INVESTIGATING THE TECTONIC SIGNIFICANCE OF FOLIATION INTERSECTION AXES (FIA) WITHIN GARNET USING SM-ND GEOCHRONOLOGY

Foliation Intersection Axes (FIA) are microtectonic features preserved within rigid porphyroblasts that form during deformation. These features have been proposed to record an evolution of tectonic convergence vectors (i.e. the direction of maximum crustal shortening). Metamorphic terranes containing multiple FIA orientations could therefore record a region’s tectonic evolution. FIA are interpreted to form perpendicular to either: bulk shortening (assuming porphyroblastic non-rotation), or bulk shearing (assuming porphyroblastic rotation) directions; in either case FIA are interpreted to be important kinematic indictors. The Betic-Rif Cordillera is an arcuate fold and thrust belt orogen comprised of polydeformed, high-grade metamorphic complexes. Extensive structural research within the two stratigraphically deepest and most metamorphosed complexes in the Betic-Rif has found evidence for a complex deformation history that produced five successive sets of FIA, each with a distinctive and regionally consistent trend (Aerden et al., 2013; Ruiz-Fuentes and Aerden, 2018). These five FIA orientations apparently correlate with successive vectors of relative Africa-Iberia plate motion based on paleomagnetic studies (Rosenbaum et al., 2002). In this study we propose the use of Sm-Nd garnet geochronology on garnet porphyroblasts containing FIA orientations from two metamorphic complexes, the Nevado-Filabride Complex (SE Spain), and the overlying Sebtide Complex (NW Morocco) to determine whether this correlation is temporal as well as spatial. Garnet porphyroblasts collected from these complexes will be used to investigate the hypothesis that the preferred orientations of different FIA generations are preserving a record of plate motion of the African plate and Adrian microplate relative to the Iberian plate during the Mid-to Late Miocene. Preliminary Sm-Nd garnet ages on distinct garnet generations containing different FIA range from 35 to ~10 Ma, and generally correlate with the predicted FIA-age relationship across the region.