Electrical signature of modern and ancient tectonic processes in the crust of the Atlas mountains of Morocco

► Newly acquired magnetotelluric data image the electrical resistivity distribution of the crust from the Middle Atlas to the Anti-Atlas, crossing the tabular Moulouya plain and the High Atlas. ► The main scientific contribution of this work is a new electrical resistivity distribution at crustal sc...

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Veröffentlicht in:Physics of the earth and planetary interiors 2011-04, Vol.185 (3), p.82-88
Hauptverfasser: Ledo, Juanjo, Jones, Alan G., Siniscalchi, Agata, Campanyà, Joan, Kiyan, Duygu, Romano, Gerardo, Rouai, Mohamed
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Sprache:eng
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Zusammenfassung:► Newly acquired magnetotelluric data image the electrical resistivity distribution of the crust from the Middle Atlas to the Anti-Atlas, crossing the tabular Moulouya plain and the High Atlas. ► The main scientific contribution of this work is a new electrical resistivity distribution at crustal scale for the whole system. ► The most striking result is the presence of two low resistivity anomalies at lower crustal depths. ► One is located below the Moulouya plains an area showing other geophysical anomalies that we have associated to the presence of small amounts of partial melting. ► In the Anti-Atlas the low resistivity anomaly found is the first reported geophysical anomaly at lower crustal depths. The Atlas Mountains in Morocco are considered as type examples of intracontinental mountain chains, with high topography that contrasts with moderate crustal shortening and thickening. Whereas recent geological studies and geodynamic modelling suggest the existence of dynamic topography to explain this apparent contradiction, there is a lack of modern geophysical data at the crustal scale to corroborate this hypothesis. To address this deficiency, magnetotelluric data were recently acquired that image the electrical resistivity distribution of the crust from the Middle Atlas to the Anti-Atlas, crossing the tabular Moulouya plain and the High Atlas. All tectonic units show different, distinct and unique electrical signatures throughout the crust reflecting the tectonic history of development of each one. In the upper crust, electrical resistivity values and geometries can be associated to sediment sequences in the Moulouya and Anti-Atlas and to crustal scale fault systems in the High Atlas developed likely during Cenozoic times. In the lower crust, the low resistivity anomaly found below the Moulouya plain, together with other geophysical (low velocity anomaly, lack of earthquakes and minimum Bouguer anomaly) and geochemical (Neogene-Quaternary intraplate alkaline volcanic fields) evidences, infer the existence of a small degree of partial melt at the base of the crust. Resistivity values suggest a partial melt fraction of the order of 2–8%. The low resistivity anomaly found below the Anti-Atlas may be associated with a relict subduction of Precambrian oceanic sediments, or to precipitated minerals during the release of fluids from the mantle during the accretion of the Anti-Atlas to the West African Supercontinent during the Panafrican orogeny (ca. 685 Ma).
ISSN:0031-9201
1872-7395
DOI:10.1016/j.pepi.2011.01.008