Deep deformation pattern from electrical anisotropy in an arched orogen (Betic Cordillera, western Mediterranean)

Abstract

Long-period magnetotelluric data acquired in the Iberian Massif and the Betic Cordillera arched orogen provide the first evidence of electrical anisotropy in the upper mantle of the Mediterranean region. Strike analysis at different periods reveals preferred structure orientation related to olivine elongation in the mantle, and points to a heterogeneous anisotropy pattern. At deep levels (periods ≥104 s), all the sites show a common north-south geoelectrical strike (∼N170°E), which may represent a low-intensity deformation, possibly related to “frozen” prealpine plate tectonics. For periods between 10 and 103 s, a north-south constant strike (∼N180°E) at the Betic Cordillera sites contrasts with the east-west strike (∼N85°E) in the Iberian Massif. An increase in the magnitude of the induction arrows from the Iberian Massif to the inner part of the Betic Cordillera probably reflects higher deformation toward the axis of the Eurasian-African plate boundary. The integration of electrical anisotropy data with seismic anisotropy allows us to discuss mantle deformation patterns produced by delamination and subduction, suggesting that the latter mechanism may be more suitable for the alpine evolution of the western Gibraltar Arc.