fields in the specimens, which were used as a guide to select regions in the sample for BIB-SEM analysis. Microstructures show evidence for dominantly cataclastic mechanisms (intergranular, transgranular, intragranular cracking, grain rotation, clay particle bending) down to nm- scale. At low strain, the dilatant fabric contains individually recognizable open fractures, while at high strain the reworked clay gouge contains broken non-clay grains, with a clear change towards smaller pores than the undeformed material and corresponding resealing of initial fracture porosity.
This study might provide a first step towards a micro scale basis for constitutive models of deformation and fluid flow in cemented mudstones.
Desbois, G., Höhne, N., Urai, J. L., Bésuelle, P., and Viggiani, G.: Cataclastic deformation of triaxially deformed, cemented mudrock (Callovo Oxfordian Clay): an experimental study at the micro/nano scale using BIB-SEM, Solid Earth Discuss., doi:10.5194/se-2016-131, in review, 2016.