Forces controlling the intra-plate stress field: the Alboran Domain and the Eastern Pyrenees during the Miocene

Abstract

The Mediterranean region evolved due to different stages of extension caused by slab roll-back in a convergent regime imposed by the still continuing Africa-Eurasia convergence. The Betic-Gibraltar-Rif arc defines the rim of the Alboran Sea; the arc and sea together make up an example of such a zone of extension in a convergent regime. The westward migration of the Alboran Domain - caused by a combination of extensional collapse due to increased gravitational potential energy and slab roll-back induced by the retreating slab currently west of Gibraltar - influenced the area in several ways. The extensional collapse is responsible for the thrusting of the Alboran Domain on continental Iberia and the formation of the Betic-Gibraltar-Rif arc. The westward migration itself can be a cause for delaying the onset of the Messinian Salinity Crisis. Here, we focus on the question as to which first-order tectonic forces are influencing the Betic region and we will establish their relative importance. By looking at combinations of these tectonic forces with several finite element model runs, it can be shown that a combination of an Alboran Domain 'high' balanced with Africa-Eurasia convergence results in a zone with a neutral state of stress, vulnerable to westward roll-back related pull. A cessation of this pull can therefore be a direct cause for the closure of the Atlantic corridors due to the overtaking of compressional forces. The eastern Pyrenees are also vulnerable to this same compression. This area is of interest because the model is suitable for investigating the question if a combination of compression due to convergence and tension due to gravitational spreading forces can lead to an additional SW extensional phase. This second phase is presented in the field by Late Miocene extensional basins and volcanism.