Contribution of multi-method geophysics to assess the regional setting of Bouillante Geothermal Province (Guadeloupe, West French Indies)

The Bouillante geothermal field is studied using multi-method geophysical data. This work presents a synthesis of all available, subaerial and marine, gravity and magnetic, electric and magnetotelluric data acquired during the last 30 years. Geophysical models have been initiated based on geological constraints and previous geophysical interpretations. The integration of the geophysical results has allowed us to build up an updated model of the geothermal system through layering information associated with petrophysical parameters, in agreement with the scheme of geothermal reservoirs. The distribution of resistivity with depth reveals the classical succession of resistive-conductive-resistive layers. The shallow resistive layer is well explaining in terms of massive and recent formations. The intermediate conductive layer marks the clay cover of the geothermal system, associated with low density and demagnetized rocks affected by hydrothermal alteration. Out of the geothermal area, the conductive body deepens and forms a pseudo-tabular layer, probably resulting of a regional phenomenon. Its shape could be inherited from a long period of meteoric (and/or hydrothermal) alteration. Lateral topographical and morphological indications suggest that its top may have acted as sliding surface during episodes of flank destabilization. The conductive layer would be then composed of both altered rocks and breccias within clayish matrix as observed on other volcanic islands. The later infilling of the valley form the upper resistive layer. The deep resistive layer is associated with dense formations older according to their depth. Based on our geophysical data and modeling, the geothermal reservoir could be more developed toward the north compared to the previously proposed extension. Moreover, a major volcano-structural control is evident since the faults seem to affect the internal structure of the Bouillante Province, and consequently the development of geothermal activity.