Presentation by Nick Roberts.
'Coaxial Narrowing' in shear zones: a mechanism for transient behavior throughout the lithosphere?
Shear zones evolve dynamically throughout their evolution due to a variety of mechanisms, including rheological transformation, interaction with fluids, and changes in conditions. This talk considers the effect of deformation geometry on the dynamic state of shear zones through time. For a fixed imposed velocity, simple shear zones stay the same width through time and thus are steady state unless rheology or conditions change. Shear zones with a coaxial component (non-simple shear) may narrow through time purely as a result of the coaxial component. An analytical model shows how this type of 'coaxial narrowing' may drive large increases in differential stress over short (decade to millennium) scale time periods. The effect is particularly pronounced in highly localized shear zones in parts of the crust with high rheological contrast. This analytical model and examples throughout the lithosphere will be the basis for discussion on how non-simple shear deformation may drive transient behavior throughout the lithosphere when acting in concert with localizing mechanisms.
