Chapter 3 - Azores–Tunisia, A Tectonically Complex Plate Boundary

Abstract

Abstract The seismically active region from Tunisia to the Azores Islands constitutes the westernmost part of the plate boundary between Eurasia and Africa. From the point of view of tectonics, this is a complex structure which involves volcanism and rifting at the Azores, strike-slip motion at the center of the Atlantic, and horizontal N-S compressions at its eastern part, with complex interaction between Iberia and northern Africa and E-W extension at the Alboran Sea, involving some kind of subduction or delamination process. This chapter has been divided into four parts: (1) Atlantic region, Azores–Gibraltar; (2) Azores Islands triple junction; (3) southern Iberia, Betics, and Alboran Sea; and (4) North Africa, Morocco, Algeria, and Tunisia. Plate motion shows counterclock rotation of Africa with respect to Eurasia around a pole near the Canary Islands. The Azores region forms a triple junction with ridge structure and oblique spreading in its three branches. The Atlantic region from Azores to Gibraltar is separated into two parts, west and east of 20°W. The first has E-W strike-slip motion and the second is under horizontal N-S compression producing underthrusting of Africa. The Betics–Alboran area is dominated by the collision movement between Iberia and northern Africa, and the E-W extension at the Alboran Basin. Intermediate and deep earthquake activity and tomography data show an anomalous deep structure, interpreted as produced by a subduction or a lithospheric delamination process. The Betics Cordillera, which links with the Rif by the Gibraltar Arc, is formed by overthrusting toward the north, limiting with the stable Iberia, and crossed by several fracture systems. The Rif, High Atlas, and Tell mountains are under NW-SE horizontal compression and dominated by structures trending NE-SW. Several interpretations have been given to the tectonic development of these regions, and some aspects are not yet completely explained.