PRESSURE-TEMPERATURE-TIME-DEFORMATION EVOLUTION IN A NON-CYLINDRICAL OROGEN: THE BETIC-RIF CORDILLERA EXAMPLE (Invited Presentation)

The Mediterranean region and its orogens are characterized by complex geodynamic evolution through time. Several subduction zones, locally evolving in collision zones, are controlled by pre-orogenic inheritance including Mesozoic rifting events, nature and thermal age of the downgoing and overriding lithosphere and asthenospheric flow. Kinematic reconstructions of such complex orogens is the subject of active debates. Indeed, the evolution of the internal zones of these orogens are often non-consensual, especially their long-term Pressure-Temperature-time-deformation (P-T-t-d) histories. This problematic, linked to a complex shape of the Eurasian and African margins in pre-orogenic times and complex slab retreat and tearing dynamics, is particularly well illustrated in the Betic-Rif Cordillera, a strongly arcuated belt located in the westernmost part of the Mediterranean region.

Focusing on the Internal Zones of the Betic-Rif Cordillera and based on recent findings, a synthesis of the tectono-metamorphic evolution shows the relations in space and time between tectonic and P-T evolutions. In the western part of the belt, through a detailed field and structural study combined with a high-resolution map using RSCM geothermometry, the contact between the peridotite massifs and Mesozoic sediments has been reinterpreted as an extensional detachment, instead of a thrust as previously admitted. In the central and eastern parts of the chain, based on new ⁴⁰Ar/³⁹Ar ages in the Alpujárride Complex (metamorphic formations of the Betic Internal Zones) we conclude that the age of the HP-LT metamorphism is Eocene. A first-order observation is the contrast between the well-preserved Eocene HP-LT blueschists-facies rocks of the Central and Eastern Alpujárride Complex and the younger HT-LP conditions reaching partial melting recorded in the Western Alpujárride. Altogether these elements lead us to question the timing and mechanisms of mantle exhumation, the Mesozoic paleogeography, the pre-orogenic inheritance and the Cenozoic geodynamic evolution.

We propose a model where the large longitudinal variations in the P-T evolution are mainly due to (i) differences in the timing of subduction and exhumation from the Eocene, (ii) the nature of the subducting lithosphere and (iii) a major change in subduction dynamics at ~20 Ma associated with a slab-tearing event.