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 Iberia n Peninsula is the Ossa-Morena/Central Iberian contact. This contact i s marked by a highly deformed unit (Central Unit) which recorded an in itial high-pressure/high-temperature metamorphic evolution. Rb-Sr whol e-rock isotopic data from three gneissic bodies cropping out in the Ce ntral Unit yield two Late Proterozoic ages (690+/-134 and 632+/-103 Ma ) and an early Palaeozoic age (495+/-13 Ma), which we interpret as pro tolith ages. The two Late Proterozoic orthogneisses show initial Sr-87 /Sr-86 ratios typical of mantle-derived materials or those with signif icant mantle participation (Sr-87/Sr-86 > 0.709). These new radiometri c data, together with ages previously published and the structural evo lution of the Central Unit, lead to the conclusions that: (1) there ar e 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 o bserved affect the rocks of the entire Central Unit, accordingly they are post-Ordovician, i.e. Variscan; and (4) consequently, the Ossa-Mor ena/Central Iberian contact is interpreted here as a Variscan suture.