Abstract
The initiation mechanism of Earth’s plate tectonic cooling system remains uncertain. A growing consensus suggests that multi-plate tectonics was preceded by cooling through a single-plate lithosphere, but models for how this lithosphere was first broken into plates have not converged on a mechanism or a typical early plate scale. A commonality among prior efforts is the use of continuum mechanics approximations to evaluate this solid mechanics problem. Here we use 3D spherical shell models to demonstrate a self-organized fracture mechanism analogous to thermal expansion-driven lithospheric uplift, in which globe-spanning rifting occurs as a consequence of horizontal extension. Resultant fracture spacing is a function of lithospheric thickness and rheology, wherein geometrically-regular, polygonal-shaped tessellation is an energetically favored solution because it minimizes total crack length. Therefore, warming of the early lithosphere itself—as anticipated by previous studies—should lead to failure, propagating fractures, and the conditions necessary for the onset of multi-plate tectonics.
Highlights
The initiation mechanism of Earth’s plate tectonic cooling system remains uncertain
We find that thermal expansion in response to anticipated warming of the early lithosphere[3] leads to fracture propagation and eventual coalescence of a global fracture network
Our spherical shell models show how a tectonic plate system can evolve from shallow processes
Summary
A growing consensus suggests that multi-plate tectonics was preceded by cooling through a single-plate lithosphere, but models for how this lithosphere was first broken into plates have not converged on a mechanism or a typical early plate scale. Warming of the early lithosphere itself—as anticipated by previous studies —should lead to failure, propagating fractures, and the conditions necessary for the onset of multi-plate tectonics. Most models envisage initial conditions of a stagnant lid (i.e., a single-plate lithosphere) atop a mantle which was hotter by a few hundred degrees than the present mantle It is appropriate, to bring to bear a new solid mechanics-based approach to the problem of the origin of plate tectonics and the processes by which plate boundaries are initiated. We use three-dimensional (3D) spherical shell models of a brittle lithosphere to explore the geodynamical processes that initiate tectonic boundaries. Fractures themselves could concentrate volcanism by providing distinctively easy routes to the surface, which in turn could weight the lithosphere locally and provide the initial impetus for subduction tectonics
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