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This work assessed the age distribution of Cadomian/Pan-African orogenic events (550-590 and 605-790Ma, respectively) in several zones of Iberian Massif by means of detrital and inherited zircon analysis compilation. Detrital zircon age spectra show that throughout the late Neoproterozoic-to-Early Ordovician era (~120Ma sedimentary record), the main systematic peak occurs at ~610Ma, followed by peaks at typical Cadomian ages (~590-550Ma). Inherited zircons incorporated in Cambrian-to-Lower Ordovician igneous rocks show typical Cadomian ages (~590-550Ma) but, once again, a remarkably consistent Pan-African ~610Ma peak occurs. In accordance with compiled zircon data and taking into account the evidence of North African peri-cratonic inliers, Ediacaran (~610Ma) zircons incorporated in Paleozoic magmas provide indirect evidence of Pan-African magmatism, suggesting that these magmas and synorogenic sediments are likely to constitute the cryptic stratigraphic infrastructure of most of the Iberian Massif. The main source of ~610Ma inherited zircons may be the lateral chrono-equivalents of the Saghro and Bou Salda-M-Gouna Groups (Anti-Atlas, Morocco) and/or coeval igneous rocks from West African Craton or Trans-Sahara Belt, emplaced at a stratigraphic level below the late-Ediacaran sediments of the Ossa Morena Zone and the Central Iberian Zone. Assuming that the Iberian crust is a fragment of the Pan-African orogen, a relative paleoposition situated between the West African Craton and the Trans-Saharan Belt during the Late Neoproterozoic is proposed. The closedsystem behaviour of Stenian-Tonian detrital zircon ages in the Trans-Sahara Belt suggests that this mega-cordillera acted as a barrier, in paleogeographic terms, separating the Sahara Metacraton from Iberia. In Iberia, the opening of the system to Stenian-Tonian detrital zircons during the Ordovician indicates that, at that time, the Trans-Saharan Belt had already become a vast peneplain, which favoured a large drainage system with a long-distance transport mechanism that fed the passive continental margins. [ABSTRACT FROM AUTHOR]

Carboniferous magmatism in southwestern Iberia was continuously active for more than 60 m.y. during the development of the Appalachian-Variscan belt of North America, North Africa and Western-Central Europe. This collisional orogen that records the closure of the Rheic Ocean is essential to understanding the late Paleozoic amalgamation of the Pangea supercontinent. However, the oblique convergence between Laurussia and Gondwana that lasted from the Devonian to the Carboniferous was likely more complex. Recently, a new tectonic model has regarded the Iberia Variscan belt as the site of coeval collisional and accretionary orogenic processes. Early Carboniferous plutonic rocks of southwest Iberia indicate arc magmatism in Gondwana. The Ossa-Morena Zone (OMZ) acted as the upper plate in relation to the geometry of the Paleotethys subduction. This active accretionary-extensional margin was progressively involved in a collisional phase during the Late Carboniferous. Together, the Évora Massif and the Beja Igneous Complex include three successive stages of bimodal magmatism, with a chemical composition indicative of a long-lived subduction process lasting from the Tournaisian to the Moscovian in the OMZ. The earliest stage of arc magmatism includes the Tournaisian Beja and Torrão gabbro-dioritic rocks of the Layered Gabbroic Sequence. We present new geochemical and Nd isotopic and U-Pb geochronological data for magmatic rocks from the Main (Visean-Serpukhovian) and Latest (Bashkirian-Moscovian) stages of arc magmatism. Visean Toca da Moura trachyandesite and rhyolites and Bashkirian Baleizão porphyries and Alcáçovas quartz diorite share enriched, continental-crust like characteristics, as indicated by major and trace elements, mainly suggesting the addition of calc-alkaline magma extracted from various mantle sources in a subduction-related setting (i.e., Paleotethys subduction). New U-Pb zircon geochronology data have allowed us to establish a crystallization age of 317 ± 3 Ma (Bashkirian) for Alcáçovas quartz diorite that confirms a temporal link with Baleizão porphyry. Positive εNd(t) values for the Carboniferous igneous rocks of the Beja Igneous Complex and the Évora gneiss dome indicate production of new juvenile crust, whereas negative εNd(t) values also suggest different grades of magma evolution involving crustal contamination. The production and evolution of Carboniferous continental crust in the OMZ was most likely associated with the development of an active continental margin during the convergence of the Paleotethys Ocean with Gondwana, involving juvenile materials and different grades of crustal contamination. [ABSTRACT FROM AUTHOR]

