GEOCHRONOLOGICAL CONSTRAINTS ON THE EVOLUTION OF A SUTURE - THE OSSA-MORENA CENTRAL IBERIAN CONTACT (VARISCAN BELT, SOUTH-WEST IBERIAN PENINSULA)

One of the main tectonic boundaries of the Variscan Belt in the Iberian Peninsula is the Ossa-Morena/Central Iberian contact. This contact is marked by a highly deformed unit (Central Unit) which recorded an initial high-pressure/high-temperature metamorphic evolution. Rb-Sr whole-rock isotopic data from three gneissic bodies cropping out in the Central Unit yield two Late Proterozoic ages (690+/-134 and 632+/-103 Ma) and an early Palaeozoic age (495+/-13 Ma), which we interpret as protolith ages. The two Late Proterozoic orthogneisses show initial Sr-87/Sr-86 ratios typical of mantle-derived materials or those with significant mantle participation (Sr-87/Sr-86 > 0.709). These new radiometric data, together with ages previously published and the structural evolution of the Central Unit, lead to the conclusions that: (1) there are magmatic protoliths of Late Proterozoic and Early Palaeozoic ages; (2) the metamorphic evolution of this area, including the high-pressure event, belongs to the Variscan orogenic cycle; (3) the deformations observed affect the rocks of the entire Central Unit, accordingly they are post-Ordovician, i.e. Variscan; and (4) consequently, the Ossa-Morena/Central Iberian contact is interpreted here as a Variscan suture.