serie NOVA TERRA nº 49

134 ( Carvalhosa, 1999; Carvalhosa and Zbyszewski, 1994; Chichorro, 2006; Pereira et al., 2007 ). There are no isotopic age constrains for this upper sequence. However, a broad Cambrian-Ordovician age is considered the most probable age according to the regional setting ( Chichorro, 2006 ), although younger ages should not be discarded. Early Cambrian magmatism in this region is typically felsic, whereas Middle Cambrian – Ordovician magmatism is more ma fi c and with larger mantle contribu- tions ( Chichorro et al., 2008; Díez Fernández et al., 2015; Pereira et al., 2007; Sánchez-García et al., 2010 ). Culminating the regional structure, the Cabrela Unit consists of metasedimentary and metavolcanic rocks (mostly low-grade metamorphism) that rest discordantly over the crystalline basement described above (Carvalhal Unit), and account for a Lower Carbonifer- ous syn-orogenic marine basin ( Pereira and Oliveira, 2001, 2003; Z. Pereira et al., 2006; Pereira et al., 2012a, 2012b; Ribeiro, 1983 ). 2.2. NW Iberian massif 2.2.1. Regional structure The Variscan regional structure of NW Iberia is de fi ned by an autochthonous/parautochthonous domain overridden by a set of alloch- thonous terranes preserved as klippen ( Fig. 1 ; Martínez Catalán et al., 2007 ). Schists, gneisses andmigmatites of the autochthon/parautochthon are exposed along contiguous upright antiforms and domes separating the klippen ( Fig. 1 b). Initial Variscan deformation in the autochthonous/ parautochthonous domain developed mostly at medium-P conditions and was followed by low-P and high-T metamorphism and extensive Carboniferous magmatism ( Alcock et al., 2015; Arenas and Martínez Catalán, 2003; Escuder Viruete et al., 1997; Fernández-Suárez et al., 2000 ). The allochthonous terranes can be divided in three main counter- parts, from bottom to top: the basal, ophiolitic, and upper allochthonous units ( Arenas et al., 1986, 2016b; Martínez Catalán et al., 2009 ). The basal contacts of all these units are, originally, major thrusts, but many of them were reactivated and reworked as either secondary thrusts and/or later extensional shear zones ( Díez Fernández et al., 2013; Gómez Barreiro et al., 2010; Martínez Catalán et al., 2002, 2007 ). The basal allochthonous units consist of two dominantly terrigenous sequences ( Díez Fernández et al., 2010 ) affected by a high-P metamor- phic event (eclogite and blueschist facies conditions) dated at ca. 370 Ma (ca. 1.4 – 2.5 GPa; Abati et al., 2010; Arenas et al., 1995; Gil Ibarguchi and Ortega Gironés, 1985; López-Carmona et al., 2013, 2014; Rodríguez et al., 2003 ). The ophiolitic units are tectonic slices made of thick (from 300 m up to 4000 m) sequences of ma fi c rocks that may alternate with some metasedimentary rocks, layers of A B Alcáçovas Biscaia Safira Cabrela Montemor-o-Novo Silveiras Arraiolos Évora Valverde Boa Fé Cross-section 8º 15´ 38º 40´ N 0 3 km UPRIGHTANTIFORM UPRIGHT SYNFORM Low/Medium-grade domain (schists, gneisses, amphibolites) High-grade domain (gneisses and migmatites) Tonalites and granodiorites Grabbros and diorites VARISCAN MAGMATISM EDIACARAN AND CAMBRIAN (PRE-VARISCAN) SERIES Granites and granodiorites Porphyries (Beja Igneous Complex) South Portuguese Zone (Pulo do Lobo) EXT. DETACHMENT HIGH-ANGLE FAULT STRIKE-SLIP SHEAR ZONE Cabrela Fm; Toca de Moura volcanic-sedimentary complex VARISCAN SYN-OROGENICS Boa Fé shear zone Cabrela-Carvalhal synform Montemor-o-Novo antiform A B SW NE Porto-Tomar (subsidiary) shear zone FIG. 3 (a) (b) Fig. 2. (a) Simpli fi ed geological map and (b) NE – SW cross-section of the Évora Massif showing the two-layer crustal architecture and the main regional structures(after Carvalhosa et al., 1969, 1987; Carvalhosa and Zbyszewski, 1994; Carvalhosa, 1999; Pereira and Silva, 2002; Pereira et al., 2003, 2007, 2009 ). Location of Fig. 3 is indicated with a blue dashed line. (For interpretation of the references to colour in this fi gure legend, the reader is referred to the web version of this article.) 288 R.D. Fernández et al. / Lithos 268 – 271 (2017) 285 – 301