Mantle convection with strong plates and the tectonic mode of a terrestrial planet
Abstract
Cool and dense oceanic plates descend into the hot mantle at subduction zones and provide one of the largest sources of (negative) buoyancy and potential energy that drives the motion of the convecting system. This energy is used to deform and subduct the plate (necessary for plate tectonics) as well as to drive flow in the interior of the Earth (mantle convection). Sufficient energy must be provided to the plates to maintain Earth-like plate tectonics. Understanding what controls the partitioning of available energy between the plate and the mantle is fundamental to elucidating the dynamical state of the system. Both numerical and analytic models of coupled mantle convection and planetary tectonics are used to demonstrate that history dependence may play a more pivotal role in determining a planets tectonic state than previously thought. The mantle convection-surface tectonics system allows multiple tectonic modes to exist, each with distinct (dominant) plate driving and resisting forces, for the same planetary energy content and material parameters. The tectonic mode of a planet is then determined by its specific geologic and climatic history. This implies that models of tectonics and mantle convection may not be able to uniquely determine the tectonic mode of a terrestrial planet without the addition of historical data and emphasises the potential importance of the initial condition in determining a planets evolutionary path. Historical data exists, to variable degrees, for all four terrestrial planets within our solar system. For the Earth, the planet with the largest amount of observational data, debate does still remain regarding the geologic and climatic history of Earth's deep past but constraints are available. For planets in other solar systems, no such constraints exist at present. The existence of multiple tectonic modes, for equivalent parameter values, may help to explain why different groups have reached different conclusions regarding the tectonic state of extrasolar planets larger than Earth ("super-Earths"). The models demonstrate that the subspace allowing multiple stable solutions widens in parameter space for more energetic mantle convection, as would be expected for larger or hotter planets. This means that different groups can find different solutions, all potentially viable and stable, using identical models and identical system parameter values. As such, these results have important implications for unraveling the early thermal evolution of the Earth, where a warmer mantle would have likely permitted the existence of multiple stable tectonic modes.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.T33J..08C
- Keywords:
-
- 5475 PLANETARY SCIENCES: SOLID SURFACE PLANETS / Tectonics;
- 8120 TECTONOPHYSICS / Dynamics of lithosphere and mantle: general;
- 8125 TECTONOPHYSICS / Evolution of the Earth;
- 8177 TECTONOPHYSICS / Tectonics and climatic interactions