A high electrical conductive zone at lower crustal depth beneath the Betic Chain (Spain)

Abstract

Magnetotelluric data with periods of up to 2000 s were collected and the conductivity structure of the crust and upper mantle was imaged in the Central Betic chain. Interpretation of the impedance tensor components and the geomagnetic transfer functions was made in terms of a two-dimensional resistivity model along a NW–SE profile from the Guadalquivir foreland basin and across the boundary between the External and the Internal Betics. Elongated high conductivity zones in the upper and middle crust related to fluid circulation along both sediments and faults were detected. The conductors in the upper crust coincide with the areal distribution of the Cenozoic and Mesozoic sedimentary rocks from the Guadalquivir basin and the External Betics and the conductors in the middle crust with the major Miocene extensional detachments affecting the basement rocks of the Internal Betic zone. A high conductivity zone at lower crustal levels beneath the outer Internal Betics was also detected next to an area where earlier seismic reflection data had imaged a duplication of the reflective Moho. This conductor was interpreted as partial melting of a southeast dipping subducted Iberian lower crust. The geodynamic significance of this subduction depends mainly on whether the overthrusting lower crust belongs to the Alboran domain or to the Iberian plate. In the former case it would correspond to a major plate boundary and in the latter to an intraplate feature.