261 9. Defining high enthalpy geothermal drilling target with multi-physics to low resolution and likely interference from seawater infiltration at the surface. Nevertheless, a resistivity contrast can be observed between the upper part of the basement and the lower part, where resistivity is slightly higher. This boundary is marked as a dark red line in Figure 9.5. It thus represents the basal boundary of a portion of the basement that may be partially clay-altered due to hydrothermal alteration, with its deepest levels likely containing the caprock. Finally, very low resistivity values, again below 10 Ω·m, are obtained at the bottom of the grid, towards the east. When placing this in the context of the reference conceptual model, it could correspond to the heat source of the geothermal system, located at around 12 km depth. Its roof is interpreted in the cross-sections (Figure 9.5), although the large depth introduces considerable uncertainty regarding its geometry. This interpretation work allows for the construction of a 3D model that includes the three main elements of the geothermal system (Figure 9.6). Figure 9.3 Resistivity map and cross-section on Petite Terre Island. On the map, black points: station location, black lines: location of cross-section, green line: SW-SE trend tendency. On cross-section, purple lines: limitation of resistive body.
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