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

Abstract

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. Copyright © 1991, Wiley Blackwell. All rights reserved