Resistivity and heterogeneity of earth crust in an active tectonic region, southern Tuscany (Italy).

Southern Tuscany, belonging to the inner zone of the Northern Apennines, is an ideal laboratory for observing the physical features of the lithosphere and their evolution in tectonically active regions. Here the crust is very thin, with a thickness of less than 25 km, and heat flow is very high, hence only very shallow depths of investigation are needed to investigate many of the middle-deep crustal features that are common to many other parts of the world. The magnetotelluric (MT) surveys performed in this region have provided information on the resistivity structure, which is related to the extent and distribution of free fluids and to the partial melts in the crust. The picture emerging from these MT surveys is that of a resistivity structure that is only partially related to the heat flow regime of the area. A very low resistivity was found below the vapor-dominated geothermal system of Larderello and below areas that have no clear connection to any geothermal system, whereas this reduction of resistivity is less conspicuous below the water-dominated geothermal system of Mt. Amiata.