[1] The Atlas Mountains are characterized by high elevations and Quaternary volcanism. Long period magnetotelluric data acquired along a NNW-SSE transect reveal the presence of a conductive anomalous mantle below the High Atlas. Data dimensionality analyses show a preferent N80°E strike of the deep resistivity structure in agreement with the induction vector alignment at long periods. Accordingly, a 2D inversion of the data set was carried out. Large resistive bodies at the crustal basement most likely correspond to batholiths emplaced in more conductive metapelites. They are covered by outcropping conductive sedimentary detritic and carbonate rocks. Lithospheric thinning producing anomalous mantle and basin development in the Atlas probably started during Triassic-Jurassic rifting. Inversion tectonics since the Oligocene produced low shortening on previous lithospheric weak zones, with thrusting of the Atlas above the stable African plate. Melting at the top of the anomalous mantle is connected with Quaternary basaltic volcanism in the Middle Atlas.

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[1] Eight independent magnetotelluric (MT) campaigns, carried out in the western Mediterranean area and Antarctica, have been analyzed with the aim of extracting information from Schumann resonances (SR). The advantages and drawbacks of MT data with respect to single-purpose fixed stations for SR research are evaluated. Two different methods of signal processing have been employed: spectral analysis through the fast Fourier transform (FFT) and Rescaled Range analysis (R/S), calculating the Hurst exponents. The first permitted a study of the source contributions, the effects caused by local changes in the observation area, interseasonal behavior, and the relations between electric and magnetic horizontal fields. The average central frequencies obtained for the first three resonances are 7.8, 14, and 20.5 Hz respectively, but there are fluctuations in them. These variations seem to respond to the characteristics of the principal active storms that generate the resonances. These frequency shifts are stronger for the second and third resonances. Owing to the broadband registering of MT, the second method of signal processing could be applied to the low noise signals from Antarctica with high resolution, revealing the persistent nature of SR. A numerical simulation indicates a way for inferring lightning rates from R/S analysis.

Mélange rocks outcrop widely in the central and western frontal sectors of the Betic Cordillera, as in many other collisional orogens where they form part of the accretionary wedges. Extrusion of Triassic plastic clays and evaporites was favored by the progressive accretion of the Betic External Zones, mixing rocks of different provenance and forming a synorogenic frontal mélange unit. MT data coupled with gravity data are a valid combined methodology to characterize the geometry of these mélange units, since the characterization of plastic rocks geometry is usually uncertain using seismic techniques. The results correlate well with known geological features (sedimentary basins, calcareous ranges, evaporitic rocks) and reveal the deep geometry. A resistive body, slightly dipping toward the SE, points to the continuity of the Iberian Massif below the Guadalquivir basin (2°) and the External Zones (6–8°). To the south, gravity models show the Iberian continental crust subducting below the Internal Zones with a roughly 20–35° slope. The main conductive bodies are related to the location of evaporitic rocks involved in the frontal mélange. They overlie the Iberian Massif and, southwards, the frontal Jurassic and Cretaceous limestone sequences of the External and Median Subbetics. In this setting, thick plastic rock units placed above the foreland could act as a lubricant facilitating continental subduction, and being progressively accreted toward a frontal mélange.

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