serie NOVA TERRA nº 49

38 The Cantabrian and South-Portuguese zones represent foreland (exter- nal) domains located at the Gondwanan and Laurussian fl anks of the orogen, respectively. The rest of the zones show variable intensity of metamorphism andmagmatismand thus make the hinterland (internal zone) of the orogen. More recently, Farias et al. (1987) de fi ned a new geotectonic zone within the hinterland of the Iberian Massif, the Galicia – Trás-os-Montes Zone, with far-travelled character and consti- tuted by a gigantic thrust-sheet overriding the Central Iberian Zone. This zone includes several allochthonous complexes which contain ophiolites and terranes recording high-P metamorphism, and are emplaced on top of a parautochthonous domain also termed Schistose Domain or Parautochthon ( Arenas et al., 1988 ). The Galicia – Trás-os- Montes Zone shows limited continuity, as it can only be followed in Galicia and along the Portuguese region of Trás-os-Montes, although a correlation of the nappe stack in the Ibero-Armorican arc across the Bay of Biscay has been recently proposed ( Ballèvre et al., 2014 ). Impor- tantly, this zone contains a Variscan suture, as suggested by the chronol- ogy of its ophiolites ( Díaz García et al., 1999; Sánchez Martínez et al., 2011; Arenas et al., 2014a ) and the high-P metamorphism experienced by some of its units ( Ordóñez Casado et al., 2001; Rodríguez et al., 2003; Fernández-Suárez et al., 2007; Abati et al., 2010 ). That suture zone is apparently rootless, as its trace lies above bedrock geology of Galicia to- wards the Atlantic Ocean to the West of the Malpica-Tui Complex ( Martínez Catalán et al., 2009 ). The aforementioned geotectonic division of the Iberian Massif is built on contrasted differentiation criteria from one region to the other, and so it suffers from signi fi cant divergences and inconsistencies. This is mainly due to the large amount of geologic data accumulated since the papers by Lotze (1945) and Julivert et al. (1972) were published. It is hence timely a revision of the subdivision that takes into account new advances in the geology of the Iberian Massif and that is based on uniform criteria. In this regard, perhaps the most important problems faced when subdividing the Iberian Massif concern the interpretation of the geology of its NW and SW sections. The SW Iberian Massif, speci fi cally the Ossa- Morena Zone, is characterized by lithological, structural and metamor- phic features that are also representative of the Galicia – Trás-os-Montes Zone ( Castro, 1987 ). For instance, the Ossa-Morena Zone contains ophiolites (e.g. Pedro et al., 2010 ), and units affected by high-Pmetamor- phism of Variscan age ( Azor et al., 1994; Ordóñez Casado, 1998; Moita et al., 2005; Pereira et al., 2010 ).These high-P units of SW Iberia have been recently correlated with equivalent units located in the NW of the Iberian Massif, allowing the proposal for a continuation of the rootless Variscan suture of NW Iberia and the allochthonous complexes of the same region to the W and SW ( Díez Fernández and Arenas, 2015 ). In this paper, we explore the existing geological data at the regional scale in order to review the subdivision of geotectonic zones of the Iberian Massif in an attempt to reach a simpler though successful scheme. We will mainly consider the new advances in the geology of NW and SW Iberia, speci fi cally the distribution of ophiolites and the units affected by high-P metamorphism together with the geochronology of these events, the interpretation of the autochthonous or allochthonous charac- ter of the main geological domains and the correlation along the Iberian Massif of all these fi rst order geological aspects. Our new approach allows a more integrative view of the geology of the Iberian Massif, which could be eventually considered for a simpler interpretation of the Variscan Orogen and the assembly of Pangea. The whole Variscan Orogen is affected by oroclinal bends, formed after an originally near-linear orogen ( Martínez Catalán, 2011; Weil et al., 2012 ). The Variscan Orogen can be followed from Iberia to the Bohemian Massif, forming also the basement of the Alps, Corsica and Sardinia. It has also continuity in Morocco and eastern North America in the Appalachian-Alleghanian Orogen and de fi nes a long collision zone generated during the main stages of Pangea's assembly ( Díez Fernández et al., 2012a; Arenas et al., 2014b ). Our aim is also to extrap- olate the new correlations proposed for Iberia throughout the Variscan Orogen, and to outline the distribution of the most internal zone of the orogen, the one featured by ophiolites and high-P units. Another consequence of the new correlations across the orogen is a better un- derstanding of the location of the true Rheic suture, which can be clearly distinguished now from other secondary sutures involved in the orogen ( Díez Fernández and Arenas, 2015 ). 