Publication 129
Electrical signature of modern and ancient tectonic processes in the crust of the Atlas mountains of Morocco
Ledo, J., A.G. Jones, A. Siniscalchi, J. Campanyà, D. Kiyan, G. Romano, M. Rouai and TopoMed MT Team
Abstract
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 Mouluya plain, together with other geophysical (low velocity anomaly,
lack of earthquakes and minimum Bouguer anomaly) and geochemical (Neogene-Quaternary
intraplate alkaline volcanic fields) evidence, 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% to 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).
Source
Physics of the Earth and Planetary Interiors, 185, 82-88, doi: 10.1016/j.pepi.2011.01.008..
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Alan G Jones / 04 May 2011 /
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