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The West Iberian Margin (WIM) was a locus of significant post-rift Late Cretaceous magmatism coeval with multiple intraplate magmatic events on the Central-North Atlantic. The effects of the migration of the Iberian microplate on the location of the distinct magmatic occurrences are here investigated.At the WIM and within this magmatic cycle, the Sintra, Sines and Monchique intrusive massifs, the Lisbon Volcanic Complex and distinct sill complexes were emplaced on the onshore continental margin. Several coeval oceanic seamounts, are also evaluated in terms of age and location for the assessment of how plausible the combined effects of plate motion and underlying mantle contributions are to their origin.Using GPlates software we assess the different mantle mechanisms that can explain magmatic upwelling in the region, including: 1) plume, whether static or mobile ones; 2) edge-driven convection; or 3) stationary superplume with secondary plumelets.The preliminary results suggest that a stationary superplume emitting distinct secondary plumelets is the preferred model for the distinct and diachronous magmatic features that pierced the crust as the Iberian microplate moved along a non-linear path. This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020- IDL and UIDB/04035/2020- GeoBioTec.

The West Iberian Margin is a prime example of a magma-poor hyperextended continental margin. However, the margin is punctuated by three discrete Mesozoic magmatic events, from which the last, occurring 20-40 M.a. after complete lithospheric breakup of the Iberia-Newfoundland conjugate margin, is related to the late Cretaceous Atlantic Alkaline Province. It is characterised onshore by multiple outcropping intrusive (Sintra, Sines and Monchique) and extrusive (e.g., the Lisbon Volcanic Complex) alkaline suites of magmatism, and offshore by conspicuous and enigmatic magnetic anomalies, suggesting additional magmatic features.Analysis of seismic reflection and potential field data, from the offshore central segment of the West Iberian Margin, unveiled the evidence of a complete intraplate magmatic plumbing system, comprising the presence of a large intrusive feature, a preserved volcanic edifice with its related lava flows, and the associated network of sills and sill complexes. The intrusive body, the Estremadura Spur Intrusion, is revealed to correspond to a sizeable laccolith of about 530 km3 of rock volume, for which 3D gravity and magnetic inversion and 2D magnetic forward modelling, constrained by seismic data, suggest a composition predominantly granitic. The Fontanelas volcano, cropping out the seafloor and partly buried by latest Cretaceous and Tertiary sediments, is a 2800 m high volcano showing different summits. Internal architecture of the volcano, showing outward dipping reflectors that can be assigned to lava flows and explosive debris, reveals that the composite edifice has grown progressively from multiple vents. Potential field data models suggest the edifice is predominantly of basaltic nature, an aspect supported by previous dredge samples collected at the crest of the volcano, that yielded remnants of basic pillow lavas and hyaloclastites. Additionally, our analysis revealed the presence of two exceptionally well imaged distinct events of extrusive magmatism. The first, preceding the build-up of the volcanic edifice reveals multiple and superimposed fan-shape to tabular crenulated submarine sheet or ‘a'ā lava flows, sourced from a fissure-type feature located SE of the Fontanelas volcano. A second group of lava flows directly associated with the final stages of volcanic build-up, comprises dendritic and lobate lava flows (pahoehoe or submarine flows) blanketing the flank of the edifice. Associated with these magmatic features, numerous sills and sill complexes, characterised by distinct planar to saucer-shaped geometries, comprise the remaining elements of the plumbing system.Our analysis indicates that syn-rift structural inheritance has controlled the locus and tectono-magmatic emplacement of these features piercing the thinned continental crust, that occurred in two pulses: 1) Coniacian-lower Campanian and 2) mid to late Campanian. Moreover, the evidence of a vigorous plumbing system offshore the West Iberian Margin bears implications on models involved in mantle upwelling feeding the Atlantic Alkaline Province since the late Cretaceous, pointing to massive mantle to crust magma transfer tentatively assigned to a resilient mantle plume rooted at the Central-East Atlantic Anomaly.This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) UIDB/04035/2020-GeoBioTec and UIDB/50019/2020-IDL.

SUMMARYMid-plate upward mantle flow is a key component of global mantle convection, but its patterns are poorly constrained. Seismic anisotropy is the most direct way to infer mantle flow as well as melt distribution, yet the convection patterns associated with plume-like mantle upwelling are understudied due to limited seismic data coverage. Here, we investigate seismic anisotropy beneath the Madeira and Canary hotspots using a dense set of shear wave splitting observations and combining teleseismic and local events recorded by three-component broad-band and short-period seismic stations. Using a total of 26 stations in the Madeira archipelago and 43 stations around the Canary Islands, we obtain 655 high-quality measurements that reveal heterogeneous flow patterns. Although local event results are sparse around most islands, we can observe a small average of S-wave splitting times of 0.16 ± 0.01 s, which significantly increase with source depth beneath El Hierro (>20 km) and Tenerife (>38 km) up to 0.58 ± 0.01 and 0.47 ± 0.05 s. This suggests an influence of melt pocket orientation in magma reservoirs developed at uppermost-mantle depths. Likewise, anisotropy increases significantly beneath the islands with shield stage volcanism (up to 9.81 ± 1.78 per cent at El Hierro, western Canaries, against values up to 1.76 ± 0.73 per cent at Lanzarote, eastern Canaries). On average, teleseismic SKS-wave splitting delay times are large (2.19 ± 0.05 s), indicating sublithospheric mantle flow as the primary source for anisotropy in the region. In the Canaries, the western islands show significantly smaller average SKS delay times (1.93 ± 0.07 s) than the eastern ones (2.25 ± 0.11 s), which could be explained by destructive interference above the mantle upwelling. Despite complex patterns of fast polarization directions throughout both regions, some azimuthal pattern across close stations can be observed and related to present-day mantle flow and anisotropy frozen in the lithosphere since before 60 Ma. Additionally, we infer that the current presence of a mantle plume beneath the archipelagos leads to the associated complex, small-scale heterogeneous anisotropy observations.

