CADOMIAN SUBDUCTION COLLISION AND VARISCAN TRANSPRESSION IN THE BADAJOZ-CORDOBA SHEAR BELT, SOUTHWEST SPAIN

The tectonothermal evolution of the Badajoz-Cordoba shear belt (Southwest Iberian Massif, Spain) involved the build up of a Cadomian (Upper Proterozoic-Lower Paleozoic) subduction-collision orogenic wedge complex made up of five stacked tectonic slices, and its deformation under transpression during Hercynian (Late Paleozoic) intracontinental shearing episodes. Cadomian metamorphism in the high-grade gneissic units of the wedge complex is characterized by peak metamorphic conditions of almost-equal-to 720-degrees-C, 8 kbar, for the lowermost tectonic slice (Higuera de Llerena mylonite gneiss), and 670-degrees-C, 10 kbar, in the overlying gneissic slice (blastomylonitic migmatic gneisses). The P-T conditions recorded by eclogites structurally overlying the previous gneisses enhance a scheme of "inverted metamorphism", since these eclogites equilibrated at 685-700-degrees-C, > 15 kbar, during peak metamorphic conditions. After the high-pressure event, the highest temperatures attained by the eclogites correspond to a period of nearly isothermal decompression with a drastic decrease in pressure- Later on, the retrogressed eclogites experienced a pressure increase before they began to reequilibrate under progressively lower P and T conditions similar to those recorded by the retrogression of gneisses. Such a P increase in eclogites might be related to a period of underthrusting below continental crust responsible for the amalgamation of the different tectonic units of the Badajoz-Cordoba shear belt. The present results unravel that the models concerned with the geotectonic evolution of the lbero-armorican arc and the respective correlations among Hercynian and pre-Hercynian (Cadomian for our aims) terranes across the North Atlantic must be reconsidered.