A mantle convection perspective on global tectonics
The concept of interplay between mantle convection and tectonics goes back to about a century ago, with the proposal that convection currents in the Earth's mantle drive continental drift and deformation (Holmes, 1931) Since this time, plate tectonic theory has established itself as the fundamental framework to study surface deformation, with the remarkable ability to encompass geological and geophysical observations. Mantle convection modeling has progressed to the point where connections with plate tectonics can be made, pushing the idea that tectonics is a surface expression of the global dynamics of one single system: the mantle lithosphere system. Here, we present our perspective, as modelers, on the dynamics behind global tectonics with a focus on the importance of self organisation. We first present an overview of the links between mantle convection and tectonics at the present day, examining observations such as kinematics, stress and deformation. Despite the numerous achievements of geodynamic studies, this section sheds light on the lack of self organisation of the models used, which precludes investigations of the feedbacks and evolution of the mantle lithosphere system. Therefore, we review the modeling strategies, often focused on rheology, that aim at taking into account self organisation. The fundamental objective is that plate like behaviour emerges self consistently in convection models. We then proceed with the presentation of studies of continental drift, seafloor spreading and plate tectonics in convection models allowing for feedbacks between surface tectonics and mantle dynamics. We discuss the approximation of the rheology of the lithosphere used in these models (pseudo plastic rheology) for which empirical parameters differ from those obtained in experiments. In this section, we analyse in detail a state of the art 3 D spherical convection calculation, which exhibits fundamental tectonic features (continental drift, one sided subduction, trench and ridge evolution, transform shear zones, small scale convection, and plume tectonics) This example leads to a discussion where we try to answer the following question: can mantle convection models transcend the limitations of plate tectonic theory?