The geology of SW Iberia records a sequence of geologic events from the Cambrian-Early Ordovician rifting and subsequent passive margin development along the southern flank of the Rheic Ocean, to onset of oblique (sinistral) subduction in the Devonian, followed by oblique terrane accretion, ocean closure/continental collision and orogenic collapse. As a result, SW Iberia contains the southernmost exposure of the Pangean suture in the European Variscides. This suture zone is characterized by a belt of dismembered oceanic-related rocks and HP metamorphic complexes which are tectonically juxtaposed with the Gondwanan passive margin to the north (OMZ) and with the exotic South Portuguese Terrane to the south, which is thought to be either a remnant of Avalonia or Meguma.

Various segments of Variscan crust are currently exposed in Iberia in response to successive tectonic events during the Variscan orogeny itself and subsequent extensional and compressive events during the Alpine cycle, all accompanied by surface erosion, and collectively contributing to their exhumation. We review the main characteristics and geodynamic contexts of the metamorphic complexes developed in Iberia during the Variscan cycle, which include: (i) LP-HT complexes associated to the Cambrian-Early Ordovician rift stage; (ii) HP-LT complexes associated to subduction; and (iii) syn-to-post-collisional, MP and LP/HT complexes from the hinterland to the foreland fold-and thrust belts. All the above contexts are illustrated with case studies. Finally, a review of Variscan metamorphism in the Pyrenees and Catalan Coastal Ranges, located far away from the Rheic suture is also presented.

Synorogenic basins formed in all lithospheric units involved in the Variscan orogeny, i.e. the Gondwanan and Laurussian continental margins and also in the oceanic realm. However, examples of the latter are only preserved in SW Iberia. On the other hand, synorogenic deposits of the Gondwanan foreland are only preserved in NW Iberia, whereas remains of both continental margins exist in SW Iberia. Record of Variscan synorogenic basins also exists in basement exposures within the Alpine realm that occupies the eastern half of the Iberian Peninsula and the Balearic Islands. These, which are less known and in some cases of uncertain affinities, are described in a separate section.

A rifting stage initiated the Variscan cycle in NW Gondwana, lasted from Terreneuvian to Early Ordovician times and culminated in opening of the Rheic Ocean. The result of lithospheric stretching was the development of a horst-and-graben structure in the upper crust and formation of basins with sharp variations in thickness and facies of the sedimentary infill. Emplacement of large volumes of igneous rocks, both plutonic and volcanic, accompanied this stage in three different intervals: (i) Early Igneous Event (Terreneuvian), exclusively composed of felsic peraluminous rocks associated with the formation of core complexes in the mid-upper crust; (ii) Main Igneous Event (Cambrian Series 2 to Furongian), displaying bimodal character; and iii) Late Event (Tremadocian-Floian), with mixed characteristics of the other two events and abundant peralkaline rocks. The rifting axis was initially located close to the Cadomian suture that fringed the Ossa Morena Zone. For about 60 m.y. the rifting processes initially propagated "zip-like" along the axis and then widened cratonward to affect inner parts of Gondwana, such as the Central Iberian Zone. The rift/drift transition was diachronous, starting in Iberia (Ossa Morena Zone) in the Furongian.

The South Portuguese Terrane encompasses three major pre-orogenic mega-sequences: the Phyllite-Quartzite Group and the Tercenas Fm., the Volcanic-sedimentary Complex, and the Carrapateira Group, all three overlain by the syn-orogenic Baixo Alentejo Flysch Group, dealt with in Chap. 11. During the Mid-Late Devonian all the three mega-sequences belonged to an epicontinental sea. From the late Devonian to late Visean major changes took place: the region that became the IPB Domain was the locus of important lithospheric extension that led to the emplacement of important volumes of igneous rocks associated to a Volcanic-Sedimentary Complex, to which the VHMS ore deposits are associated; in Southwest Portugal the Tercenas Fm. shallow water sediments changed to a mixed-siliciclastic-carbonate shelf succession (Carrapateira Group); during the late Visean the extensional regime changed to crustal compression that caused the onset of huge deposits of flysch sediments (Baixo Alentejo Flysch Group) in successive depocenters migrating southward until the late Moscovian.

