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S. Mazzoli1,*A. Martín-Algarra2S.M. Reddy3V. López Sánchez-Vizcaíno4L. Fedele1 and A. Noviello1

  1. The evolution of the footwall to the Ronda subcontinental mantle peridotites: insights from the Nieves Unit (western Betic Cordillera)

  1. 1Department of Earth Sciences, University of Naples Federico II, Largo San Marcellino 10, 80138 Naples, Italy
  2. 2Departamento de Estratigrafía y Paleontología, Universidad de Granada, 18071 Granada, Spain 
  3. 3Institute for Geoscience Research & ARC COE for Core to Crust Fluid Systems, Department of Applied Geology, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia
  4. 4Departamento de Geología (Unidad Asociada al IACT-CSIC, Granada), Escuela Politécnica Superior de Linares, Universidad de Jaén, 23700 Linares, Spain
Journal of the Geological Society, London, Vol. 170, 2013, pp. 385–402. 
 

Abstract

F4.mediumStrongly heterogeneous deformation and extreme metamorphic gradients characterize the dominantly carbonate Nieves Unit in the footwall to the Ronda mantle extrusion wedge in the western Betic Cordillera. A well-developed foliation and mineral lineation, together with isoclinal intrafolial folds, occur in silicate-bearing, calcite or dolomite marbles within a c. 1.5 km thick metamorphic aureole underlying the peridotites. For the inferred maximum pressure of 300 MPa, petrological investigations allow us to define temperature ranges for the main zones of the metamorphic aureole: >510 °C (probably c. 700 °C) for the forsterite zone; 510–430 °C for the diopside zone; 430–360 °C for the tremolite zone; 360–330 °C for the phlogopite zone. Field structural analysis integrated with petrological, microstructural and electron backscatter diffraction textural data document large finite strains consistent with general shear within the metamorphic aureole, associated with NW-directed thrusting of the peridotites. On the other hand, post-kinematic silicate growth suggests that heat diffusion from the high-temperature peridotites continued after the final emplacement of the Ronda mantle extrusion wedge, leading to final zoning of the metamorphic aureole and to local partial annealing of calcite marble textures, particularly in the highest-temperature zone of the thermally softened footwall carbonates. Following substantial cooling, renewed crustal shortening affected the whole Nieves Unit, resulting in widespread development of NE–SW-trending meso-scale folds.