Wrenching in the external zone of the Betic Cordilleras, southern Spain

Abstract

Regional structural trends in the Caravaca-Huescar area, forming the central part of the External Zone in the Betic Cordilleras, indicate that deformation of the area results from right lateral wrenching, subparallel to the paleogeographic zonation. The structural trends do not fit the nappe interpretation generally used elsewhere in the External Zone. Arguments for wrenching in the area are: the structural inverse symmetry with respect to a central transcurrent fault zone (the Crevillente Fault Zone), the distributional pattern of stratigraphic anomalies and types of deformation, and the outcrop pattern of the paleogeographic zones. It is argued that certain tectonic units in the area, formerly interpreted as klippes in a nappe configuration, form centers of “flower structures” and are vertically squeezed out blocks. A theoretical model is sketched, illustrating the evolution of a wrench zone under the stratigraphic conditions of the studied area and resulting in its present characteristics. Many of the features of the Caravaca-Huescar area are also present elsewhere in the External Zone and support the idea that wrenching was a major deformational mechanism. It is therefore suggested that the External Zone should in general not be described in terms of a nappe structure, as has been done so far, but in terms of a strike-slip orogen or a wrenched continental margin.