Progressive opening of the Rheic Ocean led to the drifting away of one or several ribbon terranes, generally ascribed to Avalonia, and inaugurated a passive margin stage on the newly formed margin of NW Gondwana. In Iberia, which remained on the Gondwanan side of the ocean, the rift to drift transition is recorded in the Ossa Morena Zone in latest Furongian times and migrated towards more internal parts of the margin during the Lower Ordovician. The passive margin stage is characterized by development of open marine platform sedimentation locally punctuated by eruption/intrusion of mainly basaltic, alkaline volcanic rocks, during transient periods of tectonic extension. A progression from outer (Ossa Morena Zone), through intermediate (Central Iberian and West Asturian-Leonese Zone, to inner (Cantabrian Zone) shelf environments can be generally established, although with significant variations related to local tectonic development. The end of the passive margin stage is marked by the formation of syn-orogenic basins, which roughly migrate in the same direction, i.e. from external to internal parts of the margin, as a response to the propagation towards the foreland of the Variscan orogenic wedge.

Finding of ca. 620Ma old zircons in a volcanic rock of the Loma del Aire unit, one of many structural divisions in the Ossa Morena Zone, some years ago, attracted much attention to this unit, which would contain, if proven, the oldest rocks so far dated not only in Ossa Morena but also in the entire Iberian Massif. In this paper, new field, petrographic, whole-rock geochemical and Sm–Nd isotope data as well as new TIMS U–Pb zircon ages are presented, which collectively allow a much better characterization and dating as Cambrian of the rock sequence in the Loma del Aire unit; the previously found ca. 620Ma old zircon population is now interpreted as xenocrysts incorporated in the Cambrian magma. Our data together with recently published provenance studies, bear important implications concerning the nature and evolution of the underlying lithospheric basement of the Ossa Morena Zone, which shares many characteristics with the Neoproterozoic peri-West-African craton arc systems currently exposed in the Precambrian inliers of the Moroccan Anti-Atlas, the North Armorican Zone of Brittany, Normandy and the Channel Islands (Cadomian Arc), and the Saxo-Thuringian and Teplá-Barrandian Zones of the Bohemian Massif. A correlation of the Ossa Morena zone with these arc systems in the Neoproterozoic and Early Paleozoic is thus proposed.

The Ossa Morena Zone of SW Iberia represents a continental arc accreted to the Iberian Autochthon during the Late Proterozoic-Early Cambrian Cadomian orogeny. A subsequent Cambrian-Ordovician rifting event is recorded in this zone, which was accompanied by intrusion/eruption of large volumes of igneous rocks. Exposed crustal segments show both volcanic and shallow plutonic rocks that according to their relationship with coeval sedimentary successions can be assigned to one of two periods of magma emplacement: i) an Early Igneous Event, exclusively comprised of acid peraluminous rocks associated with migmatite formation during development of core-complex structures in mid-upper crust environments; and ii) a Main Igneous Event, which produced predominantly basaltic and acid (rhyolite) rocks and minor amounts of intermediate (trachyte) rocks. Tholeiites and alkaline rocks predominate in this suite but minor calcalkaline peraluminous compositions are also present. Besides, a volumetrically unimportant but petrologically significant group of Mg-rich rocks also occurs within the Main Igneous Event. These latter rocks are interpreted to reflect high partial melting rates of a protolith similar to the primitive mantle. All the outlined characteristics provide evidence for large heterogeneity within the rift-related association that may be due to several causes, such as the involvement of various magma sources (asthenospheric, lithospheric, crustal) and/or involvement of various petrogenetic processes in their generation and evolution.Radiometric (U-Pb zircon) dating yielded c. 530 +/- 5 Ma ages for the Early Igneous Event and a longer duration, 517-502 +/- 2 Ma, for the Main Igneous Event.The large volume of magma emplaced into upper crustal environments, along with the presence of abundant dikes, suggest that magma ascent benefited from coeval extensional tectonism. It is suggested that they represent the igneous expression of rifting in connection with a severe thermal modification of the lithosphere, probably caused by an underlying thermal anomaly. A model is presented that considers a ridge/trench collision process as the triggering motor of the described evolution, which culminated in the opening of the Rheic Ocean in Early Ordovician time. (C) 2008 Elsevier B.V. All rights reserved.

