Gravity and Resistivity Surveys in Hydrothermal Modeling (S. Miguel - Azores)

Abstract

Several resistivity and gravity surveys, performed in the central part of the S. Miguel (Azores) island as a contribution to built up the hydrothermal model associated to the Agua de Pau volcano, are presented in this paper. The resistivity data inversion points out the existence of a fault system, related to a collapsed caldera, located close to the summit and in the northern flank of the do Fogo. Through this fault system, the hydrothermal fluid would ascend and in a second phase would circulate northwards, constrained by the NNW-SSE fault system connected to the Ribeira Grande graben, towards Ribeira Grande geothermal field area. The NE-SW fault systems, crossing the above mentioned NNW-SSE one, northwards of the Ribeira Grande calderas and Vermelho, would play an important role in the flow path of the geothermal fluid. A low density body, located in the top kilometres of the crust, suggests the existence of a geothermal reservoir, beneath the summit of the Agua de Pau volcano apparatus. So, the infiltrated meteoric would be warmed up and forced to ascend, constrained by the fault systems crossing the main edifice of the volcano.