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Tectonics of the Triassic rocks

Numerosos afloramientos de yesos del Triásico están implicados en una compleja tectónica en la Cordillera Bética. Muchos de estos afloramientos muestran rasgos característicos de zonas de cizalla. La complejidad de estos afloramientos ha llevado a pensar que podrían tratarse de depósitos olistostrómicos debido al gran desarrollo de megabrechas, cuando en realidad son brechas tectónicas que en numerosos casos constituyen una "mélange".

Tectonics, 36, 1006-1036 (2017)

An evaporite-bearing accretionary complex in the northern
front of the Betic-Rif orogen

Fernando Pérez-Valera, Mario Sánchez-Gómez, Alberto Pérez-López,
and Luis Alfonso Pérez-Valera


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.