The Concept of Exhumed Analogue for Characterization of High-Energy Geothermal Reservoir: an Example from Les Saintes Island (Guadeloupe Archipelago, Lesser Antilles) and Consequences for Exploration

Abstract

The recognition of a fossil equivalent of the active geothermal system of the Basse-Terre Island in Guadeloupe archipelago (Lesser Antilles arc) in Terre-de-Haut Island (Les Saintes archipelago) allow us to better constrain the structure, the mineralogy and the petrological characters of the deep parts of an active geothermal reservoir. First, we demonstrate the occurrence, in Terre-de–Haut Island, of an exhumed analogue of the deeper parts of the current Bouillante geothermal field. In this exhumed paleo-geothermal reservoir we characterize the nature and the P-T evolutions of the hydrothermal mineral associations in relation with fluids transfers. Moreover, high-temperature hydrothermal activity is coeval with the development of ductile tectonic structures, particularly schistose corridors, and is dated at 2.59 ± 0.12 Ma on white micas, involving maximum activity of 600 ky. These data provide a conceptual model, including brittle-ductile transition located at a depth between 2.5 and 4 km. In this way, brittle and ductile tectonic structures are efficient drains to connected vertical and lateral fluids and heat transfers. This may provide new guides for exploration of geothermal resources in volcanic arcs.