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Refined tectonic evolution of the Betic-Rif orogen through integrated 3-D microstructural analysis and Sm-Nd dating of garnet porphyroblasts
  • +3
  • Domingo Aerden,
  • Thomas P Farrell,
  • Ethan Baxter,
  • Emily Stewart,
  • Mohamed L. Bouybaouene,
  • Alejandro Ruiz Fuentes
Domingo Aerden
Universidad de Granada, Spain, Universidad de Granada, Spain, Universidad de Granada, Spain, Universidad de Granada, Spain, Universidad de Granada, Spain

Corresponding Author:[email protected]

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Thomas P Farrell
Boise State University,, Boise State University,, Boise State University,, Boise State University,, Boise State University,
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Ethan Baxter
Boston College, Boston College, Boston College, Boston College, Boston College
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Emily Stewart
Yale University, Yale University, Yale University, Yale University, Yale University
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Mohamed L. Bouybaouene
Département de Géologie, Université de Rabat, Département de Géologie, Université de Rabat, Département de Géologie, Université de Rabat, Département de Géologie, Université de Rabat, Département de Géologie, Université de Rabat
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Alejandro Ruiz Fuentes
Universidad de Granada, Universidad de Granada, Universidad de Granada, Universidad de Granada
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Abstract

High-resolution microstructural analysis of porphyroblast inclusion trails integrated with Sm-Nd garnet geochronology has provided new insight into the tectonic history of the Betic-Rif orogen. Three principal age groups of porphyroblast are demonstrated with distinctly oriented inclusion-trails. Inclusion-trail curvature axes or ‘FIA’ (Foliation Inflexion/Intersection Axes) are shown to represent ‘fossilized’ crenulation axes from which a succession of different crustal shortening directions can be deduced. The regional consistency of inclusion-trail orientations and their geometric relationship with several sets of macroscopic folds reveal the composite character of the Gibraltar Arc formed by a superposition of different folding directions and associated lineations. Bulk-garnet ages of 35-22Ma obtained from 5 micaschist samples of the Alpujarride-Sebtide complex (ASC) and of 35-13Ma from 4 micaschists of the Nevado-Filabride complex (NFC) allow to deduce NNE-SSW directed shortening in the Late Eocene changing to NW-SE shortening in the early Oligocene, alternating with suborthogonal NE-SW shortening during the Miocene. These directions can be related to a major swing in the direction of relative Africa-Iberia plate-motion known from kinematic modeling of magnetic seafloor anomalies, and dynamic interference between plate convergence and suborthogonal ‘tectonic escape’ of the Alboran Domain thereafter. Coupled to previously established P-T-t paths, the new garnet ages support a common tectono-metamorphic evolution of the ASC and NFC since the Late Eocene. However, while the first became exhumed in the Middle-Miocene (15Ma), the second experienced a re-subduction prior to being exhumed itself about 5 Myr later.