Evolving Lid-States, Bi-Stability, and the Evolution of Terrestrial Planets

English Abstract:

We use 3D mantle convection and planetary tectonics simulations to explore the links between tectonic regimes, lithospheric yield strength, the age of a planet, and thermal histories. At both high and low values of internal heating a single hot or cold stagnant-lid end state prevails. For lower initial and/or depleted radiogenics (e.g. thermal ageing) hot stagnant-lid states can yield through an episodic-lid, into a mobile-lid regime. Further reducing radiogenics leads the mobile-lid transitioning back into a (now) cold stagnant-lid. While high and low temperature tectonic end states may be fixed, the intermediate parameter range – a significant span of a planet’s thermal evolution – may be governed by the thermal history of the system (e.g. initial conditions) allowing for regions of multiple stable tectonic states, or bi-stability. Within the bi-stability window, the tectonic regime becomes a function of a planet's specific geologic and climatic history. The timing of transitions in tectonic regimes is linked to internal temperature variations, which are a function of the lid-state evolution. Transitions from an initial stagnant-lid state are delayed (requiring a larger decrease in radiogenics) as a function of increasing yield strength and surface temperature, indicating that a system with a different thermal evolution has the potential to migrate through tectonic regimes at the same ‘thermal time’ (e.g. temperature), but very different ‘temporal times’. Our results indicate that multiple modes of convection and surface tectonics can potentially operate on a single planetary body at different times in its evolution, as consequence of changing internal parameters, surface temperatures, and differing thermal histories, implying terrestrial worlds can alternate, and be offest between multiple tectonic states over giga-year timescales.