Estiramiento paralelo a los ejes de los pliegues en la Unidad de las Nieves (Dominio de Alborán, Béticas Occidentales)

Résumé

Stretching parallel to the orogenic grain is a basic mechanism in the kinematics of orogenic arcs. In the present work, we analyze the case of the Frontal Units, located at the outermost internal zones of the Betic Chain, within the western part of the Gibraltar Arc. We focus specifically on the Nieves Unit, whose internal structure is a NW-vergent recumbent syncline. Our results indicate that parallel stretching develops pervasively, with different modes depending on the deformation conditions. In this regard, stretching is mainly ac-commodated by veins in the right-side-up limb of the major syncline, whereas it is accommodated by boudinage in the overturned limb. The kinematic features of the minor folds also indicate differences in the dominant folding mechanism, which seems to be flexural slip and/or flow in the right-side-up limb, and post-buckling flattening in the overturned limb. Strain localization in the SE of the unit points to the overturned limb shearing by overthusting of the Alpujarride and Malaguide complexes upon the Nieves Unit. Moreover, parallel stret-ching could have been forced by the outward divergent thrusting directions around the western part of the Gibraltar Arc.