The magma-poor West Iberian Margin, as part of the Peri-Atlantic alkaline province, records multiple evidence for intra-plate post-rift magmatism. Based on high-resolution multichannel seismic data, this work discusses the presence of large volcanic and intrusive features in the Estremadura Spur, providing evidence for important magmatic activity during the drifting of the continental margin. Our observations reveal distinct voluminous fissure-fed effusive sequences and the details of the 2800 m-high Fontanelas compound volcano, including its external and internal architecture, secondary vents and associated lava flows, all of which were probably extruded at intermediate water depths. Numerous and morphologically diverse sills and sill complexes are also described, attesting to the presence of a Late Cretaceous shallow magmatic plumbing system in the area. Magmatism in this region is interpreted as having occurred during two main pulses and types of activity: 1) Coniacian to lower Campanian(?) age, characterized by fissural and fault-controlled volcanism, which mostly extruded massive lobate/sheet lava flows; and 2) a second voluminous intrusive and extrusive event of mid to late Campanian age, which includes the intrusion of the Estremadura Spur laccolith and the prominent Fontanelas compound volcano with associated dendritic lava flows. The inferred volumes of the first fissure-fed effusive event suggest a large eruption magnitude, comparable to some of the largest historical effusive eruptions. The second magmatic pulse led to the emplacement of discrete clusters of sills and sill complexes, as well as the construction of the ~2.8 km-high Fontanelas volcano, suggesting a syn-rift structural inheritance that controlled the location of the Estremadura Spur Intrusion and the Fontanelas volcanic area. Altogether, a total volume of rock exceeding 1.452 km3 is estimated to have been emplaced or extruded in this region in a relatively short period, attesting to the prominence of the magmatism in this sector of the West Iberian Margin.

A 1:12,000 geological map of the Macao Special Administrative Region has been produced through detailed field work supported by petrographic, mineralogical, geochronological and geochemical data obtained in previous studies. This map aims to represent a reliable tool to understand the geological evolution of the region and for management of the territory. The geology of Macao is dominated by two groups of Jurassic granitic rocks belonging to an intrusive suite located along the coast of Southeast China: Macao Group I (MGI: 164.5 ± 0.6 to 162.9 ± 0.7 Ma) and Macao Group II (MGII: 156.6 ± 0.2 to 155.5 ± 0.8 Ma), including the associated microgranite, aplite and pegmatite dikes and quartz veins. Remnants of the metasedimentary wall-rock are present as Devonian xenoliths enclosed within the granites. Younger Jurassic to Cretaceous andesite to dacite dikes (150.6 ± 0.6 to

The widespread W-(Mo)-Sn-Nb-Ta polymetallic mineralization in Southeast (SE) China is genetically associated with Mesozoic highly fractionated granitic rocks. Such rocks have enigmatic mineralogical and geochemical features, making its petrogenesis an intensely debated topic. To better understand the underlying magma evolution processes, petrography, garnet chemistry and whole-rock major and trace element data are reported for Jurassic highly fractionated granitic rocks and associated microgranite and aplitepegmatite dikes from Macao and compared with coeval similar granitic rocks from nearby areas in SE China. Despite the fact that the most evolved rocks in Macao are garnet-bearing aplite-pegmatite dikes, the existence of coeval two-mica and garnet-bearing biotite and muscovite granites displaying more evolved compositions (e.g, lower Zr/Hf ratios) indicates that the differentiation sequence reached higher degrees of fractionation at a regional scale. Although crystal fractionation played an important role, late-stage fluid/melt interactions, involving F-rich fluids, imparted specific geochemical characteristics to Macao and SE China highly fractionated granitic rocks such as the non-CHARAC (CHArge-and-RAdius-Controlled) behavior of trace elements, leading, for example, to non-chondritic Zr/Hf ratios, Rare Earth Elements (REE) tetrad effects and Nb-Ta enrichment and fractionation. Such process contributed to the late-stage crystallization of accessory phases only found in these highly evolved facies. Among the latter, two populations of garnet were identified in MGI (Macao Group I) highly fractionated granitic rocks: small grossular-poor euhedral grains and large grossular-rich skeletal garnet grains with quartz inclusions. The first group was mainly formed through precipitation from highly evolved Mn-rich slightly peraluminous melts under low-pressure and relatively low temperature (∼700 °C) conditions. Assimilation of upper crust metasedimentary materials may have contributed as a source of Mn and Al to the formation of garnet. The second group has a metasomatic origin related to the interaction of magmatic fluids with previously crystallized mineral phases and, possibly, with assimilated metasedimentary enclaves or surrounding metasedimentary strata. The highly fractionated granitic rocks in Macao represent the first stage in the development of granite-related W-(Mo)-Sn-Nb-Ta mineralization associated with coeval more evolved lithotypes in SE China.

The Figueira de Castelo Rodrigo–Lumbrales Anatectic Complex (FCR-LAC) located in the Central Iberian Zone of the European Variscan Belt is delimited by two shear zones, which have been interpreted as constraining its exhumation. New U–Pb zircon and apatite ages for the migmatites allowed us to obtain a peak metamorphic age of the anatectic complex (316.8 ± 2.0 Ma), and to estimate fast cooling (7–54°C Ma –1 ) and fast exhumation (0.2–1.3 mm a −1 ) after a vertical displacement of c. 6–9 km. Our results show a similar zircon age distribution between migmatites and the Excomungada Formation from the host Ediacaran–Cambrian Douro–Beiras Supergroup. Although the existence of an inherited zircon population lasting c. 500 Ma, absent in the metasedimentary units, suggests the contribution of Ollo de Sapo magmatic rocks during the Lower–Middle Pennsylvanian melting events. Detrital zircon ages of the Pinhão Formation (Douro Group) have contrasting sources to units from the Beiras Group, which may indicate the presence of a barrier that prevented older detrital components from reaching the Douro basin. However, at odds with what has been postulated before, such a barrier must have been placed farther south of the FRC-LAC, and thus not coincident with the Juzbado–Penalva do Castelo shear zone. Supplementary material: A full description of the stratigraphy and lithologies (Supplementary 1 and 2, respectively); the analytical conditons of the LA-ICP-MS analyses (Supplementary Material 3); the U–Pb zircon and apatite data of the FCR-LAC migmatites and the U–Pb detrital zircon data of the DBSG (Supplementary Material 4) are available at https://doi.org/10.6084/m9.figshare.c.6002006

