Abstract
The modes in which the lithosphere deforms during continental collision and the mechanisms involved are not well understood. While continental subduction and mantle delamination are often invoked in tectonophysical studies, these processes are difficult to be confirmed in more complex tectonic regions such as the Gibraltar Arc. We study the present‐day density and compositional structure of the lithosphere along a transect running from South Iberia to North Africa crossing the western Gibraltar Arc. This region is located in the westernmost continental segment of the African‐Eurasian plates, characterized by a diffuse transpressive plate boundary. An integrated and self‐consistent geophysical‐petrological methodology is used to model the lithosphere structure variations and the thermophysical properties of the upper mantle. The crustal structure is mainly constrained by seismic experiments and geological data, whereas the composition of the lithospheric mantle is constrained by xenolith data. The results show large lateral variations in the topography of the lithosphere‐asthenosphere boundary. We distinguish different chemical lithospheric mantle domains that reproduce the main trends of the geophysical observables and the modeled P and S wave seismic velocities. A sublithospheric body colder than the surrounding mantle is needed beneath the Betics‐Rif to adjust the measured potential fields. We link this body to the Iberian slab localized just to the east of the profile and having some effect on the geoid and Bouguer anomalies. Local isostasy allows explaining most of the topography, but an elastic thickness higher than 10 km is needed to explain local misfits between the Atlas and the Rif Mountains.
Highlights
The target area of this study is located in the westernmost segment of the African‐Eurasia continental plate boundary, in the transition from the western Mediterranean to the Atlantic Ocean (Figure 1)
The Betics and Rif orogens are depicted as thin skinned along the geotransect whereas the Atlas Mountains are interpreted as thick skinned by the product of basin inversion during the Cenozoic
The crust underneath the Hercynian Iberian Massif is about 32 km thick, whereas the crust beneath the Anti‐Atlas is slightly thicker reaching 35 km of thickness
Summary
The target area of this study is located in the westernmost segment of the African‐Eurasia continental plate boundary, in the transition from the western Mediterranean to the Atlantic Ocean (Figure 1). The protracted convergence between the African and European plates accommodates over a widespread tectonically active deformation zone comprising the southern Iberian Massif, the Betic‐Rif arcuate orogen with its associated Alboran back‐arc basin and Guadalquivir and Rharb foreland basins, and the intracontinental Atlas Mountains. The entire region is affected by shallow, intermediate, and even deep seismicity showing normal, inverse, and strike‐slip focal mechanisms with hypocenter clustering related to major tectonic structures (e.g., Buforn et al, 2016; Custódio et al, 2016). There is a widespread volcanism over the study region affecting central Iberia and its eastern margin, the Alboran basin, and the Atlas Mountains (Figure 1). In addition to the Cenozoic volcanism in North Africa, the volcanic activity has concentrated during the mid and late Miocene and Pliocene to Recent showing orogenic and anorogenic affinities (e.g., Duggen et al, 2005; Lustrino et al, 2011; Lustrino & Wilson, 2007; Melchiorre et al, 2017)
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