2. The NW section of the Iberian Massif: the Galicia – Trás-os-Montes Zone The NW IberianMassif contains one of the most complete and repre- sentative sections of the Variscan Orogen. From East to West the North Iberia section extends from a foreland thrust and fold belt (Cantabrian Zone) through the external sectors of the hinterland represented by the West Asturian-Leonese and Central Iberian zones, and to the most internal domains well inside the hinterland (Galicia – Trás-os-Montes Zone) ( Fig. 1 ). The Galicia – Trás-os-Montes Zone includes the allochthonous com- plexes of the NW Iberian Massif, namely Cabo Ortegal, Órdenes, Mapica-Tui, Bragança and Morais complexes. They are preserved in late upright synforms and represent the remnants of a huge pile of far-travelled terranes, with different origin and tectonothermal evolu- tion. A detailed review of the geology of these allochthonous complexes has been presented by Arenas et al. (submitted for publication) . The upper and basal terranes have continental af fi nity and bear the imprint of two distinct high-P metamorphic events, whereas the intermediate terrane consists of a set of ophiolitic units ( Arenas et al., 2014b ) ( Fig. 1 ). They also include a thick serpentinitic mélange, the Somozas Mélange, only represented in the eastern part of the Cabo Ortegal Com- plex, i.e. at the advancing front of the allochthonous complexes ( Arenas et al., 2009 ). Therefore the allochthonous ensemble represents one of the sutures of the Variscan Orogen and contains key units to understand the earliest tectonothermal events related to the assembly of Pangea, and the origin of intervening oceanic domains. The allochthonous com- plexes are thrust on top of a parautochthonous domain, the so-called Schistose Domain of Galicia – Trás-os-Montes or Parautochthon ( Fig. 1 ). It is formed by Late Cambrian to Devonian metasedimentary rocks, Late Cambrian to Late Ordovician calc-alkaline and alkaline metavolcanics ( Valverde-Vaquero et al., 2005; Dias da Silva et al., 2014, in press ), and Upper Devonian to Early Carboniferous synorogenic sediments ( Martínez Catalán et al., 2016 ), all of which are tectonically emplaced onto the Central Iberian Zone. According to Piçarra et al. (2006) , stratigraphic and faunal af fi nities of the Silurian sediments of the Parautochthon suggest a more distal palaeogeographic position rel- ative to the Central Iberian Zone. Regarding the allochthonous com- plexes, the detrital zircon input from both the Parautochthon and the basal units of the allochthonous complexes are almost identical, so they are also considered as neighbouring sections of the same continen- tal margin ( Díez Fernández et al., 2012b ). The basal units are formed by metasedimentary rocks (comprising a pile of metagreywackes with alternations of metapelites, graphitic schists, calc-silicate rocks, metacherts and quartzites), calc-alkaline to peralkaline metagranitoids and more scarce ma fi c rocks. Maximum de- positional ages for themetasedimentary rocks range between Ediacaran and Early-Middle Cambrian ( Díez Fernández et al., 2010, 2013 ), while the granitic magmatism developed in the range c. 493 – 470 Ma, and was followed shortly after by alkaline – peralkaline magmatism ( Abati et al., 2010; Díez Fernández et al., 2012c ). The basal units have been interpreted as a section of the margin of Gondwana located between the West African Craton (WAC) and the Saharan Craton (SC) ( Díez Fernández et al., 2010 ). The fi rst Variscan tectonothermal event record- ed in these units is a high-P and low to intermediate-T (HP-LIT) meta- morphic event dated at c. 370 Ma ( Rodríguez et al., 2003; Abati et al., 2010 ). It was generated during oblique subduction of the Gondwana margin under a previously deformed ensemble (upper and ophiolitic units) located to the North (West in present-day coordinates; Díez Fernández et al., 2012a ). 136 R. Arenas et al. / Tectonophysics 681 (2016) 135 – 143