Global mantle convection models produce transform offsets along divergent plate boundaries

The presence of offsets, appearing at intervals ranging from 10s to 100s of kilometres, is a distinct characteristic of constructive tectonic plate margins. By comparison, boundaries associated with subduction exhibit uninterrupted continuity. Here, we present global mantle convection calculations that result in a mobile lithosphere featuring dynamically derived plate boundaries exhibiting a contrasting superficial structure which distinguishes convergence and divergence. Implementing a yield-stress that governs the viscosity in the lithosphere, spreading boundaries at the top of a vigorously convecting mantle form as divergent linear segments regularly offset by similar length zones that correlate with a large degree of shear but comparatively minimal divergence. Analogous offset segments do not emerge in the boundaries associated with surface convergence. Comparing the similarity in the morphologies of the model plate margins to the Earth's plate boundaries demonstrates that transform-like offsets are a result of stress induced weakness in the lithosphere owing to passive rupturing. In dynamic 3D spherical shell models, weakening due to convection induced stresses results in transform-like offsets which replicate the geometry of oceanic transform faults and have no clear dependence on the location of active upwellings

Automated summary

This study suggests that mantle convection can lead to the movement of lithosphere, resulting in dynamically derived plate boundaries with contrasting superficial structure that can distinguish between convergence and divergence.