Plate tectonics on Earth: observations, driving forces and temporal evolution.
Laboratoire de Géologie de Lyon, Université Lyon 1,
Web Lecture on January 27, 2022 at 3:00 PM (Paris Time)
The present-day activity at the surface of our Planet is the result of heat transfer from its deep interior, and notably manifests as earthquakes, volcanism, surface lateral motions and surface topography. Since the 1930’s, these observations of the constantly changing face of our Planet have given rise to the theory of plate tectonics, which kinematically describes the lateral motion of rigid blocks – or plates – on a spherical surface, with deformations acting only at their boundaries. Although being now widely accepted and consistent with Earth’s surface geological record, this simple vision of the evolution of the Earth’s surface is still incomplete.
Indeed, the quality of current plate tectonic reconstructions is limited to recent geological times by the number of well-preserved rocks at the surface of our Planet. Therefore, reconstructions of past plate tectonic motions are highly unconstrained for times older than 200 Myr. A related important question concerns the start of the plate tectonics on Earth: has it started soon after the differentiation of our Planet or later? Was early plate tectonics similar in dynamics to what we observe today or completely different? How did the surface of our planet look like in these early times? Here again, the limited geological record of such ancient periods is a large obstacle to the reconstruction of the surface of our Planet for ages older than 1 Gyr.
Moreover, even on present-day Earth, some observations, such as the existence of diffuse deformation in the interior of plates, cannot be explained by the kinematic theory of plate tectonics, and require knowledge on the physical feedbacks between a convective mantle and a laterally-moving lithosphere. A geodynamical description of plate tectonics is therefore required in order to better constrain both present-day and past plate tectonics and its driving forces.
In this presentation, I will first present the theory of plate tectonics. Then, using a combination of a diversity of geological information and the results of numerical models of mantle convection self-generating plate-like behaviour (Fig. 1), I will show how multidisciplinary efforts among the Earth Science community are made to improve our understanding and reconstruction of our Planet’s past surface tectonics. I will present some of the most recent results obtained in these directions and I will discuss some of the challenges that we still face to fully embrace the long-term past evolution of our Planet’s surface.