The Earth continuously releases its heat via convective motion in the Earth's mantle, which underlies the crust. Understanding this convection is therefore fundamental to the study of plate tectonics. The mantle is made up of solid rocks. In order for convective motion to occur, it must be possible for the crystal lattice of these rocks to deform. Until now, this was a paradox that science was unable to fully resolve. While defects in the crystal lattice, called dislocations, provide a very good explanation of the plasticity of metals, they are insufficient to explain the deformations undergone by certain mantle rocks.
The researchers suspected that the solution was to be found at the boundaries between the mineral grains that make up rocks. However, they lacked the conceptual tools needed to describe and model the role played by these boundaries in the plasticity of rocks. Researchers at the Unité Matériaux et Transformations (CNRS/Université Lille 1/Ecole Nationale Supérieure de Chimie de Lille) in collaboration with researchers at the Laboratoire Géosciences Montpellier (CNRS/Université Montpellier 2) and the Laboratoire d'Etude des Microstructures et de Mécanique des Matériaux (CNRS/Université de Lorraine/Arts et Métiers ParisTech/Ecole Nationale d'Ingénieurs de Metz) have now explained this role.
This research goes beyond explaining the plasticity of rocks in the Earth's mantle: it is a major step forward in materials science. Consideration of disclinations should provide scientists with a new tool to explain many phenomena related to the mechanics of solids. The scientists intend to continue their research into the structure of grain boundaries, not only in other minerals but also in other solids such as metals.