En la Zona Externa de la Cordillera Bética los materiales Triásicos presentan facies bechoides y estructuras complejas que no son fáciles de interpretar. En ocasiones se puede interpretar que en los afloramientos de facies yesíferas triásicas existen tanto facies resedimentadas (olistostrómicas) del Cenozoico como diapíricas. No obstante, estudios más recientes hacen pensar más en los factores tectónicos como determinantes de las estructuras geológicas presentes en gran parte de la Zona Externa de la Cordillera. Aunque la expresión de gran parte de estas brechas/megabrechas están condicionadas por la presencia de evaporitas y por su comportamiento plástico, la estructura geológica final está marcada por una tectónica marcada por extensas zonas de falla con una componente importante de salto en dirección, posterior a una tectónica de mantos y a una tectónica salina preorogénica.
Tectonics, 36, 1006–1036 (2017).
An evaporite‐bearing accretionary complex in the northern front of the Betic‐Rif Orogen
F. Pérez-Valera, M. Sánchez-Gómez, A. Pérez-López, L.A. Pérez-Valera
https://doi.org/10.1002/2016TC004414
ABSTRACT
The Guadalquivir Accretionary Complex forms a largely oblique prism at the northern edge of the Betic-Rif orogen, where Miocene sediments plus allochthonous evaporite-bearing units were accreted during the displacement of the Alborán Domain toward the west. Traditional interpretations end the tectonic structuring of the Betic Cordillera at the present topographic front, beyond which gravitational and/or diapiric processes would predominate. However, this study shows pervasive tectonic deformation in the outer prism with coherent oblique shortening kinematics, which is achieved through an alternation of roughly N-S arcuate thrust systems connected by E-W transfer fault zones. These structures accord well with the geophysical models that propose westward rollback subduction. The main stage of tectonic activity occurred in the early-middle Miocene, but deformation lasted until the Quaternary with the same kinematics. Evaporite rocks played a leading role in the deformation as evidenced by the suite of ductile structures in gypsum distributed throughout the area. S- and L- gypsum tectonites, scaly clay fabrics, and brittle fabrics coexist and consistently indicate westward motion (top to 290°), with subordinate N-S contraction almost perpendicular to the transfer zones. This work reveals ductile tectonic fabrics in gypsum as a valuable tool to elucidate the structure and deformational history of complex tectonic mélanges involving evaporites above the décollement level of accretionary wedges.