- © The Mineralogical Society Of America
It is widely recognized that Earth sciences were revolutionized when continental drift proposed by Wegener in 1912 took the more comprehensive form of plate tectonics. Following the early suggestion of Holmes, Hess proposed in the early sixties what missed to Wegener’s model: a mechanism and a driving force, i.e., the presence of large flows within the convecting mantle to evacuate the internal heat. The Earth appears now as a dynamic system dominated by flows and deformation processes almost everywhere: convective flow in the liquid core (which is the source of the Earth magnetic field), slow deformation of the hot (viscous?) solid mantle and rigid brittle deformations of the cold crust. Understanding and modeling the deformation mechanisms of Earth materials is thus one of the most important challenges of geophysics. Among the three large topics listed above, we will focus on mantle convection only. Two scientific fields which developed approximately at the same time (i.e., just before and just after the second world war) meet here: geophysics and materials science which aims at explaining how solids can deform (see below). Mantle convection raises however some questions that are specific to this field:
Which minerals are involved and what are their deformation mechanisms?
What is the influence of pressure on plastic deformation?
What is the influence of extremely low strain rates on deformation mechanisms?
Although some very significant advances have been achieved recently on the experimental side (see for instance Karato and Weidner 2008) most of these questions remain largely unsolved and at the limits of our capabilities. It appears thus necessary to complement the usual experimentally-based approach by a numerical, multi-scale modeling approach in order to increase the significance of our models. This multi-scale modeling must be based on the Physics at the relevant scales (see Fig. 1⇓) and will …