3-D Magnetotelluric Investigations for Geothermal Exploration in Martinique (Lesser Antilles). Characteristic Deep Resistivity Structures, and Shallow Resistivity Distribution Matching Heliborne TEM Results

Nicolas Coppo (1) , Jean-Michel Baltassat (1) , Jean-François Girard (1) , Pierre Wawrzyniak (1) , Sophie Hautot (2) , Pascal Tarits (2) , Thomas Jacob (1) , Guillaume Martelet (1) , Francis Mathieu (1) , Alain Gadalia (1) , Vincent Bouchot (1) , Hervé Traineau (3)

1 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)
2 UBO - Université de Brest
3 CFG - Compagnie Française de Géothermie

Within the framework of a global French program oriented towards the development of renewable energies, Martinique Island (Lesser Antilles, France) has been extensively investigated (from 2012 to 2013) through an integrated multi-methods approach, with the aim to define precisely the potential geothermal ressources,previously highlighted (Sanjuan et al., 2003). Amongst the common investigation methods deployed, we carried out three magnetotelluric (MT) surveys located above three of the most promising geothermalfieldsof Martinique, namely the Ansesd'Arlet, the MontagnePelée and the Pitons du Carbet prospects. A total of about 100 MT stations were acquired showing single or multi-dimensional behaviors and static shift effects. After processing data with remote reference, 3-D MT inversions of the four complex elements of MT impedance tensor withoutpre-static-shift correction, have been performed for each sector, providing three 3-D resistivity models down to about 12 to 30 km depth. The sea coast effect has been taken into account in the 3-D inversion through generation of a 3-D resistivity model including the bathymetry around Martiniquefrom the coast up to a distance of 200 km. The forward response of the model is used to calculate coast effect coefficients that are applied to the calculated MT response during the 3-D inversion process for comparison with the observed data. 3-D resistivity models of each sector, which are inherited from different geological history, show 3-D resistivity distribution and specificities related to its volcanological history. In particular, thegeothermal field related to the MontagnePeléestrato-volcano, is characterized by aquasi ubiquitous conductive layer and quite monotonic typical resistivity distribution making interpretation difficultin terms of geothermal targets. At the opposite, the resistivity distribution of Ansed'Arletareais radically different and geothermal target is thought to be connected to a not so deep resistive intrusion elongated along a main structural axis. Beside these interesting deep structures, we demonstrate, after analyzing the results of the recent heliborne TEM survey covering the whole Martinique, that surface resistivity distribution obtained from 3-D inversion reproduce faithfully the resistivity distribution observed by TEM. In spite of a very different sampling scale, this comparison illustrates the ability of 3-D MT inversion to take into account and reproduce static shift effects in the sub-surface resistivity distribution.

Mots clés: Magnetotelluric; 3-D inversion; Montagne Pelée; Ansesd'Arlet; Martinique; TEM; Geothermal exploration

Domaines: Sciences de la Terre; Géophysique [physics.geo-ph]

Nicolas Coppo, Jean-Michel Baltassat, Jean-François Girard, Pierre Wawrzyniak, Sophie Hautot, et al.. 3-D Magnetotelluric Investigations for Geothermal Exploration in Martinique (Lesser Antilles). Characteristic Deep Resistivity Structures, and Shallow Resistivity Distribution Matching Heliborne TEM Results. IRENA Meeting on Island Energy Transitions, Jun 2015, Fort-de-France, France. ⟨hal-01162414⟩