[Abstract The combined effects of post‐rift magma emplacement and tectonic inversion on the hyper‐extended West Iberian Margin are unravelled in detail using multichannel 2D/3D seismic data. The Estremadura Spur, acting as an uplifted crustal block bounded by two first‐order transfer zones, shows evidence of four post‐rift tectonic events each with a distinctive seismic‐stratigraphic response that can be used to demonstrate the tectono‐magmatic interplay, namely: (a) the Campanian onset of magmatism (including the Fontanelas Volcano, the widespread evidence of multiple sill complexes and the detailed description of a >20 km long laccolith, the Estremadura Spur Intrusion; (b) the Campanian‐Maastrichtian NE‐SW event pervasively affecting the area, resulting in regional uplift, reverse faulting and folding; (c) the Paleocene‐mid Eocene inversion that resulted in widespread erosion and; (d) the Oligocene‐mid Miocene evidence of rejuvenated NW‐SE inversion marked by crestal faulting and forced‐fault folding establishing the final geometry of the area. The distinct deformation styles within each tectonic phase document a case of decoupled deformation between Late Cretaceous and Tertiary units, in response to the predominant stress field evolution, revealing that the magnitude of Late Cretaceous inversion is far more significant than the one affecting the latter units. A detailed analysis of the laccolith and its overburden demonstrate the distinct deformation patterns associated both with magma ascent (including extensional faulting, forced‐folding and concentric reverse faulting) and its interference as a rigid intrusive body during subsequent transpressive inversion. This reinforces the role that the combined tectono‐magmatic events played on the margin. Also analysed is the wider impact of post‐rift magmatism and the associate emplacement of sub‐lithospheric magma on the rheology of a thinned continental crust. This takes into account the simultaneous tectonic inversion of the margin, the implied alternative views on characteristic heat flow, and on how these can be incorporated in source rock organic maturity modelling., The combined effects of multiphase margin inversion and Late Cretaceous magmatism on the Central West Iberian Margin reveals that deformation is decoupled between Cretaceous and Tertiary strata, with a laccolith accommodating significant shortening and acting as a rigid body. ]

Much controversy has occurred in the past few decades regarding the nature of the sources, the petrogenetic processes, and the tectonic regime(s) of the Jurassic magmatism within the Southeast China magmatic belt. This study aims to contribute to the discussion with mineral chemistry, and whole-rock element and Sr-Nd-Hf-Pb isotopic geochemical data from granitic rocks and microgranular mafic enclaves from Macao, where two discrete groups of I-type biotite granites have been identified (referred to as Macao Group I [MGI] and Macao Group II [MGII]). It is proposed that the granitic magmas were generated by partial melting of infracrustal medium- to high-K, basaltic Paleoproterozoic to Mesoproterozoic protoliths (Nd depleted mantle model age [TDM2] = 1.7–1.6 Ga and Hf TDM2 = 1.8–1.6 Ga), triggered by underplating of hot mantle-derived magmas in an extensional setting related to the foundering of a previously flat slab (paleo–Pacific plate) beneath the SE China continent. The main differences between the two groups of Macao granites are attributed to assimilation and fractional crystallization processes, during which upper-crustal Paleozoic metasediments were variably assimilated by MGI magmas. This is evidenced by an increase in initial 87Sr/86Sr ratios with degree of evolution, presence of metasedimentary enclaves, and high percentage of zircon xenocrysts with Paleozoic ages. In addition, other processes like late-stage fluid/melt interaction and magma mixing also left some imprints on granite compositions (rare earth element tetrad effect plus non–charge-and-radius-controlled behavior of trace elements and decoupling between different isotope systems, respectively). The distribution of isotopically distinct granites in SE China reflects the nature of the two Cathaysia crustal blocks juxtaposed along the Zhenghe-Dapu fault.

In the Central Atlantic archipelagos – the Canaries, Cape Verde, Madeira and the Azores – tsunami hazard is often regarded as low, when compared with other extreme wave events such as hurricanes and storms. The geological record of many of these islands, however, suggests that tsunami hazard may be underestimated, notwithstanding being lower than in areas adjacent to subduction zones, such as the margins of the Pacific and Indian oceans. Moreover, tsunamis in oceanic islands are generally triggered by local large-scale volcanic flank collapses, for which little is known about their frequency, making it difficult to estimate the probability of a new occurrence. Part of the problem lies in the fact that tsunami deposits are usually difficult to date, and few islands in the world exhibit evidence for repeated tsunami inundation on a protracted timescale. This study reports on the presence of abundant tsunami deposits (conglomerates and sandstones) on Maio Island (Cape Verde) and discusses their stratigraphy, sedimentological characteristics, probable age and tsunamigenic source. Observations indicate that four distinct inundation events of variable magnitude took place during the Pleistocene. One of the tsunami deposits yielded a high-confidence U/Th age of 78.8 +- 0.9 ka, which overlaps within error with the 73 +- 7 ka age proposed for Fogo volcano’s flank collapse, an event known to have had a significant tsunami impact on nearby Santiago Island. This shows that the Fogo tsunami also impacted Maio, resulting in runups in excess of 60 m above coeval sea-level at ca 120 km from the source. Two older deposits, possibly linked to recurrent flank collapses of the Tope de Coroa volcano in Santo Antão Island, yielded lower-confidence ages of 479 to 390 ka and 360 to 304 ka. A younger deposit (

The West Iberian Margin (WIM) is a key example of a magma-poor passive margin, punctuated by several postrift magmatic manifestations that are part of the Late Cretaceous Atlantic Alkaline Province. In this work, potential field (gravity and magnetics) data, constrained by 3D multichannel seismic reflection data, are used to describe and characterise the geometry and nature of magmatic features located offshore the central segment of the margin, the Estremadura Spur. The estimated geometry and nature of the magmatic features was achieved through the integration of 3D gravity and magnetic inversion and 2D magnetic forward modelling. The results provide an insightful 3D subsurface model revealing that: 1) the Estremadura Spur Intrusion represents a 28 x 15 km wide laccolith with an overall granitic nature and an estimated density of 2490-2640 kg/m3 and 0.01-0.05 SI magnetic susceptibility, 2) the 26 x 17 km Fontanelas buried volcano is dominantly basaltic, with density values of 2500-2821 kg/m3 and magnetic susceptibility of 0.01 to 0.0875 SI, and 3) multiple sill complexes intruded the region, thus producing a higher magnetic background on otherwise inconspicuous anomalies The models allowed achieving a confident fit suggesting that both the ESI and the Fontanelas volcano are coeval with the outcropping magmatic features from this same magmatic event. Additionally, the results support that Late Cretaceous alkaline magmatism on the West Iberian Margin is more significant than anticipated and provide further evidence to clarify unclear geometrical aspects of similar intrusions observed onshore. Acknowledging the geometry and nature of these magmatic entities allows to better understand the role of postrift intra-plate magmatism on continental hyper-extended rifted margins by clarifying how shallow plumbing systems evolve in these settings. info:eu-repo/semantics/publishedVersion

