The PICASSO project: MT Investigation in Southern Spain and Morocco - Results of phase I and outlook on phase II

PICASSO (Project to Investigate Convective Alboran Sea System Overturn) is an international, multi-disciplinary project that aims to improve knowledge of the internal structure and plate-tectonic processes in the highly complex three-dimensional region formed by the collision of the African and European plate under the effect of the Mediterranean plate motion. The first phase of the DIAS magnetotelluric (MT) component of the PICASSO project was carried out in Southern Spain from Sept.-Nov., 2007 focused on the investigation of the internal structure of the Betic Mountain Chain and the Iberian Basement. Two different types of magnetotelluric (MT) equipment - broadband (BBMT) and long period (LMT) MT - were used along a profile from the outskirts of Madrid to the Mediterranean Sea through the Betic Mountain Chain. The modified acquisition design of one of the equipment types (the LVIV LEMI long period system), with separate recording of each telluric channel, allowed for advanced investigation of the acquired dataset. The data were processed using four different robust algorithms, and the different responses have been compared. A distinct separation can be made between the Betics region of Alpine orogeny in the south and the Variscan Iberian Massif beneath the north of the profile in terms of their inherent electric conductivity characteristics. Models derived by two-dimensional inversions of regional responses, after removing distortion effects, from this first phase show a remarkably complex subsurface structure beneath the region of the External Betic Chain. Strike direction varies along the profile and with depth due to the intricate morphology, and its choice has significant impact on the responses to be modelled and thereby provides a challenging framework for MT data interpretation. The second phase of PICASSO aims to shed light onto the origin of the Atlas Mountain Chain and test hypotheses for its missing mantle root derived from heat flow, gravity, geoid and topography observations. The MT investigation scheduled for the period end-September to end-November comprises two long period profiles, N-S through Meknes and NW-SE through Marrakesh. Additional broadband surveys will be carried out at the same time in collaboration with partners from the Universities of Barcelona and Bari in order to investigate the crustal structure of the Atlas Mountains.