Deciphering western Mediterranean kinematics using metamorphic porphyroblasts from the Alpujárride Complex (Betic Cordillera)

Abstract

3D microstructural analysis of porphyroblast inclusion trails using X-ray Computed Tomography is integrated with analysis of field structures to unravel the Alpine deformation history of the Alpujárride Complex, which constitutes the partially submerged metamorphic core of the Gibraltar Arc. Prograde metamorphism in the complex has been traditionally linked to a 'D1' event witnessed by inclusion trails in garnet porphyroblasts. Orientation data for these microstructures reveal three age groups with differently oriented axes of inclusion-trail curvature (known as FIA). The successive development of FIAs trending WNW-ESE, ENE-WSW and NNW-SSE is shown and correlated with the Paleogene-Neogene relative plate-motion paths of Africa, Iberia and the Alborán Domain as known from paleomagnetic data. During the late-metamorphic evolution of the Alpujárride Complex, after garnet growth had ceased, two steeply dipping crenulation cleavages and associated folds with roughly suborthogonal N–S and E-W trends developed, in addition to two subhorizontal ones. Inclusion trails are also found to exhibit a general preference for subvertical and subhorizontal orientations, suggesting a protracted orogenic evolution characterized by multiple stress permutations causing alternations of crustal shortening and gravitational collapse.