The Canary and Madeira archipelagos are two hotspots in the Eastern Atlantic (27º to 33º N) that are close (430 km) to each other. Their volcanism is thought to be caused by distinct mantle upwellings. Recent high resolution regional P-wave and S-SKS wave tomography images of the Ibero-western Maghrebian region show subvertical low velocity anomalies under the Canaries, the Atlas ranges and the Gibraltar Arc extending across all the upper mantle to the surface. The anomaly below the Canary archipelago and the Atlas are rooted beneath the mantle transition zone (MTZ) and appear to be connected to a broad and strong low-velocity anomaly in the lower mantle. Beneath Madeira, the slow anomaly has a blob-like shape and is only observed down to ~ 300 km depth, suggesting differences in the development stages of the upwellings at the origin of the two hotspots.The globally observed 410 and 660 upper-mantle seismic discontinuities are primarily linked to mineral phase transitions in olivine and the study of their local depth variations constrains the intra-mantle heat and mass transfer processes. The presence of discontinuities that are not globally observed may indicate the presence of compositional heterogeneities. For example, a sharp discontinuity has been detected at a depth of around 300 km (named the X discontinuity) beneath several hotspots (including the Canaries one) that could prove that the dominant peridotitic mantle mantle is locally enriched in basalt compositions. Here, we investigate the fine structure of the upper mantle beneath the Canary and Madeira volcanic provinces by means of P-to-S conversions at mantle discontinuities from teleseismic events recorded at 42 seismic stations (24 in the Canaries and 18 in Madeira). We compute 1304 high quality receiver functions (984 in the Canaries and 320 in Madeira) and stack them in the relative time-slowness domain to identify discontinuities in the 200-800 km depth range. Receiver functions are computed in different frequency bands to investigate the sharpness of the observed discontinuities. From the analysis of stacked receiver functions, we obtain robust and clear converted phases from the globally detected 410 and 660 discontinuities beneath both volcanic provinces. However, a reflector at ~300 km depth is only observed beneath the Canaries. For the Canary’s dataset we also detect multiples (Ppds, where d is the discontinuity depth) from the reflector at 300 km and from the 410 discontinuity while for the Madeira’s one, we only detect multiples from the 410. This study allows for a detailed comparison between the two archipelagos. The analysis of arrival times and amplitude of detected phases helps constraining the depth, width, and velocity jump of the observed discontinuities. These parameters and their interpretation based on mineral physics will add new constraints to the understanding of the geodynamical context of the Canary Island and Madeira hotspots. This is a contribution to project SIGHT (SeIsmic and Geochemical constraints on the Madeira HoTspot; Ref. PTDC/CTA-GEF/30264/2017). The authors would like to acknowledge the financial support of FCT through project UIDB/50019/2020 – IDL.

The NE–SW trending Tiddas Souk Es-Sebt des Ait Ikko (TSESDAI) basin, located at 110 km southeast of Rabat, in the region of Khmesset between the village of Tiddas Souk Es-Sebt des Ait Ikko, is the third largest late Palaeozoic continental trough in the northern Central Moroccan Meseta. It is a ~20 km long and ~2–3 km wide basin, comprising mainly mixed volcano-sedimentary reddish-purple continental Permian rocks laying with an angular unconformity on Visean deep marine siliciclastic sediments and unconformably overlain by the Triassic and Cenozoic formations. In this study we aim to better determine the age of Permian volcanics and their chemical and mineralogical characteristics, as well as assess the provenance of inherited zircons, thus contributing to the understanding of the late stages of the Variscan orogeny in Morocco. The standard volcanic succession includes the following terms: (i) andesites, lapilli tuffs and andesitic ash deposits, (ii) accumulations of rhyolitic lavas, (iii) lapilli tuffs and rhyolitic ash (formation F1), (iv) flows and breccias of dacites, (v) andesite flows, and (vi) basaltic flows. The various volcanic and subvolcanic studied rocks display calc-alkaline-series characteristics with high contents of SiO2, Al2O3, CaO, MgO, and relatively abundant alkalis, and low contents of MnO. In the classification diagram, the studied facies occupy the fields of andesites, trachy-basalts, dacites, trachydacites, and rhyolites and display a sub-alkaline behavior. These lavas would be derived from a parental mafic magma (basalts) produced by partial fusion of the upper mantle. Specific chemical analyses that were carried out on the mineralogical phases (biotite and pyroxene) revealed that the examined biotites can be classified as magnesian and share similarities with the calc-alkaline association-field, while the clinopyroxenes are mainly augites and plot on the calc-alkaline orogenic basalt field. Andesites and dacites of TSESDAI show similarities with the rocks of the calc-alkaline series not linked to active subduction and which involve a continental crust in their genesis. The existence of enclaves in the lavas of the TSESDAI massif, the abnormally high contents of Rb, Ba, Th, and La, and the systematic anomalies in TiO2 and P2O5 indicate also a crustal contamination mechanism. Three magmatic episodes are distinguished with two episodes that correspond to an eruptive cycle of calc-alkaline andesites and rhyolites followed by a basaltic episode. The SHRIMP U–Pb geochronologic data of zircons recovered from the rhyolite dome of Ari El Mahsar in TSESDAI basin show a Concordia age of 286.4 ± 4.7 Ma interpreted to date the magmatic crystallization of this dome. Thus, the rhyolite likely belongs to the third magmatic episodes of TSESDAI.

