Abstract
Phase transformations greatly affect physical properties of rocks and impose a first-order control on geodynamic processes. Under high deformation rates, rheological heterogeneities cause large spatial variations of stress in materials. Until now, the impact of higher deformation rates, rock heterogeneity and stress build up on phase transformations and material properties is not well understood. Here we show, that phase transitions are controlled by the stress build-up during fast deformation. In a deformation experiment (600 °C, 1.47 GPa), rock heterogeneity was simulated by a strong elliptical alumina inclusion in a weak calcite matrix. Under deformation rates comparable to slow earthquakes, calcite transformed locally to aragonite matching the distribution of maximum principal stresses and pressure (mean stress) from mechanical models. This first systematic investigation documents that phase transformations occur in a dynamic system during deformation. The ability of rocks to react during fast deformation rates may have serious consequences on rock rheology and thus provide unique information on the processes leading to giant ruptures in subduction zones.
Highlights
Phase transformations greatly affect physical properties of rocks and impose a first-order control on geodynamic processes
Phase transformations have a great influence on rheology through variations in mineral assemblages, mechanical properties, the presence of fluid or a change in grain size[1,2]
Understanding processes during fast deformation events depends on identifying material behavior and its rheology
Summary
Phase transformations greatly affect physical properties of rocks and impose a first-order control on geodynamic processes. As recently documented by geophysical methods, transient periods with higher deformation rates (10−9–10−10s−1) and stress build-up are more frequent than previously thought[6,7] These fast deformation events can result in large earthquakes with direct societal consequences. The effect of elliptical heterogeneities on the stress field of a deforming viscous material has been investigated by analytical solutions[4,17] These models show that material heterogeneity, expressed as viscosity heterogeneity, can lead to the development of stress and pressure spatial variations around a strong inclusion (Fig. 1). Such models do not involve reacting materials and they do not consider the interplay between phase transformations and deformation
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