STRESS AND PALEOSTRESS IN THE BETIC-RIF CORDILLERAS (MIOCENE TO THE PRESENT)

Palaeostress orientation in the Betic-Rif cordilleras can be determine d for the Miocene to the Quaternary by analysis of brittle microstruct ures (faults, joints, striated pebbles and stylolites). In the central and northern South Iberian Domain, sigma1 was subhorizontal and trend ed NW-SE, from the Early Miocene to the present. In the northern Albor an Domain, from the Burdigalian to the Serravallian, palaeostress elli psoids were oblate, with sigma3 subhorizontal and trending ENE-WSW. In the southern part of the South Iberian Domain and in the northern par t of the Alboran Domain (Betic Cordillera) from the Tortonian to the Q uaternary, palaeostress ellipsoids were variable: in the Granada regio n. they were prolate with sigma1 subvertical; but in the Almeria regio n they were triaxial with sigma2 subvertical and sigma3 subhorizontal and trending NE-SW to E-W. In the Rif, the Alboran and African-Maghreb ian domains were affected by palaeostresses with sigma1 subhorizontal, varying from NE-SW in Tortonian times to N-S in the Plio-Quaternary. A study of earthquake focal mechanisms by the right-dihedra method ind icates that the present-day general stress field around the Betic-Rif cordilleras is compressional, with sigma1 subhorizontal and trending N W-SE. In the Betic Rif cordilleras, this general stress field is modif ied and the present-day orientations of sigma1, sigma2 and sigma3 are nearly the same as those of the palaeostresses in the Pliocene and Qua ternary. The distribution and evolution of stresses in the Betic-Rif c ordilleras, from the Miocene to the present, can be correlated with th e main Neogene deformations: extensional structures in the central and northern Alboran Domain and the southern part of the South Iberian Do main, and compressional structures in the South Iberian and African-Ma ghrebian domains and in the southern part of the Alboran Domain.