Formation and deformation of the Western Mediterranean basins

Abstract

PART 2: Seismic reflection Images, wide-angle seismic velocity models, and magnetoteluric structure of the Gibraltar Arc system: A geological interpretation of the geodynamic origin of Gulf of Cadiz imbricated wedge, the Alborán basin, and the South-Balearic basin The geodynamics of the region of the Gibraltar Arc system between north Africa and the Iberian Peninsula are currently dominated by the collision between the Eurasian and African plates. The ongoing deformation is mainly driven by the NW–SE, slow 4-5 mm/yr convergence that is partitioned across numerous faults causing that the strain is distributed in a diffused swath across a broad region with no clear well-defined plate boundary. However, the Gibraltar Arc system is characterized by a series of main geological units with a structure that appears that might be unrelated to the current dominant plate kinematics. The Gibraltar Arc system is formed by an arcuate structure that is fronted in the west by a large imbricated wedge of tectonically piled sediment slices in the Gulf of Cadiz, and a series of basins in the Mediterranean portion of the region. The western Alboran basin displays little deformed sediment infill located on the rear of the Gibraltar stacked units. The eastern Alboran basin is characterized by numerous ridges and promontories that appear volcanic in origin and it is possibly transitional to the South Balearic – North Algerian basin that displays a generally lower topography. Those different tectonic elements are floored by poorly known crystalline basement and their age, evolution and geodynamic origin are still strongly debated. Part of the uncertainty arises from the lack of deep penetrating modern geophysical data in much of the region. In the last 6 years, Four successive experiments in the region have produced an extensive coverage of the structures of the different tectonic units. In 2006 the WestMed cruise with German R/V Meteor collected a series of wide angle seismic profiles in the eastern Alboran and South Balearic basins. Two multichannel seismic reflection cruises with the R/V Sarmiento de Gamboa in 2011 (TopoMed-Gassis cruise) and (Geomargen-1 cruise) collected deep reflection images across the South Balearic, Alboran and Gulf of Cadiz. Two marine magnetotelluric cruises in the Alborán basin (Amelie project) collected complementary data in 2009 and 2011. The goal of this seminar is to present a summary of all observations collected in the 4 experiments that have not yet been published. We will discuss the meaning of the wide-angle seismic P-wave velocity models across key regions of the system and the new reflection images of the tectonic structures and sedimentary basins. We will also present a preliminary interpretation of the Gibraltar Arc system in the context of a geodynamic model of eastward Miocene subduction, currently inactive, that might explain many of the structures observed in the 4 experiments.