Continental Hotspots Tracks from Analysis of GOCE Gravity Gradients Data

 Hotspots are thermal instabilities that originate in the mantle and manifest themselves on the surface by volcanism, continental breaks or "traces" observed in the oceans. Theirs effects under the continents are still debated: in addition to a phase of activity associated with surface volcanism, a residual thermal anomaly could persist durably under the lithosphere along the trajectory of the hotspot. For a simple model of thermal anomaly (a parallelogram aligned in a fixed direction), we compute the perturbations of the geoid, of the gravity vector and of the associated gravity gradients, and show that in a coordinate system aligned with the parallelogram, the gravity gradients exhibit a characteristic signal, with an order of magnitude of a few hundred mEotvös, well above the current data detection level. Thus considering four real cases :in North Africa (with Hoggar, Tibesti, Darfur and Cameroon hotspots), in Greenland (Iceland), in Australia (Cosgrove) and in Europe (Eifel), we calculate the paleo-positions of the hotspots for 100 Myr in a reference frame linked to the lithospheric plates, and we build maps of the Bouguer gravity gradients filtered on the spatial scale of a few hundred kilometers (the scale of the hotspot) and oriented along the direction of these trajectories. We clearly detect, in the scale-orientation diagrams, signals aligned in the direction of the movement of the plates on spatial scales of a few hundred kilometers. These preliminary results are very enthusiastic: gradiometric data indeed allow us to follow the tracks of hotspots in the continental lithosphere, for at least 20 Myr.