VEMANAUTE

Submersible study of the southern wall and the axial valley of the Vema Fracture Zone. Section of upper mantle and oceanic crust. Abstract: Tera Nova, 2(1): 68-73 The MAR-Vema Fracture Zone intersection surveyed by deep submersible Nautile Jean-Marie Auzende 1 , Daniel Bideau 1 , Enrico Bonatti 2 , Mathilde Cannat 3 , José Honnorez 4 , Yves Lagabrielle 5 *, Jacques Malavieille 6 , Vassilios Mamaloukas-Frangoulis 3 Catherine Mével 7 One of the two objectives of the Vemanaute cruise of the French deep submersible Nautile, was the geological study of the eastern intersection area between the Mid-Atlantic Ridge (MAR) and the Vema Fracture Zone in the equatorial Atlantic. Fourteen dives were conducted that allowed detailed geological survey and sampling of the main morphostructural units of this area: the northern and southern walls of the fracture zone, the median ridge, the northern and southern troughs and the nodal basin. In situ observations of recent tectonic features such as furrows, ridges and circular depressions, concentrated within the southern trough, allowed us to establish the location and the size of the present-day displacement zone. Geological investigations have shown that the nodal basin is entirely floored by basalts thus contrasting with other equivalent areas such as the Kane and Oceanographer fracture zone-MAR eastern intersections. Finally, this study stresses the great opposition between the relatively old and tectonically inactive northern part of the fracture, and the southern part which shows active tectonics and recent volcanic activity.