Some features of the northwest African margin and magnetic quiet zone

Abstract

A smooth basement reflector drilled in D.S.D.P. / IPOD Site 367 as basalt extends throughout much of the magnetic quiet zone off North West Africa. Multichannel seismic lines show structures and layered rock complexes locally beneath this basalt reflector. Under the continental slope of Senegal and Mauritania, the basement reflexion is no longer distinguished beneath a Cretaceous carbonate front. Refraction profiles between the Cape Verde Rise and Mauritania and from Conception Bank to Morocco establish the existence of a 7.1 km/s layer at a depth of 14 km. Off Mauritania the smooth basement seems to merge with this layer. Diapiric salt basins existing under the continental rise are only resolved as velocity layers off Mauritania. No sharp boundary from continental to oceanic crust was deduced from the seismic data.