Craig O’Neill, Adrian Lenardic, Matthew Weller, Louis Moresi, Steve Quenette, Siqi Zhang

Abstract: The tectonic regime of a planet depends critically on the contributions of basal and internal heating to the
planetary mantle, and how these evolve through time. We use viscoplastic mantle convection simulations, with evolving core–mantle boundary temperatures, and radiogenic heat decay, to explore how these factors affect tectonic regime over the lifetime of a planet. The simulations demonstrate (i) hot, mantle conditions, coming out of a magma ocean phase of evolution, can produce a ‘‘hot” stagnant-lid regime, whilst a cooler post magma ocean mantle may begin in a plate tectonic regime; (ii) planets may evolve from an initial hot stagnant-lid condition, through an episodic regime lasting 1–3 Gyr, into a plate-tectonic regime, and finally into a cold, senescent stagnant lid regime after
10 Gyr of evolution, as heat production and basal temperatures wane; and (iii) the thermal state of the post magma ocean mantle, which effectively sets the initial conditions for the sub-solidus mantle convection phase of planetary evolution, is one of the most sensitive parameters affecting planetary evolution – systems with exactly the same physical parameters may exhibit completely different tectonics depending on the initial state employed. Estimates of the early Earth’s temperatures suggest Earth may have begun in a hot stagnant lid mode, evolving into an episodic regime throughout most of the Archaean, before finally passing into a plate tectonic regime. The implication of these results is that, for many cases, plate tectonics may be a phase in planetary evolution between hot and cold stagnant states, rather than an end-member.

O’Neill, C., A. Lenardic, M. Weller, L. Moresi, and S. Quenette, A window for plate tectonics in terrestrial planet evolution, Phys. Planet. Int., 255, 80-92, 2016.