Magnetotelluric Imaging of the Lithosphere Across the Variscan Orogen (Iberian Autochthonous Domain, NW Iberia)

Abstract

A new magnetotelluric (MT) survey comprising 17 MT soundings throughout a 30 km long N30°W transect in the Iberian autochthons domain of NW Iberia (Central Iberian Zone) is presented. The 2‐D inversion model shows the resistivity structure of the continental crust up to 10 km depth, heretofore unavailable for this region of the Variscan Orogen. The MT model reveals a wavy structure separating a conductive upper layer underlain by a resistive layer, thus picturing the two main tectonic blocks of a large‐scale D2 extensional shear zone (i.e., Pinhel shear zone). The upper layer represents a lower grade metamorphic domain that includes graphite‐rich rocks. The lower layer consists of high‐grade metamorphic rocks that experienced partial melting and are associated with granites (more resistive) emplaced during crustal thinning. The wavy structure is the result of superimposed crustal shortening responsible for the development of large‐scale D3 folds (e.g., Marofa synform), later deflected and refolded by a D4 strike‐slip shear zone (i.e., Juzbado‐Penalva do Castelo shear zone). The later contribution to the final structure of the crust is marked by the intrusion of postkinematic granitic rocks and the propagation of steeply dipping brittle fault zones. Our study demonstrates that MT imaging is a powerful tool to understand complex crustal structures of ancient orogens in order to design future prospecting surveys for mineral deposits of economic interest.

New Detailed Modeling of GICs in the Spanish Power Transmission Grid

“…Aimed at improving our previous analyses on the threat posed by GICs to the Spanish grid, we have undertaken a critical review of the existing magnetotelluric (MT) data and models and created a new 3D Electrical Resistivity Model of the Iberian Lithosphere (ERMIL). Several local and regional 2D and 3D crustal and lithospheric electrical resistivity models had been obtained in the last 25 years (Alves Ribeiro et al., 2017; Campanyà et al., 2012, 2018; Carbonell et al., 1998; Garcia et al., 2015; Ledo et al., 2000; Marti et al., 2009; Monteiro Santos et al., 2002; Pous et al., 1995, 1997; 1999, 2004; Rosell et al., 2011). However, a lithospheric scale 3D model of the whole peninsula was still lacking.…”

Crustal Imaging of Portugal Mainland Using Magnetotelluric Data

“…(2004), and Alves Ribeiro et al. (2017). The remaining data from 21 MT stations collected during this study are available at Baltazar‐Soares et al.…”

“…Data from 10 MT soundings in the southern region of Portugal, carried out between 1997 and 2002, are attributed to Almeida et al (2001Almeida et al ( , 2005, Pous et al (2004), and Alves Ribeiro et al (2017). The remaining data from 21 MT stations collected during this study are available at Baltazar-Soares et al (2022).…”

“…The geological attributes of these main units, as well as of the first order structures that separate them, potentially generate distinctive geoelectrical signatures. The study area has been the subject of several electromagnetic surveys (Almeida et al., 2001, 2005; Alves Ribeiro et al., 2017; Farzamian et al., 2018; Monteiro Santos et al., 1995, 1999; Monteiro Santos, Mateus, et al., 2002; Monteiro Santos, Matos, et al., 2002; Muñoz et al., 2005, 2008; Pous et al., 2004; Vieira da Silva et al., 2007) and seismic surveys (Arroucau et al., 2021; Dündar et al., 2016; Prodehl et al., 1975; Simancas et al., 2001, 2003; Veludo et al., 2017). As a result of these surveys, discontinuous conductive strips in the mid‐crust were recognized, especially across the OMZ and SPZ, along with a possible regional crustal detachment at depths of ∼15 km.…”