Understanding the temporal variability of Earth’s tectonics is key to
unraveling how mantle convection transports heat. The stability of plate
motions depends on rheological “memory”, i.e., the persistence of weak
zones. Here, we analyze the impact of such memory in global,
oceanic-lithosphere only models of visco-plastic mantle convection.
Self-consistently formed weak zones are reactivated in distinct modes,
and convection selects pre-damaged zones preferentially for new plate
boundaries. Any local stabilizing effects of weakening are overwhelmed
statistically by the accumulation of rheological heterogeneity.
Reactivation of damage zones increases the frequency of plate
reorganizations and thus reduces the dominant period of heat loss
fluctuations. In nature, the generation of sutures may thus counteract
and possibly overcome the effects of reduced convective vigor throughout
planetary cooling, with implications for the frequency of orogeny and
convective transport throughout Wilson cycles.