New U–Pb zircon ages from the Santa Olalla Igneous Complex have been obtained, which improve the knowledge of the precise timing of Variscan magmatism in the Ossa–Morena Zone, SW Iberia. This complex has a special relevance as it hosts the most important Ni–Cu–platinum group element (PGE) mineralization in Europe: the Aguablanca deposit. U–Pb zircon ages have been obtained for seven samples belonging to the Santa Olalla Igneous Complex and spatially related granites. With the exception of the Cala granite (352 ± 4 Ma), which represents an older intrusion, the bulk of samples yield ages that cluster around 340 ± 3 Ma: the Santa Olalla tonalite (341.5 ± 3 Ma), the Sultana hornblende tonalite (341 ± 3 Ma), a mingling area at the contact between the Aguablanca and Santa Olalla stocks (341 ± 1.5 Ma), the Garrote granite (339 ± 3 Ma), the Teuler granite (338 ± 2 Ma), and dioritic dykes from the Aguablanca stock (338.6 ± 0.8 Ma). The Bodonal–Cala porphyry, which has also been dated (530 ± 3 Ma), comprises a group of sub-volcanic rhyolitic intrusions belonging to the Bodonal–Cala volcano-sedimentary complex, which hosts the igneous rocks. The knowledge that emplacement of the Aguablanca deposit was related to episodic transtensional tectonic stages during the Variscan orogeny will be fundamental in future mineral exploration in the Ossa–Morena Zone.

The Santa Olalla Igneous Complex, a late-Variscan group of intrusions located in the Ossa-Morena Zone (SW Iberia), has been the focus of a gravity and structural study. The structure outlined by the foliation map is complex, showing two different structural domains: one characterized by vertical, and the other by horizontal, magmatic foliations. The vertical fabrics are restricted to the NE half of the complex, which is in direct contact with a Variscan sinistral strike-slip fault (Cherneca fault) whereas the horizontal fabrics are developed in the SW half of the complex, which is characterized by a horizontal tabular geometry. Gravity modeling indicates that the deeper floor of the plutons is closely related to the NE margin and the Cherneca fault. An emplacement and structural evolution model for this igneous complex is proposed following these structural and gravity results: (1) magma ascent was favored by releasing bends in the trace of the Cherneca fault; (2) when magma reached the present level it intruded to the SW with a horizontal sheet geometry generating the subhorizontal foliation domain; (3) after emplacement, the NE half of the complex suffered the external tectonic stress field provoked by sinistral motion along the Cherneca fault, subsequently generating the subvertical magmatic foliation domain.

The Rheic Ocean is widely believed to have formed in the Late Cambrian-Early Ordovician as a result of the drift of peri-Gondwanan terranes, such as Avalonia and Carolina, from the northern margin of Gondwana, and to have been consumed in the Devonian Carboniferous by continent-continent collision during the formation of Pangea. Other peri-Gondwanan terranes (e.g., Armorica, Ossa-Morena, northwest Iberia, Saxo-Thuringia, Moldanubia) remained along the Gondwanan margin at the time of Rheic Ocean formation. Differences in the Neoproterozoic histories of these peri-Gondwanan terranes suggest the location of the Rheic Ocean rift may have been inherited from Neoproterozoic lithospheric structures formed by the accretion and dispersal of peri-Gondwanan terranes along the northern Gondwanan margin prior to Rheic Ocean opening.Avalonia and Carolina have Sm-Nd isotopic characteristics indicative of recycling of a juvenile ca. 1 Ga source, and they were accreted to the northern Gondwanan margin prior to voluminous late Neoproterozoic arc magmatism. In contrast, Sm-Nd isotopic characteristics of most other peri-Gondwanan terranes closely match those of Eburnian basement, suggesting they reflect recycling of ancient (2 Ga) West African crust. The basements of terranes initially rifted from Gondwana to form the Rheic Ocean were those that had previously accreted during Neoproterozoic orogenesis, suggesting the rift was located near the suture between the accreted terranes and cratonic northern Gondwana. Opening of the Rheic Ocean coincided with the onset of subduction beneath the Laurentian margin in its predecessor, the Iapetus Ocean, suggesting geodynamic linkages between the destruction of the Iapetus Ocean and the creation of the Rheic Ocean.

