A MULTIDISCIPLINARY GEOPHYSICAL-STUDY IN THE BETIC CHAIN (SOUTHERN IBERIA PENINSULA)

The combined analysis of magnetotelluric measurements, tomographic vel ocity models and deep seismic reflection images confirms that the Beti cs orogen consists of the juxtaposition of two crustal domains charact erized by distinctive physical properties. At depth these data sets sh ow evidence for a non-coincidence of the petrological and the seismic Moho beneath the Betics chain. The data sets reveal the geophysical pr operties of the Alboran domain (Internal Betics) and the Iberian Massi f (External Betics). According to this, the Iberian crust features a r elatively high seismic velocity, is seismically transparent in the sei smic reflection images and is electrically resistive. The Alboran doma in crust is characterized by a low average velocity, displays high ref lectivity in the seismic reflection images and is electrically conduct ive. The outcrops of the metamorphic complex (Alpujarride and Nevado F ilabride), showing relatively high velocities coupled with low V-p/V-s values (1.67) derived from the Wadati slopes, suggest the existence o f rocks rich in silica beneath the Alboran domain crust. An interprete d detachment at 12 km depth imaged by deep seismic reflection suggests that these rocks could be related to the Iberian upper crust. partial melts and fluids are proposed to explain the high conductivity observ ed at deep crustal levels. These would account also for the reflectivi ty and the low V-p/V-s ratios mapped beneath the Alboran domain. (C) 1 998 Elsevier Science B.V. All rights reserved.