Understanding the exhumation of middle to lower crustal rocks is of utmost importance to unravel intracrustal mass transfer processes during orogenic build-up. The Figueira de Castelo Rodrigo–Lumbrales Anatectic Complex (FCR–LAC) is located within the autochthonous terrane of the Variscan Central Iberian Zone and is an example of the association between S-type granites and migmatites. The anatectic complex contacts to the north and south with low-grade metamorphic units through the Huebra and Juzbado–Penalva do Castelo shear zones, respectively. Integration of new U–Pb zircon and apatite age data allowed us to obtain Variscan crystallization ages, inherited zircon ages and unprecedented cooling rates for different facies of the FCR–LAC granites. The zircon crystallization ages mostly cluster around 313–317 Ma for the syn-tectonic granites, whereas the dated late-tectonic granite provided an age of 300 Ma. The cooling rates range from 13 to 35 °C Ma−1, which implies fast exhumation (0.3–0.84 mm a−1) and shallow emplacement (ca. 8 km deep), compatible with exhumation facilitated by large crustal-scale shear zones. Inherited zircon in the granites reveals melting of Cadomian metasediments (650–550 Ma), Upper Cambrian–Lower Ordovician (495–470 Ma) metaigneous rocks (Ollo de Sapo formation) and of minor older components, suggesting protolith affinity with the Northern Domain of the Central Iberian Zone.

Post-collisional potassium-rich rocks are a critical petrogenetic and geodynamic marker across the European Variscan Belt. We present a detailed characterization of the only potassium-rich mafic intrusions identified so far in the Ossa-Morena Zone (Iberian Massif). Using new major, trace and Smsingle bondNd isotopic whole-rock analyses, as well as mineral chemistry analyses, we discussed the petrogenesis of the early Carboniferous potassium-rich Veiros and Vale de Maceira (Portugal) stocks in the geotectonic framework of the southern Iberia, marked by the collision of the Ossa-Morena Zone, a Gondwanan terrane, with the South Portuguese Zone, a Laurussian terrane. The Veiros and Vale de Maceira shoshonites (s.l.) range from gabbros to syenites, with a predominance of monzonites and monzogabbros, characterized by different proportions of olivine, clinopyroxene, orthopyroxene, plagioclase, alkali feldspar, phlogopite and brown hornblende. The Veiros stock is mainly composed of fine-grained ultrapotassic rocks, and the Vale de Maceira stock is composed chiefly of medium-grained shoshonite rocks. A small group of hornblende-bearing medium-grained calk-alkaline rocks was also identified. The stocks have high contents of K2O, MgO, total alkalis, Th and other LILE, high ratios of LREE/HREE and LREE /HFSE, and show a Nb-Ta-Ti negative anomaly, typical of orogenic settings. Sr and Nd isotopes yielded moderate radiogenic Sr and unradiogenic Nd, that might suggest the involvement of a crustal component. However, the combined use of isotopic and elemental compositions rules out significant contamination by crustal materials upon ascent and emplacement. Instead, a source metasomatised by subduction-related fluids and hydrous melts from the slab is proposed. This diversely metasomatised source was a phlogopite-amphibole-bearing and (phlogopite-free) amphibole-bearing lherzolite at the upper part of the garnet stability field in the sub-continental lithospheric mantle. The Devonian mafic volcanic rocks point to a northward dipping (present coordinates) subduction of the Rheic oceanic plate underneath the Ossa-Morena Zone during the Variscan Orogeny. However, the Veiros and Vale de Maceira magmas originated during the post-collisional stage from the partial melting of the supra-subduction metasomatized lithosphere. The melting occurred during a period of enhanced heat due to asthenospheric upwelling related to the slab break-off of the Rheic's slab. The stocks are concomitant with the profusion of granitoid intrusions, which is compatible with a post-collisional tectonic setting. They are also coeval with the opening of the Beja-Acebuches back-arc, likely related to slab roll-back of a segment of the Rheic oceanic crust, implying polyphasic subduction and a complex geodynamic setting for the late stages of oceanic closure in southern Iberia. published

An edited version of this paper was published by AGU. Copyright (2001) American Geophysical Union., The Canary and Madeira provinces in the Central-East Atlantic Ocean are characterized by an irregular spatio-temporal distribution of volcanism along the hotspot tracks, and several alternative scenarios have been suggested to explain it. Here, we combine results from seismic tomography, shear-wave splitting and gravity along with plate reconstruction constraints to investigate the mantle structure and dynamics beneath those provinces. We find that the Central-East Atlantic Anomaly (CEAA), which rises from the core-mantle boundary and stalls in the topmost lower mantle, is the deep source of distinct upper-mantle upwellings beneath the region. The upwellings detach intermittently from the top of the CEAA and appear to be at different evolutionary stages. We argue that the accumulation of plume material in the topmost lower mantle can play a key role in governing the first-order spatio-temporal irregularities in the distribution of hotspot volcanism.

The Canary and Madeira provinces, located in the central-east Atlantic Ocean, are characterized by irregularly distributed hotspot tracks displaying large age differences and variable distances between volcanoes. For this reason, the geodynamic mechanism(s) that control the spatio-temporal patterns of volcanism are still unclear. Here, we use results from seismic tomography, shear-wave splitting, and gravity to show that the Central-East Atlantic Anomaly (CEAA), rising from the African large low-shear-velocity province and stalled in the topmost lower mantle, is the source of distinct upper-mantle diapirs feeding those provinces. The diapirs detach intermittently from the CEAA and seem to be at different evolutionary stages. Geochemistry data confirm the lower-mantle origin of the diapirs, and plate reconstructions constrain their temporal evolution. Our observations suggest that the accumulation of deep plume material in the topmost lower mantle can play a significant role in governing the spatio-temporal distribution of hotspot volcanism.This is a contribution to project SIGHT (Ref. PTDC/CTA-GEF/30264/2017). The authors would like to acknowledge the financial support FCT through project UIDB/50019/2020 – IDL.

