The interaction of viscous heating with grain‐size dependent rheology in the formation of localized slip zones

Abstract

Abstract.The formation of localized shear zones is important for understanding many local and global processes in geodynamics. We have developed a selfconsistent thermal-mechanical model together with a rheology which depends on temperature, strain-rate and grain-size distribution. The grain-size distribution has contributions from both dynamic recrystallization and grain-growth processes, and is governed locally We will focus especially on the delicate interplay between the fault-narrowing tendency from viscous heating and the fault-healing influence from grain-growth in controlling the fate of these localized shear zones, with dimensions on the order of hundreds of meters.

Grain-size-sensitive flow and shear-stress enhancement at the brittle–ductile transition of the continental crust

“…The key issue is the definition of the steady-state grain size, also called the mean grain size in the literature, which acts as an attractor during transient evolutions. This steady-state value is not the value deduced from piezometric measurements and adopted by Kameyama et al (1997) and Braun et al (1999). In that case, the recrystallized grain size±stress relationship is independent of the boundary between dislocation creep and diffusion creep domains in a deformation map (Derby and Ashby 1987;Shimizu 1998).…”

“…Note that the evolution ceases if either the steady state is reached ( d D) or the deformation mechanism is not activated. Other evolution laws for grain size are found in the literature, especially for olivine (Derby and Ashby 1987;Kameyama et al 1997;Braun et al 1999). Equation (9) is simpler than the ones referred above in the sense that it combines the evolution law for grain-size reduction and grain growth in a single expression.…”

“…Hopper and Buck (1993) documented the role of diffusion creep (grain-size sensitive rheology) in the upper mantle in the initiation of rifting. The competing effects between grain growth, which inhibits the development of shear zones in the mantle, and grain-size reduction, associated with viscous heating and dynamic recrystallization, were illustrated in a 1-D numerical analysis by Kameyama et al (1997) and also by Braun et al (1999).…”

Grain size reduction by dynamic recrystallization: can it result in major rheological weakening?

“…The above implies that, at constant temperature, grain size reduction by dynamic recrystallization is not expected to result in a major change in strength or effective viscosity of a material deforming in steady state. These findings will influence numerical modeling performed to determine the conditions under which strain localization takes place (e.g., Kameyama et al 1997;Braun et al 1999). These conditions play an important role in large-scale models of lithosphere deformation and mantle flow.…”

Dependence of diffusive radiative transfer on grain-size, temperature, and Fe-content: Implications for mantle processes

“…This dependence leads to a non-linear response to strain and heating (Kameyama et al, 1997;Braun et al, 1999), and, thus, viscosity is considered to be important in earth's thermal history (e.g. Tozer, 1965;Stacey and Loper, 1988).…”