The investigation of the progressive microstructural development and related deformation mechanisms in shear zones is important for our understanding on strain localization, lithospheric strength, and geodynamic processes in general. Microstructures and textures represent the link between natural and experimental rock deformation, allowing for an application and extrapolation of laboratory data to natural shear zones and rock rheology. Changes in mechanical behaviour and rock strength are usually documented by the deformation microstructure. These changes can be due to transitions in deformation mechanisms (controlled by temperature and strain rate), fluid-rock-interaction and metamorphic reactions, and result either in deformation softening or hardening potentially leading to strain localization vs. spreading. Metamorphic reactions allow for the determination of PT conditions and for an estimate on the presence or absence of water. However, connecting the microstructural and textural data to metamorphic conditions and timing of deformation remains mostly qualitative. Likewise, linking the absolute timing of deformational events or stages to PT paths is commonly hampered by: 1) difficulty in correlating thermobarometric and chronologic data from the same rock sample, 2) relatively large uncertainties associated with conventional thermobarometry, 3) lack of suitable metamorphic mineral assemblages in mylonites. Recently developed Ti-in-quartz thermometer (TitaniQ) may offer a quantitative estimate of deformation temperatures in quartz mylonites. Combining metamorphic petrology, trace element geothermometry, thermodynamic modelling, and microstructural geology is therefore essential for our understanding of the formation and maintenance of shear zones in the lithosphere.
This session presents case and generic studies of rock deformation under range of metamorphic conditions in nature, experiment and theory. It aims at spanning a bridge from micromechanics to multi-scale field-based investigations and to lithosphere rheology. Three oral sessions will discuss topics on (a) Strain localization and rheology, (b) Taking temperature of ductile deformation, and (c) Deformation mechanisms.
Martyn Drury, Utrecht University (Utrecht, Netherlands)
Laurent Jolivet, Orleans University (Orleans, France)
Holger Stunitz, University of Tromsø (Tromsø, Norway)
Jay Thomas, Rensselaer Polytechnic Institute (Troy, NY United States)