A THINNED LITHOSPHERE UNDER THE REUNION H OT-SPOT - CLUES FROM A NEW SET OF HEAT-FLOW DATA ACQUIRED OVER THE MASCARENE RIDGE

New heat flow data have been collected along two profiles perpendicula r to the Mascarene ridge, Indian Ocean, by the French RV Marion-Dufres ne (Mascaflux 92 cruise). The volcanic relief of the aseismic ridge is due to an asthenospheric mantle plume, now responsible for the active volcanism of Reunion Island. After being corrected for the effects of sedimentation, the heat flow data exhibit short (<100 km) and middle wavelength variations (= 400 km). The former can be associated with th e effects of basement relief as well as seafloor topographic effects. The latter are clearly linked to the ridge. The entire high quality da ta set has a mean value 8 to 10 mW.m(-2) higher than the theoretical v alue deduced from the cooling of the lithosphere with age. This could be related to the generally elevated basement topography (mean anomalo us height similar to 800 m) extending largely beyond the limits of the profiles. This topographic high is also associated to a -40 mgal free air gravity anomaly. A model of mantle plume-lithosphere interaction where both the lithosphere is thinned, and a dynamical uplift exists f rom below, is suggested to explain all the geophysical observations.