The Ronda peridotites (Los Reales nappe): An example of the relationship between lithospheric thickening by oblique tectonics and late extensional deformation within the Betic Cordillera (Spain)

Abstract

The Internal (or metamorphic) Zone of the Betic Cordillera (southern Spain) is a 400 km long and ENE-elongated tectonic domain characterized by a widespread record of alternating compressional and extensional processes. In the westernmost part of the Internal Zone several orogenic Iherzolite massifs—the Ronda peridotites—were also involved in such processes. The Ronda peridotites form the lower portion of the Los Reales nappe and are overlain by a metamorphic sequence which varies from granulite- to greenschist-facies conditions. The tectono-metamorphic history of the Los Reales nappe involves two main synmetamorphic steps. A first extensional event at lithospheric scale is preserved within the attenuated continental crust which overlies the Ronda peridotites. It was related to the upwelling of an asthenospheric diapir below the thinned lithosphere, and led to the development of low-pressure-high-temperature metamorphism and of ductile shear zones with N110°E-trending stretching lineations. A subsequent compressional event is represented by the hot thrusting of the Ronda peridotites from the west-southwest to the east-northeast. Finally, late extensional deformations in a dominant N-S direction developed in response to the lithospheric thickening achieved during the former compressional event. The kinematics of the synmetamorphic deformations can be integrated into a model of sinistrally oblique tectonics compatible with the overall strike-slip motion of the African and Iberian plates from Jurassic to Tertiary times, whereas the later deformations should reflect the convergence between Africa and Iberia from Tertiary time onwards.