New lithostratigraphic and tectonic data on the southern border of the Central-Iberian Zone (Portugal)

Abstract

The geological cartography review of the Portalegre-Serra de S. Mamede region recognized a lithostratigraphic succession from the neoproterozoic to lower carbonic, with similar characteristics to the Amêndoa-Carvoeiro synform. The differences between the two successions occur at the top and near the bottom; lower Carboniferous units (Visean) and in the absence of the Vale do Grou Group (Upper Cambrian?) were identified in the S. Mamede synform. The works carried out showed tectonic transition from flattening regime by pure shear in the axial zone of the ZOM and in the ZOM / ZCI limit to pass an oblique shear marked by thrust with top to NE associated with left movement already in the ZCI (Portalegre). Further into the ZCI the flattening regime is pure (S. Mamede). In the central part of the S. Mamede synform was identified by thrust-sheet, designated by Soverete and Montarecos, both characterized by the transport of metasediments to NE and generated in the early episodes of the D1 varican phase. The first, it places meta-sediments, locally with Upper Ordovician fossils, on quartzites strata of the lower Devonian, while another is responsible for the transport of Siluric schist lithologies, sometimes carbonaceous, in the quartzites. The structural data obtained resulted of the deformation events in the Variscan orogenic phase, taking into account the flower structure model already pointed out for this region.