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

Abstract

Understanding the temporal variability of plate tectonics is key to unraveling how mantle convection transports heat, and one critical factor for the formation and evolution of plate boundaries is rheological “memory,” that is, the persistence of weak zones. Here, we analyze the impact of such damage memory in global, oceanic‐lithosphere‐only models of visco‐plastic mantle convection. Self‐consistently‐formed weak zones are found to be reactivated in distinct ways, and convection preferentially selects such damaged zones for new plate boundaries. Reactivation of damage zones increases the frequency of plate reorganizations, and hence reduces the dominant periods of surface heat loss. The inheritance of distributed lithospheric damage thus dominates global surface dynamics over any local boundary stabilizing effects of weakening. In nature, progressive generation of weak zones may thus counteract and perhaps overcome any effects of reduced convective vigor throughout planetary cooling, with implications for the frequency of orogeny and convective transport throughout Wilson cycles.

Generation of Evolving Plate Boundaries and Toroidal Flow From Visco‐Plastic Damage‐Rheology Mantle Convection and Continents

“…Given our choices of rheological parameters, this range of variation is slightly less than in the purely visco‐plastic computations of Langemeyer et al. (2021), for example, which is partially because of damage and corresponding sutures (Fuchs & Becker, 2022). There are also some broad, intraplate deformation zones that are ∼1,000 lower in viscosity than the interior of the plates.…”

“…This highlights a major issue, trying to distinguish the effects of damage leading to locally reduced yield stress, as opposed to globally modified yield stress (cf. Fuchs & Becker, 2022). We are currently conducting regional computations to further explore these issues, but from our preliminary assessment, it appears that damage rheology is one way to produce Earth‐like tectonic complexity such as in Figure 9 while remaining in a mobile rather than episodic state, at least for oceanic lithosphere‐only models.…”

“…To solve these equations, we use the finite element code CitcomS (Moresi & Solomatov, 1995; Zhong et al., 2000) with the tracer implementation of McNamara and Zhong (2004) which is used to track the nominally diffusion‐free and source‐less C field according to $$$\frac{\partial C}{\partial t}+\left(\boldsymbol{u}\cdot \nabla \right)C=0,$$$ where C denotes continental material with different strength and buoyancy (see below). Our general setup closely follows Fuchs and Becker (2022); we consider purely internally heated convection and use visco‐plastic rheologies with damage to explore plate‐like planforms of convection.…”

“…Unlike most previous, global plate‐generating convection modeling, with the exception of Fuchs and Becker (2022), we also explore the role of damage rheology for the planform of convection. For this, we use a simplified description that tracks a damage variable d using tracers and integrating over $${\dot{{\epsilon}}}_{\text{II}}$$ and allowing for healing (Ogawa, 2003; Tackley, 2000a) $$$\frac{\mathrm{d}d}{\mathrm{d}t}={\dot{{\epsilon}}}_{\text{II}}-d\ \mathrm{exp}\left(-\left(\frac{{E}_{d}}{T+1}-\frac{{E}_{d}}{2}\right)\right)B,$$$ where B is the healing rate, and E d quantifies the temperature‐dependence of healing akin to Equation , for simplicity.…”

“…For H = 120, when expressing Ra in terms of mantle thickness, Ra D , the internal heating Rayleigh number is thus Ra D H ∼ 1.1 ⋅ 10 9 , and when further adjusted for a typical depth‐average of viscosity 〈 η 0 〉 ∼ 100 (Figure A1), the effective Rayleigh number is ∼10 7 . Parameters are otherwise as in Fuchs and Becker (2022).…”