The lithosphere is the barrier and connector between the deep interior of a rocky planet and its surface environment. On Earth, plate tectonics is responsible for recycling the lithosphere back into the mantle and for significantly driving volcanism and planetary cooling. However, other planets like Mars or Venus show no signs of plate tectonics. How does plate tectonics operate? How did it evolve on the Earth and on what kind of planets in the Galaxy can we expect plate tectonics? I use thermodynamics to understand the evolution of plate tectonics with a focus on the early Earth, the terrestrial water cycle, and on understanding how (and why) the tectonic modes of Venus, Mars and rocky exoplanets might differ from the Earth.


Tectonics

connecting interiors to our surface world

All Right Reserved, 2016 Vlada Stamenkovic.

  1. Bullet HIGHLIGHTS

  2. BulletBottom-up approach for the drivers of plate tectonics revising our common “beliefs” about plate failure and subduction and the thermal evolution of rocky planets: showing that temporal variation of basal shear stresses and asthenospheric channels drive the initiation of plate tectonics, and that classic self-determined boundary layer analysis cannot be used to model the evolution of the Earth. In more detail, we use 1-D thermal history models and 3-D numerical experiments to study the impact of dynamic thermal disequilibrium and large temporal variations of normal and shear stresses on the initiation of plate tectonics. Previous models that explored plate tectonics initiation from a steady state, single plate mode of convection concluded that normal stresses govern the initiation of plate tectonics, which based on our 1-D model leads to plate yielding being more likely with increasing interior heat and planet mass for a depth-dependent Byerlee yield stress. Using 3-D spherical shell mantle convection models in an episodic regime allows us to explore larger temporal stress variations than can be addressed by considering plate failure from a steady state stagnant lid configuration. The episodic models show that an increase in convective mantle shear stress at the lithospheric base initiates plate failure, which leads with our 1-D model to plate yielding being less likely with increasing interior heat and planet mass. In this out-of-equilibrium and strongly time-dependent stress scenario, the onset of lithospheric overturn events cannot be explained by boundary layer thickening and normal stresses alone. Our results indicate that in order to understand the initiation of plate tectonics, one should consider the temporal variation of stresses and dynamic disequilibrium.

  3. BulletThe connections between plate tectonics, planet composition, structure, and initial conditions: Showing how the initiation and maintenance of plate tectonics depend on planet composition (i.e., concentration of radioactive elements, iron, and carbon), initial conditions, and core and planet size. With crucial implications for Earth, Mars, and exoplanets. In more detail, to understand the evolution and the habitability of any rocky exoplanet demands detailed knowledge about its geophysical state and history— such as predicting the tectonic mode of a planet. Yet no astronomical observation can directly confirm or rule out the occurrence of plate tectonics on a given exoplanet. Moreover, the field of plate tectonics is still young— questioning whether we should study plate tectonics on exoplanets at this point in time. In this work, we determine the limitations and the emerging possibilities of exogeophysics, the science of connecting geophysics to exoplanets, on the example of plate tectonics. Assuming current uncertainties in model and planet parameters, we develop a qualitatively probabilistic and conservative framework to estimate on what kind of planets and where in the Galaxy plate tectonics might occur. This we achieve by modeling how plate yielding, the most critical condition needed for plate mobility and subduction, is affected by directly observable (planet mass, size)  or indirectly, to some degree, assessable planet properties ( structure and composition). Our framework not only highlights the importance of a planet’ s chemistry for the existence of plate tectonics and the path toward practical exogeophysics but also demonstrates how exoplanet science can actually help to better understand geophysics and the fundamentals of plate tectonics on Earth itself.































  1. Bullet FURTHER READING

  2. BulletStamenković, V., Höink, T., Lenardic, T., 2016. The importance of temporal stress variation for the initiation of plate tectonics. JGR Planets, 121, 1–20, doi:10.1002/2016JE004994.

  3. BulletStamenković, V., Seager, S., 2016. Emerging possibilities and insuperable limitations of exogeodynamics: the example of plate tectonics. The Astrophysical Journal, 825, 78-95.

  4. BulletStamenković, V., Breuer, D., 2014. The tectonic mode of rocky planets, Part 1: driving factors, models & parameters. Icarus 234, 174-193.