Abstract Field relationships and new U–Pb geochronology data indicate a temporal link between the diverse high-K mafic–intermediate magmas of the Ossa–Morena Zone (OMZ). Ages of c. 338–335 Ma for the Vale de Maceiras gabbro and the Campo Maior microdiorite and quartz-diorite indicate that plutonism took place during a Variscan extensional D 2 deformation event in the OMZ. The syntectonic nature of the Vale de Maceiras pluton is attested to by the orientation of intrusive contacts, magmatic foliation and the growth of contact metamorphic minerals in relation to the Variscan extensional D 2 foliation. The Campo Maior microdiorite, quartz-diorite and orthomigmatites are temporally linked to high-temperature mylonitic gneisses formed simultaneously with the Variscan extensional D 2 deformation event. The geochemical features of the Vale de Maceiras and Campo Maior mafic–intermediate rocks show an affinity with the sanukitoid series. This finding suggests that the observed geochemical variability, from tholeiitic to calc-alkaline and sanukitoid, in the Visean OMZ plutonic rocks ( c. 349–335 Ma) may have been inherited from partially melted mantle domains that were previously contaminated by crustal melts during subduction.

Abstract New laboratory experiments using granulite xenoliths support a dual origin for I-type granites as primary and secondary. Primary I-type granites represent fractionated liquids from intermediate magma systems of broadly andesitic composition. Fluid-fluxed melting of igneous rocks that resided in the continental crust generates secondary I-type granites. The former are directly related to subduction, with Cordilleran batholiths as the most characteristic examples. Experiments with lower crust granulite sources, in the presence of water, show that amphibole is formed by a water-fluxed peritectic rehydration melting reaction . Entrainment of only 10% of restites composed of amphibole, pyroxene, plagioclase and magnetite, is sufficient to account for discrepancies in aluminium saturation index and maficity in secondary I-type granites. Lower crust granulite xenoliths, attached to a sanukitoid containing 6 wt% water, have been used in two-layer capsules to test fluid-fluxed melting reactions as the origin of secondary I-type granites. It is proposed that sanukitoid magmas act as water donors that trigger extensive melting of the lower crust, giving rise to granodioritic liquids. Because primary granites are related to coeval subduction, and secondary ones are crustal melts from older subduction-related rocks, the distinction between both I-types is essential in tectonic reconstructions of ancient orogenic belts.

Abstract Following a Middle–Late Devonian ( c . 390–360 Ma) phase of crustal shortening and mountain building, continental extension and onset of high-medium-grade metamorphic terrains occurred in the SW Iberian Massif during the Visean ( c . 345–326 Ma). The Évora–Aracena–Lora del Rı́o metamorphic belt extends along the Ossa–Morena Zone southern margin from south Portugal through the south of Spain, a distance of 250 km. This major structural domain is characterized by local development of high-temperature–low-pressure metamorphism ( c . 345–335 Ma) that reached high amphibolite to granulite facies. These high-medium-grade metamorphic terrains consist of strongly sheared Ediacaran and Cambrian–early Ordovician ( c . 600–480 Ma) protoliths. The dominant structure is a widespread steeply-dipping foliation with a gently-plunging stretching lineation generally oriented parallel to the fold axes. Despite of the wrench nature of this collisional orogen, kinematic indicators of left-lateral shearing are locally compatible with an oblique component of extension. These extensional transcurrent movements associated with pervasive mylonitic foliation ( c . 345–335 Ma) explain the exhumation of scarce occurrences of eclogites ( c . 370 Ma). Mafic-intermediate plutonic and hypabyssal rocks ( c . 355–320 Ma), mainly I-type high-K calc-alkaline diorites, tonalites, granodiorites, gabbros and peraluminous biotite granites, are associated with these metamorphic terrains. Volcanic rocks of the same chemical composition and age are preserved in Tournaisian–Visean ( c . 350–335 Ma) marine basins dominated by detrital sequences with local development of syn-sedimentary gravitational collapse structures. This study, supported by new U–Pb zircon dating, demonstrates the importance of intra-orogenic transtension in the Gondwana margin during the Early Carboniferous when the Rheic ocean between Laurussia and Gondwana closed, forming the Appalachian and Variscan mountains.

Abstract Most Palaeozoic magmatic rocks in Spain were produced during the Variscan orogeny, and there are excellent and abundant examples of both volcanic and plutonic lithologies. Volcanic units include those in the world-famous Iberian Pyrite Belt, and plutonic rocks exposed in the Iberian Massif include some of the largest and best granite outcrops in the European Variscides. Magmatic rocks are present in all the Iberian tectonostratigraphic zones into which the Variscan orogen in Spain has been classically divided. In addition to these Variscan igneous rocks, there is also evidence for earlier magmatism, including widespread exposures of Neo-proterozoic–Cambrian (Cadomian) age, and the diatreme-like breccias linked to the origin of the remarkable mercury mineralization at Almaden. In this chapter we deal initially with Palaeozoic volcanic rocks, with special emphasis on the volcanism related to the generation of the Iberian Pyrite Belt. With regard to the Variscan granitoid rocks we have grouped these according to compositional features and relative age, rather than by tectonostratigraphic zones (the latter approach does not contribute to a better understanding of the magmatism because the emphasis is on differences and not on similarities). However, Variscan granites of the Iberian Massif are described separately from other granitic massifs in the Pyrenees and Catalonian Coastal ranges, because of their geographic separation and the lack of obvious direct links between them. Outcrops of distinctive mafic and ultramafic rocks, mostly related to granitoids of the appinite–granodiorite association (cf. Pitcher 1997 ), are treated separately, not least because of their importance in international

Abstract Granite magmatism represents a major contribution to crustal growth and recycling and, consequently, is one of the most important mechanisms to have contributed to the geochemical differentiation of the Earth’s crust since the Archaean times. The important role of granites has been acknowledged from the times of James Hutton, being an important part of Hutton’s (1785) work The Theory of the Earth . Since that time, advances in Earth Sciences and the development of analytical instruments have produced a vast amount of data from granite terrains around the world (see, for instance, the Proceedings of the Hutton symposia , 1988, 1992, 1996). However, many problems still remain unsolved. There have been several important controversies concerning granites during the last 50 years. One of the best remembered was that led by H. H. Read and N. L. Bowen around the 1950s (Read 1958). The end of this obscure controversy, full of misunderstandings and with some rhetoric, ended with the publication of the classic memoir by O. F. Tuttle & N. L. Bowen (1958) entitled Origin of granites in the light of experimental studies in the system NaAlSi 3 O 8 -KAlSi 3 O 8 -SiO 2 -H 2 O . The main conclusion of this study was that granitic liquids may be generated from melting of quartzo-feldspathic rocks in excess water, at depths of ‘… 12–21 km in geosynclinal areas where the initial gradient is on the order of 30°C/km’ (Tuttle & Bowen 1958, p. 2). Detailed phase relationships in the granite system were determined in this seminal work. However, the conditions for the generation of granite