Abstract

The need to understand the structural context of the Bouillante geothermal field (West Basse-Terre, Guadeloupe, French West Indies) has led to onshore and offshore studies in the “high-energy geothermal fields” project, carried out by ADEME and BRGM. To ascertain the structural context of the island and the offshore continuation of the structures identified onshore, bathymetric, high-resolution reflection seismic and magnetic surveys were conducted on the shelf. The analyses of these detailed data show that the width of the present-day northwestern Basse-Terre shelf has been built by the accumulation of the Pleistocene detrital sediments over a volcanic substratum representing the prolongation on the shelf of an onshore volcanic edifice that bounds the Bouillante Bay on the south. The sedimentary cover has recorded two important regressive phases. Deciphering the structural frame has confirmed that the Bouillante sector is a key geodynamic area where the major tectonic and volcanic structures of the inner arc of the Lesser Antilles join. In this area, the N160° Basse-Terre volcanic axis, the N140° Montserrat-Bouillante volcanic and fault system, the EW Bouillante-Capesterre fault system, linked to the E-W-trending Marie-Galante graben, join up and their relationships have been specified. The N140°E Montserrat-Bouillante fault system ends on a N160° escarpment and basement high which would represent the relay of a major NNW-SSE- strike-slip fault system along the inner arc of the Lesser Antilles, linking the Montserrat-Bouillante fault to that of Les Saintes.

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