CHARACTERIZATION OF SECONDARY MANTLE CONVECTION FROM GEOPHYSICAL DATA AND MODELS

Mantle convection occurs at different scales. Large-scale convection occurs at the scale of lithospheric plates. Small scale convection, or secondary convection, occurs at a smaller scale, generally as sub-lithospheric longitudinal rolls, induced by the shear associated with the lithospheric plates motion. Most of the heat out of the Earth’s mantle is transported by the large-scale convection, but secondary convection is required in order to account for the observed heat dissipation near the surface. Secondary convection not only provides the complete picture of the heat transfer from the mantle to the surface, but also defines the coupling between mantle and lithosphere. The first insights on secondary convection come from geoid and gravity data in the Pacific and Indian oceans. Since then, there have been several studies trying to assess the phenomenology of the small-scale convection, mainly through numerical or experimental studies. However, applying the results of such studies to what is actually happening in the Earth’s mantle is not straightforward. Geophysical data would be the best tool to describe the characteristics/morphology of the secondary convection, and therefore help constraining the origin and dynamics of this convective pattern. In this study, we infer the destabilization of the oceanic lithosphere from global tomography models, and discuss how it is related to secondary convection.