Deciphering the tectono-metamorphic evolution of the Nevado-Filábride complex (Betic Cordillera, Spain) – A petrochronological study

Abstract

The Nevado-Filábride metamorphic complex (Betic Cordillera, Spain) exhibits a succession of Paleozoic and Mesozoic metasediments, orthogneisses and metabasites. The complex has been divided into three tectono-metamorphic units, from bottom to top: the Ragua, Calar-Alto and Bédar-Macael units. The petrochronological evolution of the complex is not well constrained as P-T-t conditions differ between authors mainly because of the investigated rock types and the thermobarometric and geochronological techniques applied. Five garnet-bearing mica-schists from various areas of the complex were investigated for constraining and comparing the shape of the P-T paths recorded by the three units. Quantitative compositional mapping of garnet and K-white mica was combined with iterative thermodynamic models. The resulting P-T trajectories suggest that the units experienced similar clockwise P-T trajectories during Alpine metamorphism. The three units reached high-pressure and low-temperature conditions of ~2.0 GPa and ~520 °C in the Bédar-Macael unit; ~2.0–2.2 GPa and ~470–490 °C in the Calar-Alto unit; and ~2.2 GPa and ~480 °C in the Ragua unit. All samples recorded a temperature increase of ~130 °C during exhumation as shown by the successive stages of white mica re-equilibrations. Heating during exhumation was probably triggered by the hot hanging wall over the Nevado-Filábride complex. The garnet rims reflect a high-temperature and low-pressure stage which was dated at ~13 Ma using allanite U-Th-Pb geochronology (LA-ICP-MS). Following the temperature peak, exhumation continued associated to cooling. Similarities in the shapes of P-T path throughout the units suggest a continuous metamorphic sequence rather a tectonically divided complex.