Crustal Imaging of Portugal Mainland Using Magnetotelluric Data

The comprehensive mapping of resistivities in depth and its interpretation is of great importance to unravel the electrical properties of deep-seated rocks, providing significant insights into the structure of the crust. The first 3D resistivity model for Portugal mainland is here reported using data from 31 broadband MT soundings spaced 50 x 50 km apart. The model shows large crustal volumes with contrasting resistivity values. The central and northern regions are characterized by a high resistivity crustal domain spreading in-depth (10(3)-10(5) Omega.m) that correlates well with voluminous granitoid bodies and high-grade metamorphic rocks. To the west and the south, roughly corresponding to the Portuguese Western Shore and the South Portuguese Zone (SPZ) respectively, the crustal resistivity tends to decrease unevenly to values between 1 and 10(3) Omega.m. Interconnected graphite in structural discontinuities, possibly forming a regional mid-crustal decollement at similar to 13-15 km depth, are highlighted by multiple low resistivity crustal domains (1-100 Omega.m). Similarly, the model reveals a very large E-W low resistivity crustal domain in SPZ possibly representing a deep-seated major decollement. The present study aims to contribute to a better understanding of the physical properties characterizing the concealed crust in Portugal mainland, providing also indirect information on its composition and structure. Plain Language Summary Portugal is located in the western part of Europe and most of its geological background is part of the Iberian Massif, an ancient block of continental lithosphere composed of several geotectonic units that differ in rock composition and structure. The geological characteristics of these main units, as well as the structures that separate them, potentially generate distinctive geoelectric signatures. Over the years, most electromagnetic surveys have been carried out on a regional scale. The focus has always been on the specific features of certain zones of the Portugal mainland, so it has not been possible to obtain a complete picture of the large-scale structures that extend over the entire crust, especially in the northern part of the country. Therefore, the 3D resistivity model obtained through an electromagnetic method called Magnetotelluric (MT), allows us to have a complete image of the crust up to similar to 40 km deep. The results contribute to a better characterization of the crust and reveal that the crustal segment extending beneath the central and northern regions of the Portuguese mainland is much less heterogeneous than its southern counterpart, providing important information to issues addressed in various fields of geosciences (e.g., Space Weather, Mineral, and Hydrocarbon exploration).