The Madeira and Canary archipelagos, located in the eastern North Atlantic, are two of many examples of hotspot surface expressions, but a better understanding of the crust and upper mantle structure beneath these regions is needed to investigate their structure in more detail. With the study of seismic anisotropy, it is possible to assess the rheology and structure of asthenosphere and lithosphere that can reflect a combination of mantle and crustal contributions.Here, as part of the SIGHT project (SeIsmic and Geochemical constraints on the Madeira HoTspot), we present the first detailed study of seismic anisotropy beneath both archipelagos, using data collected from over 60 local three-component seismic land stations. Basing our observations on both teleseismic SKS and local S splitting, we are able to distinguish between multiple layers of anisotropy. We observe significant changes in delay time and fast shear-wave orientation patterns on short length-scales on the order of tens of kilometres beneath the western Canary Islands and Madeira Island. In contrast, the eastern Canary Islands and Porto Santo the pattern is much more uniform. The detected delay time increase and more complex orientation patterns beneath the western Canary Islands and Madeira can be attributed to mantle flow disturbed and diverted on small-length scales by a strong vertical component. This is a clear indication of the existence of a plume at each of those archipelagos, nowadays exerting a strong influence on the western and younger islands. We therefore conclude that a plume-like feature beneath Madeira exists in a similar way to the Canary Island hotspot and that regional mantle flow models for the region should be reassessed.This is a contribution to project SIGHT (Ref. PTDC/CTA-GEF/30264/2017). The authors would like to acknowledge the financial support FCT through project UIDB/50019/2020 – IDL.

The Khzama ophiolite is a highly dismembered complex located in the Siroua inlier of the Moroccan Anti-Atlas Belt. It consists of ultramafic rocks, cumulate gabbros, sheeted dikes, pillow lavas, and an overlying volcano-sedimentary sequence. Three main tectonic slices of sheeted dike complexes are studied in detail along three rivers, exposing well preserved outcrops where individual dikes are clearly distinguishable from the intruded host rock (Assif n&rsquo, Tinzla, Assif n&rsquo, Tasriwine, and Assif n&rsquo, Iriri). Sheeted dikes of the Khzama ophiolitic complex are basaltic to andesitic in composition, displaying a clear sub-alkaline nature. We identify two sets of dikes that originate from lower High-Ti series (HTS) lavas and overlying upper Low-Ti series (LTS) lava. The immobile trace-element signatures of these rocks point to a genesis on a backarc environment with magmas sourced in a supra-subduction zone (SSZ) at the spinel peridotite zone. The obtained SHRIMP U-Pb data of the gabbro represent the first radiometric age of zircon extracted from the mafic rocks that were intruded by the sheeted dike complex of the Khzama ophiolite. These grains yield a concordia age of 763 &plusmn, 5 Ma, which is consistent with the 761.1 + 1.9/&minus, 1.6 and 762 + 1/&minus, 2 Ma U-Pb zircon ages of plagiogranites of Siroua. Based on their mineralogy, modal proportions, and major element chemistry, the felsic dikes are classified as high silica&ndash, low alumina trondhjemites or plagiogranites. These plagiogranites were likely formed by the partial melting of mafic rocks rather than by extreme fractional crystallization. A plagiogranite dated at 777 &plusmn, 4.7 Ma (U-Pb on zircon) is significantly older than the ca. 762 Ma plagiogranites previously recorded for the Khzama locality, suggesting a long-lived supra-subduction zone (SSZ) with conditions for the hydrous melting of mafic rocks.

Late Cretaceous Neyriz ophiolite, as a part of the Outer Zagros Ophiolitic Belt, represents a remnant of the southern Neo-Tethyan oceanic lithosphere exposed along the Zagros suture zone in the south of Iran. Neyriz ophiolite is composed of dismembered lithological units including variably depleted mantle peridotites as well as intrusive and extrusive rocks preserving a geochemical evolution from mid-ocean ridge (MORB) to subduction-related (boninitic) signatures. Initially, the southern Neo-Tethyan oceanic lithosphere formed in the mid-ocean ridge spreading centre between the Arabian plate to the south west and the Eurasian plate to the north east. The inception of intra-oceanic subduction in the northern margin of the Arabian plate caused a slightly metasomatised supra-subduction-zone (SSZ) mantle lithosphere, producing MORB-like melts with a high degree of partial melting (~25–30%), and complementary depleted residual clinopyroxene (Cpx)-rich harzburgite. The zircon U-Pb geochronology for plagiogranite and gabbro intrusions reveals formation ages of 100.1 ± 2.3 Ma to 93.4 ± 1.3 Ma, respectively (Cenomanian). At a later stage, the rapid slab rollback and associated fore-arc spreading led to asthenospheric diapirism and arc-wedge mantle corner flow, which produced boninitic-like melts with advanced degrees of shallow partial melting (~35%), and ultra-depleted residual Cpx-poor harzburgites. The pervasive interaction between boninitic-like melts and refractory Cpx-poor harzburgites produced dunites as replacive lenses. Thus, this study postulates that Neyriz ophiolite formed from the Neo-Tethyan intra-oceanic subduction system, and preserves evidence of the evolution from an early-MORB oceanic crust to an extending fore-arc basin during subduction rollback processes. This tectonic environment is common in the Eastern Mediterranean region, where SSZ ophiolites have resulted in extended protoarc-forearc settings above subducted slabs.

One of the most remarkable natural events on Earth are the large lateral flank collapses of oceanic volcanoes, involving volumes of rock exceeding tens of km3. These collapses are relatively frequent in recent geological times as supported by evidence found in the geomorphology of volcanic island edifices and associated debris flows deposited on the proximal ocean floor. The Island of Fogo in the Cape Verde archipelago is one of the most active and prominent oceanic volcanoes on Earth. The island has an average diameter of 25 km and reaches a maximum elevation of 2829 m above sea level (m a.s.l.) at Pico do Fogo, a young stratovolcano located within a summit depression open eastward due to a large lateral flank collapse. The sudden collapse of the eastern flank of Fogo Island produced a megatsunami ~73 ky ago. The limits of the flank collapse were deduced as well from geomorphologic markers within the island. The headwall of the collapse scar is interpreted as either being located beneath the post-collapse volcanic infill of the summit depression or located further west, corresponding to the Bordeira wall that partially surrounds it. The magnetotelluric (MT) method provides a depth distribution of the ground resistivity obtained by the simultaneous measurement of the natural variations of the electric and magnetic field of the Earth. Two N-S magnetotelluric profiles were acquired across the collapsed area to determine its geometry and boundaries. The acquired MT data allowed the determination of the limits of the collapsed area more accurately as well as its morphology at depth and thickness of the post-collapse infill. According to the newly obtained MT data and the bathymetry of the eastern submarine flank of Fogo, the volume involved in the flank collapse is estimated in ~110 km3. This volume –the first calculated onshore– stands between the previously published more conservative and excessive calculations –offshore– that were exclusively based in geomorphic evidence. The model for the summit depression proposing two caldera collapses preceding the collapse of the eastern flank of Fogo is supported by the MT data.

