The structure of a major suture zone in the SW Iberian Massif: the Ossa-Morena/Central Iberian contact

We have investigated the stratigraphy, structure and metamorphism of the bo undary between the Ossa Morena Zone (OMZ) and the Central Iberian Zone (CIZ ), two significant continental portions of the Variscan Iberian Massif. The OMZ/CIZ contact is marked by a strongly deformed and metamorphosed NW-SE t rending narrow band, namely, the Central Unit, in which partially retrogres sed eclogites are included. During the Middle-Late Devonian the CIZ overthr ust the OMZ, and in the footwall km-scale recumbent folds and thrusts devel oped with decoupling and underplating of the lower crust. At the same time, in the hanging wall there took place intense though localized back-folding and back-shearing. In the Early Carboniferous a transtensional tectonic re gime sank the overthrust block resulting in the exhumation of eclogites. Th ese eclogites probably came from the underthrust OMZ lower crust, and they are at present included in the suture zone (Central Unit) of this continent al collision. The extension is responsible for the origin of a basin and bi modal magmatism on the southern border of the CIZ. A late episode of foldin g and fracturing significantly contributed to the final complex picture of this suture boundary. (C) 2001 Elsevier Science B.V. All rights reserved.