Crustal Imaging of Portugal Mainland Using Magnetotelluric Data

Abstract

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 × 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 Ω.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 Ω.m. Interconnected graphite in structural discontinuities, possibly forming a regional mid-crustal décollement at ≈13–15 km depth, are highlighted by multiple low resistivity crustal domains (1–100 Ω.m). Similarly, the model reveals a very large E-W low resistivity crustal domain in SPZ possibly representing a deep-seated major décollement. 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.