serie NOVA TERRA nº 49

42 the Central Iberian Zone, during a collision in Cadomian times (Late Proterozoic – Early Cambrian). The allochthonous complexes of NW Iberia would represent transitional parts between the Central Iberian and Ossa-Morena zones, but the Malpica-Tui Complex of NW Iberia and the Central Unit (Badajoz-Cordoba Corridor) were considered parts of a same lithological unit. Following Franke and Engel (1982) ; Castro (1987) also presented an updated geological map at the scale of the Variscan Orogen showing the location of the Rheic suture, described as the Hercynian suture. More recently, according to the presence of two high-P belts de fi n- ing its northern and southern limits, the Ossa-Morena Zone has been interpreted as part of an individual peri-Gondwanan continental micro- plate, drifted to some extent from the main continent. Such plate was identi fi ed as Armorica, a microcontinent that includes sectors of Iberia and Brittany ( Matte, 2001; Díaz-Azpiroz et al., 2006; Azor et al., 2008 ). The two high-P units would represent rooted sutures related to the dy- namics of Armorica and its Variscan accretion ( Simancas et al., 2001; Azor et al., 2008 ), but the real signi fi cance of the high-P units remain un- clear because an integrated model for their subduction and exhumation has not been presented so far. In the case of the Coimbra-Córdoba Shear Zone (Badajoz-Córdoba Corridor), it has also been proposed a Cadomian age for this suture ( Abalos et al., 1991 ). However, the lithologies and structural evolution as well as the age and type (HP-LIT) of metamorphism are similar in the basal allochtho- nous units of NW Iberian Massif and in the high-P units of the SW (Central Unit and Cubito-Moura Unit). Hence, these units can be corre- lated de fi ning a basal allochthonous terrane with continental af fi nity and structural continuity from NW to SW Iberia. Considering the high- P record of this terrane, the age of metamorphism (c. 370 Ma) and its structural position below ophiolitic units, this basal terrane has been identi fi ed as a subducted section of the Gondwanan margin and a mark- er of a long suture zone of Late Devonian age ( Fig. 1 ; Díez Fernández and Arenas, 2015 ). The ophiolitic units of the Ossa-Morena Zone are still poorly described although, regardless of their age, their structural position suggests a correlation with their structural equivalents in NW Iberia. One of the corollaries of the proposed correlation of both groups of allochthonous terranes in NW and SW Iberia is that the largest area of the Ossa-Morena Zone, the thick pile of metasedimentary and metaigneous rocks with Ediacaran-Devonian depositional/crystalliza- tion ages, rests on top of a group of units with clear allochthonous na- ture. The correlations established for the high-P units and the ophiolites, the general synformal structure of the Ossa-Morena Zone ( Borrego et al., 2005 ) and the activity of some signi fi cant faults, lead to an important conclusion: most of the central sector of the Ossa- Morena Zone is equivalent to the upper units of NW Iberia, thus representing a large allochthonous unit ( Fig. 1 ; Díez Fernández and Arenas, 2015 ). Accordingly, most of the Ossa-Morena Zone represents an allochthonous complex of the Iberian Massif, the Ossa-Morena Com- plex, which should be added to the Cabo Ortegal, Órdenes, Malpica-Tui, Bragança andMorais complexes. The rootless suture of NW Iberia can be therefore followed c. 1000 km south until the limit with the South Portuguese Zone, where the age of the Beja-Acebuches Ophiolite (340 – 332 Ma) clearly indicates that this is a much younger tectonic limit that transects all the previous nappes ( Fig. 1 ). This interpretation also allows to correlate pre-Variscan events in the upper units of NW Iberia ( Abati et al., 1999; Díaz García et al., 2010 ) and in the central part of the Ossa-Morena Zone (described as Cadomian), where its re- markable bearing has been widely accepted ( Galindo, 1989 ). Moreover, our proposal implies that some sectors usually included in the Ossa- Morena Zone represent the autochthonous domain of the new allochthonus complex. This is the case of the Sierra Albarrana Unit ( Azor, 1994; González del Tánago, 1995 ), and the entire structural domain resting below the Cubito-Moura Unit ( Fig. 1 ). According to the data and interpretations presented in previous sec- tions, the geology of NW and SW Iberian Massif can be described in terms of the presence of three different groups of allochthonous ter- ranes, the basal, ophiolitic and upper units ( Fig. 1 ). These terranes main- tain the same structural arrangement in both sectors of the Massif, and have comparable lithological constitution and tectonothermal evolu- tion. If this correlation holds correct, it should be accepted that the re- gions of the Iberian Massif where they appear must be interpreted similarly. However this is not the case so far because the structure of the Galicia – Trás-os-Montes Zone and the Ossa-Morena Zone has been interpreted in rather contrasted ways. Based on the structural and tectonostratigraphic correlation of both zones we propose their merging into a single geotectonic zone of the Iberian Massif: the Galicia – Ossa-Morena Zone ( Fig. 2 ). This new zone would be constituted by the allochthonous complexes of the Iberian Massif, from NE to SW, the Cabo Ortegal, Órdenes, Bragança, Morais, Malpica-Tui and Ossa- Morena complexes. The allochthonous complexes of the Galicia – Ossa-Morena-Zone are emplaced on top of a substrate that apparently shows some different characteristics in NW and SW Iberia. The Parautochthon of the NW sec- tion ( Fig. 2 ) does not seem to be represented in the SW, as comparable series have not been described so far. Moreover, sedimentary succes- sions such as the Serie Negra have not been found in the autochthonous sections of Central and NW Iberia, whereas it occurs in the autochtho- nous domains resting under the Ossa-Morena Complex de fi ned by Díez Fernández and Arenas (2015) . On the contrary, some of the metasedimentary series represented in the SW show great lithological similarities with the autochthonous sections of the Central Iberian Zone. In this regard, it is remarkable the presence of quartzitic facies, comparable to the Armorican Quartzite in fossil content and probable LLF OF AF HF CF DVC- GP MLF RF PRF VF ET NW IBERIA SW IBERIA OSSA-MORENA COMPLEX 0 50 km ÓRDENES COMPLEX MALPICA-TUI COMPLEX CABO ORTEGAL COMPLEX Rheic suture (reworked) SOUTH-PORTUGUESE ZONE GALICIA - OSSA-MORENA ZONE ALLOCHTHONOUS COMPLEXES PARAUTOCHTHON SW IBERIA AUTOCHTHON WESTASTURIAN-LEONESEZONE CANTABRIAN ZONE CENTRAL IBERIAN ZONE OSSA-MORENA COMPLEX Fig. 3. Composite cross-section showing the general structure of the Galicia – Ossa-Morena Zone and its relationships with the other geotectonic zones of the Iberian Massif. Based on the more detailed sections presented by Díez Fernández and Arenas (2015) . 140 R. Arenas et al. / Tectonophysics 681 (2016) 135 – 143