GRAVITY AND MULTICHANNEL SEISMIC-REFLECTION CONSTRAINTS ON THE LITHOSPHERIC STRUCTURE OF THE CANARY-SWELL

Deep penetrating multichannel seismic reflection and gravity data have been used to study the lithospheric structure of the Canary Swell. Th e seismic reflection data show the transition from undisturbed Jurassi c oceanic crust, away from the Canary Islands, to an area of ocean cru st strongly modified by the Canary volcanism (ACV). Outside the ACV th e seismic records image a well layered sedimentary cover, underlined b y a bright reflection from the top of the igneous basement and also re latively continuous reflections from the base of the crust. In the ACV the definition of the boundary between sedimentary cover and igneous basement and the crust-mantle boundary remains very loose. Two-dimensi onal gravity modelling in the area outside the influence of the Canary volcanism, where the reflection data constrain the structure of the o cean crust, suggests a thinning of the lithosphere. The base of the li thosphere rises from 100 km, about 400 km west of the ACV, to 80 km at the outer limit of the ACV. In addition, depth conversion of the seis mic reflection data and unloading of the sediments indicate the presen ce of a regional depth anomaly of an extension similar to the lithosph eric thinning inferred from gravity modelling. The depth anomaly assoc iated with the swell, after correction For sediment weight, is about 5 00 m. We interpret the lithospheric thinning as an indication of rehea ting of old Mesozoic lithosphere beneath the Canary Basin and along wi th the depth anomaly as indicating a thermal rejuvenation of the litho sphere. We suggest that the most likely origin for the Canary Islands is a hot spot.