The western part of the Iberian Peninsula (Iberian Massif) is the best exposed fragment of the Variscan orogen in Europe. Its southern half was generated by an oblique collision between three continental terranes belonging to the margins of Laurassia (Avalonia) – the South Portuguese Zone (SPZ) – and Gondwana – the Ossa Morena Zone (OMZ) and the Central Iberian Zone (CIZ). The boundaries between them are considered to be suture zones. A 200 km long magnetotelluric profile across the three Variscan terranes was done in a NNE direction, approximately perpendicular to the main tectonic features. The results of two-dimensional inversion of the MT dataset reveal high-conductivity zones coinciding with the transitions SPZ/OMZ and OMZ/CIZ. These conductive bodies related to the sutures at depth were interpreted as graphite enrichments along shear planes formed due to the overall transpressive regime. A high-conductivity layer extending along the whole OMZ was found at a depth of 15–25 km, the top of which spatially correlates with a broad reflector detected by a recently acquired deep seismic reflection profile. The high conductivity was interpreted as caused by the Precambrian Serie Negra graphite-rich rocks. Carbon and oxygen X-ray mapping with electron microprobe on polished sections of Serie Negra samples from OMZ revealed the presence of interconnected graphite, which supports the hypothesis that graphite is determinant for the high conductivity. Two graphite types, which help to record the geological evolution, were identified: graphite accumulations in the schistosity surfaces produced by folding and metamorphism, and metallic films of graphite developed along late faults. The conductive layer shows blobs of higher conductivity suggesting macro-anisotropy. Additional mylonitisation and shearing produced by thrusting at depth can be the origin of these zones of enhanced conductivity, given that the detachment level is located within the Serie Negra. Several high-resistivity features were found in the upper crust, related to Devonian and Carboniferous successions and probably to some unexposed plutons in the SPZ and the Palaeozoic series of OMZ plus some granitic intrusions. In the CIZ, a high-resistivity zone extending to the whole crust is correlated with extensive late Variscan granite intrusions.

An important rifting event, accompanied by massive igneous activity, is recorded in the Ossa-Morena Zone of the SW Iberian Massif (European Variscan Orogen). It likely culminated in the formation of a new oceanic basin (Rheic ocean?), remnants of which appear presently accreted at the southern margin of the Ossa-Morena Zone. Rifting propagated diachronously across the zone from the Early Cambrian to the Late Ordovician, but by Early Ordovician time, the existence of a significant tract of new ocean is evidenced by a breakup unconformity. Although early stages of rifting were not accompanied by mantle-derived igneous activity, a pronounced increase of the geothermal gradient is indicated by partial melting of metasedimentary protoliths in the upper and middle crust, and by coeval core-complex formation. Geochemistry of the main volume of igneous rocks, emplaced some million years later during more mature stages of rifting, suggests an origin in a variably enriched asthenospheric source, similar to that of many OIB, from which subsequent petrogenetic processes produced a wide range of compositions, from basalt to rhyolite. A tectonic model involving collision with, and subsequent overriding of, a MOR is proposed to account for the overall evolution, a present-day analogue for which lies in the overriding of the East Pacific Rise by North America and the rifting of Baja California.

The Geosites Project, initiated by the IUGS Global Geosites Working Group and supported by UNESCO, aims to produce a global inventory of the Earth's geo- logical heritage. This global inventory requires a sys- tematic methodology, based on the selection of geologi- cal frameworks of international significance in each country. These frameworks are topic events, temporal or regional geotectonic elements, etc. The second step of this methodology is the selection of the most valuable and representative sites of these geological frameworks (geosites). Fortunately, the geological diversity of Spain provides a great number of frameworks of global signif- icance. In addition, the high quality of the outcrops (for topographic and climatic reasons) will allow for the selection of illustrative geosites. This paper presents a list of Spanish geological frameworks drawn up by con- sensus. It was prepared in accordance with the Geosites Project methodology, without taking into account the National Inventory of Geosites, which is in progress and covers 40% of Spanish territory. The IGME (Geological Survey of Spain) drew up a preliminary list, which was sent to all the university departments of geology, mining schools and research centres, for analysis, discussion and improvement. The result of this request was the selection of 20 frameworks, forming the first Spanish contribution to the Geosites Project.