How plate tectonic surface motions relate to the convecting mantle remains one of the major problems in geosciences. In particular, the cause and consequence of strain localization at plate boundaries remains debated, even though strain memory, i.e. the ability to preserve and reactivate tectonic inheritance over geological time, appears to be a critical feature in plate tectonics. Here, we analyze how a parameterized damage weakening rheology, strain-dependent weakening, affects the time-dependence of plate boundary formation, the transition between mobile and stagnant-lid, and the reorganization of plates in 2-D convection models. The strain-dependent weakening within our models allows for a self-consistent formation and preservation of lithospheric weak zones, which are formed as remnants of subduction zones due to large-scale compressional deformation in the trench region. Such inherited weak zones can be reactivated as intra-plate subduction zones, ridge adjacent subduction, or as spreading centers themselves. Due to the weakening along plate boundaries, the inherited weak zones, and partly the accumulated strain along spreading centers, which weakens the shallow parts of the lithosphere, the longevity of mobile-lid convection increases. Strain-dependent weakening also enhances strain localization along convergent plate boundaries which increases their stability and longevity. As a consequence, tectonic inheritance is an important contribution to understanding the time-dependence of plate reorganization. Strain-dependent weakening results in a shift of the mobile-stagnant lid transition to higher effective yield stresses, if the weak zones fully penetrate the lithosphere and are relatively weakened by at least 20 %.
S U M M A R YFormation of salt diapirs has been described to be due to upbuilding (i.e. Rayleigh-Taylor like instability of salt diapirs piercing through a denser sedimentary overburden) or syndepositional down-building process (i.e. the top of the salt diapir remains at the surface all the time). Here we systematically analyse this second end-member mechanism by numerical modelling. Four parameters are varied: sedimentation rate v sed , salt viscosity η salt , amplitude δ of the initial perturbation of the sedimentation layer and the wavenumber k of this perturbation. The shape of the resulting salt diapirs strongly depends on these parameters. Small diapirs with subvertical side walls are found for small values of v sed and η salt or large values of δ, whereas taller diapirs with pronounced narrow stems build for larges values of v sed and η salt or small values of δ. Two domains are identified in the four-parameter space, which separates successful down-building models from non-successful models. By applying a simple channel flow law, the domain boundary can be described by the non-dimensional law v sedcrit = C 1 1 2 δ 0 ρ sed k 2 k 2 +C 2 , where ρ sed is the sediment density scaled by the density contrast ρ between sediment and salt, the wavelength is scaled by the salt layer thickness h salt , and velocity is scaled by η salt /(h 2 salt ρg), where η salt is the salt viscosity and g is the gravitational acceleration. From the numerical models, the constants C 1 and C 2 are determined as 0.0283 and 0.1171, respectively.
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.
• 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
• 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
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