Sampling and observation of oceanic mantle and crust on Gorringe Bank

Abstract

THE structure and nature of the uppermost oceanic mantle and crust has been, and still is, the subject of a major international research effort1. Yet the direct field evidence known to us on this subject, whether obtained by drilling in the I.P.O.D. oceanic crust programme2 or by submersible surveying in the Famous programme3, has been either very incomplete or limited to the upper part of layer 2. As a result, the problem of the comparison between ophiolites and oceanic crust is still debated1. We report here the preliminary results of an in situ geological survey in which we have sampled and observed what we believe to be an almost complete geological section starting a few kilometres below the Moho discontinuity and ending in the upper part of layer 2 (ref. 4). This section outcrops on the flanks of Gorringe Bank, which is a ridge 200 km long and 60 km wide between Tagus and Horseshoe abyssal plains in the Atlantic ocean, South West of Cape Saint Vincent, Portugal (Fig. 1).