P. Schmoldt, PhD - MTNet - DIAS

Abstract
The Tajo Basin and Betic Cordillera are the areas investigated by the first phase of the
PICASSO (Program to Investigate the Convective Alboran Sea System Overturn) project
in south-central Spain. The magnetotelluric (MT) component of PICASSO Phase I provides
information about the electric conductivity distribution in previously unprobed subsurface
regions, as well as enhancing results of prior geological and geophysical investigations,
thereby enabling the devise of a petrological subsurface model and a comprehensive
understanding about the tectonic setting.
During analysis of the MT data, oblique geoelectric strike directions were determined
for the Tajo Basin subsurface, which causes severe artefacts in models from commonly
applied isotropic two-dimensional (2D) inversion, or requires computationally expensive
three-dimensional (3D) inversion. A novel approach is developed in this thesis, which
utilises electric anisotropy in one-dimensional (1D) and 2D inversions to image oblique
2D subsurface structures. Computational expense of this approach is considerably lower
and its performance is successfully tested in a synthetic model study and subsequently
employed to derive a model of the Tajo Basin subsurface.
In addition to the novel anisotropic approach, isotropic 2D and 3D inversions are used
to obtain enhanced insight into Iberian subsurface geology. The most striking features
of the model are (i) a distinct vertical interface in the centre of the Tajo Basin that is
associated with the “Alpine Spain” – “Variscan Spain” boundary; (ii) a mid- to lower
crustal anomaly that is related to remnants of asthenospheric intrusion in connection with
Pliocene volcanic events in the Calatrava Volcanic Province; (iii) a low resistivity – low
velocity feature in the Tajo Basin lithospheric-mantle, related to the extensive reservoir
responsible for volcanic events throughout Europe and Morocco. For the latter two, effects
of hydrous phases are inferred that may originate from dehydration processes at the
subducting slab beneath Alboran Domain and Betics Cordillera.
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