Lessons Learned from Electron Microscopy of Deformed Opalinus Clay

• Published in: Advances in Laboratory Testing and Modelling of Soils and Shales (ATMSS) pp. 345 - 350
• Main Authors: Laurich, Ben, Urai, Janos L., Desbois, Guillaume, Klaver, Jop, Vollmer, Christian, Nussbaum, Christophe
• Format: Book Chapter
• Language: English
• Published: Cham Springer International Publishing
• Series: Springer Series in Geomechanics and Geoengineering
• Subjects: Accretionary Prism; Clay Particle; Rigid Body Rotation; Rock Laboratory; Shear Zone
• ISBN: 331952772X; 9783319527727
• ISSN: 1866-8755; 1866-8763
• DOI: 10.1007/978-3-319-52773-4_40

Using a combined approach of ion-beam milling and electron microscopy, we observe, describe and quantify the microstructure of naturally and synthetically deformed Opalinus Clay (OPA) and deduce its microstructural evolution and underlying deformation mechanisms. The investigated samples derive from the so-called Main Fault, a 10 m offset fold-bend thrust fault crossing the Mont Terri Rock Laboratory in the Swiss Jura Mountains. The samples are slightly overconsolidated, experienced a burial depth of 1350 m and a maximum temperature of 55 °C. Most impact on strain is attributed to frictional sliding and rigid body rotation. However, trans-granular fracturing, dissolution-precipitation of calcite, clay particle neoformation and grain deformation by intracrystalline plasticity have a significant contribution to the fabric evolution. The long-term in-situ deformation behavior of OPA is inferred to be more viscous than measured at laboratory conditions.