Dimensionality Analysis of the Iberian Pyrite Belt Lithosphere derived from the Magnetotelluric Impedance Tensor.

The Iberian Pyrite Belt (IPB) hosts one of the largest concentrations of massive sulfide deposits in Europe, yet its lithosphere architecture remains incompletely understood. In this study, we employ magnetotelluric (MT) impedance tensor data to investigate the dimensionality and structural characteristics of the IPB crust. The analysis combines two complementary approaches: WAL invariants, computed from the MT impedance tensor using the Waldim code (Martí et al., 2013), which are scalar, rotation invariant quantities providing a robust, frequency dependent measure of three-dimensionality and highlighting anisotropic features in the conductivity distribution; and the Phase Tensor, following the methodology of Caldwell et al. (2004), which offers distortion free insights into the orientation and geometry of regional conductive structures. Integrating these methods enables a systematic dimensional analysis of the impedance tensor, revealing lateral heterogeneities, preferred orientations of conductive features, and depth dependent variations in lithospheric responses.

The results demonstrate that WAL invariants and Phase Tensor analysis together allow the separation of near surface distortions from deeper geoelectric structures, providing a robust framework for characterizing the lithospheric architecture of the IPB. This study highlights the enhanced resolution and robustness achieved by complementing the tensor based analysis of MT data with invariant derived quantities that provide rotationally independent measures of three-dimensionality and anisotropy.

Consequently, this dimensional and structural assessment constitutes a critical prerequisite for subsequent MT data inversion, as it provides essential constraints on model dimensionality, structural orientation, and the treatment of near surface distortion. By supporting the choice between 2D and 3D inversion strategies, the proposed framework enhances the stability of the inversion process, increases the reliability of the conductivity distributions, and ensures greater geological consistency of the resulting models.

Acknowledgment

This work is supported by FCT, I.P./MCTES through national funds (PIDDAC): LA/P/0068/2020, https://doi.org/10.54499/LA/P/0068/2020,UID/50019/2025,  https://doi.org/10.54499/UID/PRR/50019/2025, UID/PRR2/50019/2025

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