CRUSTAL STRUCTURE OF THE MADEIRA-TORE RISE, EASTERN NORTH-ATLANTIC - RESULTS OF A DOBS WIDE-ANGLE AND NORMAL INCIDENCE SEISMIC EXPERIMENT IN THE JOSEPHINE SEAMOUNT REGION

During November-December 1988, an extensive geophysical data set was collected over the Josephine Seamount, which is located at the northeasterly end of the Madeira-Tore Rise in the eastern North Atlantic. The Josephine Seamount lies at the intersection of the Madeira-Tore Rise and Azores-Gibraltar Fracture Zone, the latter representing the Africa-Eurasia plate boundary in this part of the eastern North Atlantic. From this data set, a 275 km long explosive refraction line has been modelled together with wide-angle airgun profiles, seismic reflection and gravity data. The velocity-depth model shows that the crust either side of the Seamount is typically oceanic in character. However, beneath the Seamount there exists a region of anomalously high velocity and crustal thickening to a depth of about 17-18 km. Gravity modelling also suggests that the Josephine Seamount is compensated by a crustal root, and that the Josephine Seamount/Madeira-Tore Rise system is in local isostatic equilibrium. Calculations of the flexural rigidity and effective elastic thickness of the lithosphere in this region suggest that the Madeira-Tore Rise formed contemporaneously with the lithosphere on which it lies. This age of crustal loading is consistent with the proposal that the Madeira-Tore Rise is an aseismic ridge which formed at or near the Mid-Atlantic Ridge.