Plate tectonics introduces chemical, thermal, viscosity, melting and density inhomogeneities into the mantle, and stress inhomogeneity into the plates. Idealized models often assume uniform mantle and rigid, homogeneous plates, and require separate, ad hoc explanations for island chains, melting anomalies and continental breakup. Plates, however, drive and break themselves and organize the underlying mantle, in common with other cooled-from-above systems.

Plate tectonics introduces chemical, thermal, viscosity, melting and density inhomogeneities into the mantle, and stress inhomogeneity into the plates. Idealized models often assume uniform mantle and rigid, homogeneous plates, and require separate, ad hoc explanations for island chains, melting anomalies and continental breakup. Plates, however, drive and break themselves and organize the underlying mantle, in common with other cooled-from-above systems.

Pressure, often ignored or approximated in simulations, suppresses thermal expansion and the Rayleigh number. This makes the deep mantle a sluggish system with gigantic features, consistent with tomography, and isolated from the upper mantle and plate tectonics except by conduction and gravity. Chemical stratification is thus likely.

Plate tectonics, with adjectives such as rigid, homogeneous, isothermal, fixed, subsolidus, reservoir, steady-state etc. dropped, is a much more powerful concept than generally believed. Cracks, rif ...more