A Geological Interpretation of the Gibraltar Arc System Based on New Seismic Reflection Images, Wide-angle Seismic Velocity Models, and Marine Magnetoteluric data Modeling

César R. Ranero, Eulàlia Gràcia, Xavier Garcia, and Ingo Grevemeyer

The region of the Gibraltar Arc System (GAS) between Africa and Iberian Peninsula is currently dominated by the collision between the Eurasian and African plates. The recent deformation is mainly driven by the NW–SE, slow 4-5 mm/yr convergence that is partitioned across numerous faults causing the strain to be distributed in a diffused swath across a broad region with no clear well-defined plate boundary.

However, the GAS is also characterized by four large-scale geological units with a structure that appears unrelated to current plate kinematics. The GAS is 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 several extensional basins in the Mediterranean portion of the region. The Western Alboran Basin is located on the rear of the Gibraltar stacked units, and displays littledeformed sediment infill. The Eastern Alboran Basin is characterized by numerous ridges and promontories that appear volcanic in origin and it is possibly transitional in nature to the South Balearic – North Algerian Basin with a generally lower relief.

Those different tectonic elements are floored by poorly known basement, and their age, evolution and geodynamic origin are still debated. The uncertainty arises from the lack of deep-penetration modern geophysical data in much of the region. In the last 6 years, 4 successive experiments have produced an extensive coverage of the structures of those geological units. In 2006 the WestMed cruise with German R/V Meteor collected five 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 collected deep reflection images across the South Balearic, West and East 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 contribution is to present a summary of all observations collected in the 4 experiments. 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 and sedimentary structures. We will also present an interpretation of the GAS in the context of a geodynamic model of eastward Miocene subduction, and Plio-Quaternary continent collision that might explain the crustal-lithospheric structure observed with the 4 experiments.

AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013