Deformation Memory in the Lithosphere: A Comparison of Damage‐dependent Weakening and Grain‐Size Sensitive Rheologies

Abstract

• Comparative analysis of strain localization and damage memory for grain-size dependent and strain/ damage parameterized rheologies • Identification of key ingredients of strain localization and damage hysteresis and how to represent those in planetary-scale modeling • Plastic strain softening enables hysteresis with a memory duration similar to grain growth at lithospheric temperature conditions

On the Role of Rheological Memory for Convection‐Driven Plate Reorganizations

“…Here, we assume that a linear reduction of the yield stress due to γ, that is, plastic-strain softening, results in rheological weakening. Plastic-strain softening best approximates the transient weakening and hardening behavior of a GSS, composite rheology (Fuchs & Becker, 2021). While we limit the rheological weakening and hardening rates to the transient behavior of GSS rheology, additional microphysical mechanisms might be used as further constraints.…”

“…Foley and Bercovici, 2014). As discussed by Fuchs and Becker (2021), we choose values for B and η γ which result in similar (and slower) hardening rates compared to a single mineral phase, composite, grain-size-sensitive (GSS) rheology (cf. Hirth & Kohlstedt, 2003;Behn et al, 2009;Foley and Bercovici, 2014; see Text S2 in Supporting Information S1 for more details).…”

“…Simplified descriptions based on tracking an evolving damage variable can capture much of the more complex hysteresis due to grain-size dependence (Fuchs & Becker, 2021), and such approximations are more readily explored within convection models (e.g., Ogawa, 2003;Tackley, 2000a). Here, we build on a range of earlier 2-D modeling and explore, to our knowledge for the first time, the effects of memory on global, visco-plastic convection.…”

Plume‐Slab Interactions Can Shut Off Subduction

“…We consider a strain-based damage variable, γ, which is treated as a field variable, that is, a compositional field that is advected and can evolve. The combination of plasticity and evolving, damage-type rheology can approximate more realistic weakening processes such as inferred from grain-size-dependent rheologies (Fuchs & Becker, 2021). Damage evolves according to a discretized evolution law…”

“…For a given temperature-dependent viscosity, the vigor of convection is tied to the convective regime of the model, and without plastic yielding, stagnant lid convection results in contrasts above ∼1,000 (Solomatov & Moresi, 1997). With damage rheology choices similar to Fuchs and Becker (2019); Fuchs and Becker (2021) for the strain-weakening and strain-healing, we adjust our models to be on the edge between episodic and mobile regimes. In particular, we show results from two models which yielded an episodic case (Model 1, yield stress 65 MPa) and a more mobile case (Model 2, yield stress 60 MPa) both with a Rayleigh number of ∼2.3 ⋅ 10 7 .…”