Extrusive carbonatite ash tuff (Tantum) and spatter (Monte Miranda) deposits, and topsoils (incipient and shallow) from both sites of Brava Island (Cape Verde archipelago) were studied by neutron activation analysis, X-ray diffraction and Mossbauer spectroscopy. The ash tuff deposit near Tantum, here reported for the first time, corresponds to an extrusive calciocarbonatite with high W, Th, U and REE contents and a positive Eu anomaly. Similar REE patterns and W concentrations were also found in the spatter deposit of Monte Miranda. Magnetite is the major iron containing phase in both extrusive carbonatite deposits. High W and REE concentrations associated with the presence of calcite prevail in topsoils with extrusive carbonatite influence. In the topsoil developed on extrusive carbonatite ashes, magnetite is well preserved particularly in the coarser fractions probably due to the recent age of the parent material associated with the semi-arid climate of the island; a significant chemical heterogeneity of the whole samples as well as of the different size fractions of these topsoils was found, with an enrichment of Co, Zn, Ga, As, Br, Rb, Ce, and particularly Sb and W in the clay-size fraction, which may be relevant for the study of environmental health issues in Brava Island.

Madeira and the Canary Islands, located in the eastern North Atlantic, are two of many examples of hotspot surface expressions. Their tracks have been reconstructed to past locations close to the south-western part of the Iberian Peninsula and north-western Africa, respectively. Furthermore, due to their close proximity, an interconnected origin of these two hotspots has been proposed but details remain unclear. A better understanding of the crust and upper mantle structure beneath these islands is needed to investigate this potential connection.The subsurface structure has an influence on the stress field, which can be investigated studying seismic anisotropy patterns of the region. Seismic anisotropy leads to variations in the speed of seismic waves as a function of the direction of wave propagation. In the crust an orientation in the direction of maximum stress is observed, commonly being parallel to the alignment of fractures or cracks. In the upper mantle the orientation is influenced by mantle flow. A widely used method to identify anisotropy is the observation of shear-wave splitting of data from teleseismic events. In case of multiple anisotropic layers, including measurements from local events it is possible to distinguish crustal from upper mantle influences.As part of the SIGHT project (SeIsmic and Geochemical constraints on the Madeira HoTspot), we carried out the first detailed study of seismic anisotropy beneath both archipelagos, using teleseismic SKS and local shear-wave splitting measurements of data collected from land stations of seismic networks located on Madeira and the Canary Islands.Significant changes, both in orientation and delay time, can be observed on short length-scales on the order of tens of kilometres, matching major geological features such as, for example, the major rift zone on Madeira island. In a further step, we compare these results to previous studies of crustal and upper mantle anisotropy focusing on north-western Africa and the Iberian Peninsula to investigate the nature of the lithospheric corridor between the present day hotspot positions and the Atlas-Gibraltar region.This is a contribution to project SIGHT (Ref. PTDC/CTA-GEF/30264/2017). The authors would like to acknowledge the financial support FCT through project UIDB/50019/2020 – IDL.

Cape Verde is an intraplate archipelago located in the Atlantic Ocean about 560 km west of Senegal, on top of a ~130 Ma sector of the African oceanic lithosphere. Until recently, due to the lack of broadband seismic stations, the upper-mantle structure beneath the islands was poorly known. In this study we used data from two temporary deployments across the archipelago, measuring the phase velocities of Rayleigh-waves fundamental-modes in a broad period range (8–250 s), by cross-correlating teleseismic earthquake data between pairs of stations. Deriving a robust average, phase-velocity curve for the Cape Verde region, we inverted it for a shear-wave velocity profile using non-linear gradient search.Our results show anomalously low velocities of ∼4.2 km/s in the asthenosphere, indicating the presence of high temperatures and, eventually, partial melting. This temperature anomaly is probably responsible for the thermal rejuvenation of the oceanic lithosphere to an age as young as about 30 Ma, which we inferred from the comparison of seismic velocities beneath Cape Verde and the ones representing different ages in the Central Atlantic.The present results, together with previously detected low-velocity anomalies in the lower mantle and relatively He-unradiogenic isotopic ratios, also suggest a hot plume deeply rooted in the lower mantle, as the origin of the Cape Verde hotspot.The authors would like to acknowledge the financial support FCT through project UIDB/50019/2020 – IDL and FIRE project Ref. PTDC/GEO- GEO/1123/2014.

The last eruption on Fogo Island (Cape Verde Archipelago) occurred in 2014-2015, with mostly hawaiian and strombolian but sometimes vulcanian activity, with variable emission rates of lava flows, pyroclasts and gases (SO2 and CO2). Some lava flows, mainly from the first stage of the eruption enclosed small granular ultramafic nodules (1-3cm), with angular to rounded shapes. The host rocks are porphyritic tephrites, with Ti-augite and Ti-magnetite phenocrysts and, sometimes, amphibole xenocrysts in a brown glassy matrix including laths of plagioclase, clinopyroxene and Ti-mgnetite.The nodules are composed of an early crystallization phase olivine, in subheuedral crystals devoid of kink-bands or in rounded crystals enclosed in clinopyroxene oikocrysts. Clinopyroxene occurs in subeuhedral to anhedral zoned crystals, sometimes partially patchy replaced by late igneous amphibole which also occurs as primary crystals as well as in some xenocrysts. In both cases they frequently show reaction rims with transformation in rhonite, most probably resulting from degassing. Oxide minerals are present as a minor component occurring in sub-euhedral to anhedral crystals as inclusions in olivine and clinopyroxene or interstitially between silicate minerals.The typical cumulus textures, and the mineral chemistry already obtained for the ultramafic nodules from the 2014 eruption at Fogo strongly suggest that they have a cumulate origin and are cognate with the host magmas. Indeed, the similar composition of Ti- augites from the nodules and phenocrysts (Wo49-51 En42-36 Fs12-10), as well as the olivine Fo contents and high CaO contents in olivine are explained by crystal segregation from the same magma of the host rock.Geothermobarometric calculations point to crystallization temperatures for the cumulates between 1150 and 1200 ºC and pressures around 7- 10 kbar, while phenocrysts in host rocks crystallized at around 1000 ºC, and pressures of 3-4. These data confirm the existence of a polybaric plumbing system feeding the 2014-15 Fogo eruption, with some of the reservoirs having developed at mantle depths (at least 22 km). This research received financial support from FCT (Fundação para a Ciência e Tecnologia) through project FIRE (PTDC/GEO-GEO/1123/2014).

