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

Abstract

We have investigated the stratigraphy, structure and metamorphism of the boundary 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 trending narrow band, namely, the Central Unit, in which partially retrogressed eclogites are included. During the Middle-Late Devonian the CIZ overthrust the OMZ, and in the footwall km-scale recumbent folds and thrusts developed 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 regime sank the overthrust block resulting in the exhumation of eclogites. These eclogites probably came from the underthrust OMZ lower crust, and they are at present included in the suture zone (Central Unit) of this continental collision. The extension is responsible for the origin of a basin and bimodal magmatism on the southern border of the CIZ. A late episode of folding and fracturing significantly contributed to the final complex picture of this suture boundary.