Abstract: The Cantabrian Zone of NW Iberia preserves a voluminous, almost continuous, sedimentary sequence that ranges from Neoproterozoic to Early Permian in age. Its tectonic setting is controversial and recent hypotheses include (i) passive margin deposition along the northern margin of Gondwana or (ii) an active continental margin or (iii) a drifting ribbon continent. In this paper we present detrital zircon U–Pb laser ablation age data from 13 samples taken in detrital rocks from the Cantabrian Zone sequence ranging from Early Silurian to Early Permian in depositional age. The obtained results, together with previously published detrital zircon ages from Ediacaran–Ordovician strata, allow a comprehensive analysis of changing provenance through time. Collectively, these data indicate that this portion of Iberia was part of the passive margin of Gondwana at least from Ordovician to Late Devonian times. Zircon populations in all samples show strong similarities with the Sahara Craton and with zircons found in Libya, suggesting that NW Iberia occupied a paleoposition close to those regions of present-day northern Africa during this time interval. Changes in provenance in the Late Devonian are attributed to the onset of the collision between Gondwana and Laurussia. Additionally, the Middle Carboniferous to Permian samples record populations consistent with the recycling of older sedimentary sequences and exhumation of the igneous rocks formed before and during the Variscan orogeny. Late-Devonian to Permian samples yield zircon populations that reflect topographic changes produced during the Variscan orogeny and development of the lithospheric scale oroclinal buckling. [Copyright &y& Elsevier]

Abstract: This research provides the first evidence of prehistoric quarrying of eclogitic rocks on the Iberian peninsula. Such metamorphosed basic igneous rocks are known to have been used in southern Spain and Portugal during late prehistory as a raw material for the making of polished lithic tools (axes, adzes, chisels, and hammers). These rocks were widely used primarily because of their tolerance to blow and friction due to their mineralogical and textural characteristics. We have identified two quarries within the Sierra de Baza Natural Park (Granada), in the Betic Cordillera of southern Spain: Rambla del Agua and Cerro de San Cristóbal. The bedrock geology of these quarries forms part of the Mulhacen Complex Ophiolite Unit (Nevado‐Filábride Domain), which discontinuously outcrops along a 250‐km belt in southeastern Spain. Petrographic and geochemical analyses were conducted on raw materials from quarries in the Sierra de Baza and compared with archaeological materials from different sites in southern Iberia. These analyses allow us to specify the Nevado‐Filábride‐derived lithic source and define exchange networks. Archaeological sites around the studied quarries chronologically date their use between the early Neolithic and Bronze Age (∼5500–1500 B.C.). [ABSTRACT FROM AUTHOR]

