Numerical modeling of viscoplastic mantle convection with damage rheology to investigate dynamics of plate tectonics




Heilman, Erin

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Mantle plumes are typically considered secondary features of mantle convection, yet their surface effects over Earth's evolution may have been significant. We use 2-D convection models to show that mantle plumes can in fact cause the termination of a subduction zone. This extreme case of plume-slab interaction is found when the slab is readily weakened, e.g. by damage-type rheology, and the subducting slab is young. We posit that this mechanism may be relevant particularly for the early Earth, and more generally, plume "talk back" to subduction zones may make plate tectonics more episodic in certain cases. When these models are carried out in a 3-D geometry, we see the same plume-slab terminations take place and can observe the effect of lateral extent on the dynamics. We examine the dynamics of these terminations through their geometry, frequency, and effect on the surface. By varying the proportion of internal heating, we show the effect of mantle temperature on the efficacy of plume-slab terminations and draw parallels to the evolution of the Earth's mantle temperature. A subdued version of these plume-slab interactions may remain relevant for past and modern subduction zones. Such core-mantle boundary – surface interactions may be behind some of the complexity of tomographically imaged mantle structure, e.g., for South America. Continuing the exploration of our damage rheology, we investigate spreading ridges, which are another feature integral to plate tectonics. We carry out 3-D internally heated mantle convection modeling to produce discrete spreading ridges and transform faults in a freely convecting model. The inclusion of damage in these models allows for transform faults to develop more easily than in previous modeling attempts. We vary the strength of the damage in its weakening and healing proportions to understand the effect on the dynamics and lifespan of the transform faults. These transform faults match well with observations from Earth, and as a result these models are a stepping stone to a new class of global mantle convection modeling.


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