Ion microprobe (SIMS) dating shows that three plutonic rock bodies representative of the major, ∼ 015 000 km², late tectonic (late-D3), plutonic rock series in the Central Iberian Zone of the Hercynian belt in west-central Iberia have indistinguishable zircon crystallization ages. Ledrada biotite granite and Colmenar cordierite-bearing biotite granite show gradual transitions in field appearance, petrography and chemistry and have statistically indistinguishable weighted average ages of 306.8 ± 1.9(2σ) Ma and 306.5 ± 1.5(2σ) Ma, respectively, which indicates that they originated during a single event involving a heterogeneous magma which notably varied in Al-content, The third rock body, Navahermosa meta-gabbronorite, has a weighted average zircon crystallization age of 305.6 ± 1.4(2σ) Ma, statistically indistinguishable (variance analysis, F-test, α = 0.05) from the granites. Zircon crystals in the gabbronoritic rock are anhedral, skeletal, millimetre-sized and partake in main magmatic textures, whereas the zircon grains in the granites are of more common appearance, much smaller, usually euhedral and enclosed in main magmatic crystals. As gestation times of granitic zircon, the time between zircon crystallization and magmatic intrusion, may be up to 5 Myr, the crystallization age of the gabbronoritic zircon may be the best estimate of the time of emplacement of the magmatic complex. Our study indicates co-existence of basic and silicic magmas in the Hercynian crustal section at c. 306 Ma, suggesting common genetic control. The two granitic rocks carry inherited zircon ranging from c. 1300 to 330 Ma, indicating that pre-Hercynian basement rocks of Proterozoic to Palaeozoic age contributed to the granitic magma. [ABSTRACT FROM AUTHOR]

Ultramafic (lherzolites, metasomatized peridotites, harzburgites, websterites and clinopyroxenites) and mafic igneous (basalts, dolerites, diorites and gabbros) rocks exposed at the sea-floor along the West Iberia continental margin represent a rare opportunity to study the transition zone between continental and oceanic lithosphere. The igneous rocks are enriched in LREE, unlike North Atlantic MORB. A correlation between their 143Nd/144Nd isotopic composition and Ce/Yb ratio suggests that they originate from mixing between partial melts of a depleted mantle source similar to DMM and of an enriched mantle source which may reside within the continental lithosphere. Clinopyroxenes and amphiboles in the ultramafic rocks are LREE depleted and have flat HREE patterns with concentrations higher than those of abyssal peridotites. Clinopyroxenes in the harzburgites are less LREE depleted but have lower HREE concentrations. The clinopyroxenes in the Galicia Bank (GB) lherzolites have radiogenic Nd (143Nd/144Nd ranging from 0·512937 to 0·513402) and unradiogenic Sr (87Sr/86Sr ranging from 0·702100 to 0·702311) isotopic ratios similar to, or higher than, DMM (Depleted MORB Mantle) whereas the clinopyroxenes in the Iberia Abyssal Plain websterites have low-Nd isotopic compositions (143Nd/144Nd ranging from 0·512283 to 0·512553) with high-Sr isotopic ratios (87Sr/86Sr ranging from 0·704170 to 0·705919). Amphiboles in Galicia Bank lherzolites and diorites have Nd–Sr isotopic compositions (143Nd/144Nd from 0·512804 to 0·512938 and 87Sr/86Sr from 0·703243 to 0·703887) intermediate between those of the clinopyroxenes from the Galicia Bank and the Iberia Abyssal Plain, but similar to the clinopyroxenes in the 5100 Hill harzburgite (143Nd/144Nd = 0·512865 and 87Sr/86Sr = 0·703591) and to the igneous rocks (143Nd/144Nd ranging from 0·512729 to 0·513121 and 87Sr/86Sr ranging from 0·702255 to 0·705109). The major and trace element compositions of cpx in the Galicia Bank spinel lherzolites provide evidence for large-scale refertilization of the lithospheric upper mantle by MORB-like tholeiitic melts. The associated harzburgites did not undergo partial melting during the rifting stage, but, in earlier times, probably during, or even before, the Hercynian orogeny. Iberia Abyssal Plain websterites are interpreted as high-pressure cumulates formed in the mantle. Their high Sm/Nd ratios (from 0·43 to 0·67) coupled with very low-Nd isotopic compositions are best explained by a two-stage history: formation of the cumulates from the percolation of enriched melts long before the rifting, followed by low-degree partial melting of the pyroxenites, accounting for their LREE depletion. This last event probably occurs during the rifting episode, 122 Myr ago. The isotopic heterogeneities observed in the ultramafic rocks of the Iberia margin were already present at the time of the rifting event. They reflect a long and complex history of depletion and enrichment events in an old part of the mantle, and provide strong arguments for a sub-continental origin of this part of the upper mantle. [ABSTRACT FROM AUTHOR]