International audience; U–Pb geochronology of magmatic and detrital zircons (Zenaga and Bou Azzer-El Graara inliers, Anti-Atlas Belt, Morocco) and a reassessment of the published constraints suggest a revised stratigraphic framework for the lower Anti-Atlas Supergroup. Five major unconformity-bounded lithostratigraphic packages are here distinguished: the two lower units of Paleoproterozoic age are named the Tasserda-Taghatine Group (2030–1706 Ma) and the Oumoula (Mimount) Formation (ca. 1745–1650 Ma); the third unit of Paleoproterozoic to Neoproterozoic age (ca. 1650 to >883 Ma) is the Tizi n’Taghatine Group; the fourth and fifth units of Neoproterozoic age are the ca. 883 Ma Tachdamt and the ca. 700 Ma Bleida formations. Implications of this revised stratigraphic framework include: 1) the Tasserda-Taghatine Group might be linked to the post-orogenic collapse after the Eburnean Orogeny; 2) the Tizi n’Taghatine Group might be ca. 1.1 Ga in age based on proposed correlation with the Taoudeni Basin succession in Mauritania; 3) the Bleida Formation likely reflects deposition in the foreland basin at the early stage of the Pan-African Orogeny; 4) the Oumoula (Mimount) Formation, Tizi n’Taghatine Group, and Tachdamt Formation potentially record extensional events within the Nuna/Columbia and Rodinia supercontinents; 5) the provenance of the lower Anti-Atlas Supergroup (based on our new detrital zircon dating) is mainly from the West African craton along with possible contributions from other cratons such as Amazonia and the Sahara Metacraton; 6) the flood basalt sequence of the Tachdamt Formation likely belongs to the ca. 885-883 Ma intraplate Iguerda-Taïfast Large Igneous Province (LIP) event defined by previously dated dykes in the Iguerda and Taïfast inliers; and 7) the 1650 Ma Zenaga LIP can be potentially linked with LIP magmatism in Baltica and Laurentia.

Melting of recycled carbonate in the mantle explains the origin of carbonatitic magmas., The origin of carbonatites—igneous rocks with more than 50% of carbonate minerals—and whether they originate from a primary mantle source or from recycling of surface materials are still debated. Calcium isotopes have the potential to resolve the origin of carbonatites, since marine carbonates are enriched in the lighter isotopes of Ca compared to the mantle. Here, we report the Ca isotopic compositions for 74 carbonatites and associated silicate rocks from continental and oceanic settings, spanning from 3 billion years ago to the present day, together with O and C isotopic ratios for 37 samples. Calcium-, Mg-, and Fe-rich carbonatites have isotopically lighter Ca than mantle-derived rocks such as basalts and fall within the range of isotopically light Ca from ancient marine carbonates. This signature reflects the composition of the source, which is isotopically light and is consistent with recycling of surface carbonate materials into the mantle.

The best preserved and most complete lava flow sequences of the Central Atlantic Magmatic Province (CAMP) in Morocco are exposed in the Central High Atlas and can reach up to 300 m in thickness. Four distinct formations, emplaced in subaerial environments, are classically recognized: the Lower, Intermediate, Upper and Recurrent formations. These formations are separated by paleosoils and sedimentary sequences (mudstones, siltstones, sandstones, limestones), that are in general less than two meter-thick and may exceptionally reach a thickness of 80 m, representing minor periods of volcanic quiescence. CAMP lava flows of the Central High Atlas can be grouped into two main categories: subaerial compound pahoehoe flows and simple flows. The former type is exclusively confined to the Lower and Intermediate Formations, while simple flows occur in the Upper and Recurrent Formations. The dominance of compound flows in the two lowermost units of the CAMP suggests a slow emplacement during successive sustained eruptive episodes. Instead the thick single flows characterizing the Upper and Recurrent units indicate higher effusive rates. Basaltic pillow lavas (always of short lateral extent: 10 to 100 m), showing radial jointing and vitreous rinds, identical to those found in the Western Meseta, are occasionally associated with hyaloclastites in the base of the Intermediate Formation, immediately above clastic sediments, or in the Upper Formation. The occurrence of pillow lavas does not imply a generalized subaqueous environment at the time of the lava emission. Instead, they represent subaerial flows that entered small lakes occupying depressions on the volcanic topography of the Lower and Intermediate Formations. The short lateral extent of the pillow lavas and their constant stratigraphic position, the existence of lava flows with unequivocal subaerial characteristics associated to sediments containing fossilized wood, clearly indicate onshore emplacement.

The occurrence of Lower Paleozoic mafic magmatic rocks in the Central Iberian Zone (CIZ) of the Variscan Orogen is rare. Amphibolites and metagabbros embedded in the metasediments of the Douro-Beiras Supergroup outcrop at Farminhao, Viseu (central-north Portugal). The protoliths of these two rock types are tholeiites presenting different isotopic signatures (eNd480 = +4.63 to +4.93 and +5.74 to +7.67) and incompatible element ratios (normalized La/Lu up to 4.5 and down to 0.7), respectively which suggests they are not cogenetic. The closely related meta-ultramafic rocks are considered as cumulates generated from the magmas that originated the metagabbros. The elemental and isotopic features of the metagabbros are similar to those reported for amphibolitic occurrences in Tenzuela (near Segovia, Spain) which allows the proposition of a similar age for the mafic rocks of Farminhao. Despite the depleted characteristics of the studied rocks, they are interpreted as having been formed during a continental rifting process characterized by variable degrees of stretching, some 100 Ma after the end of the deposition of the Douro-Beiras Supergroup. This rifting event marks the onset of the Variscan Cycle (s.l.) in the Central Iberian Zone. The occurrence of these metabasic rocks near the confluence between the Porto-Viseu Metamorphic Belt and the Juzbado-Penalva do Castelo Shear Zone suggests that these first-order structures may have worked as weakness zones constraining the ascent of magmas during the Ordovician. The Lower Ordovician metabasic rocks here studied are chemically similar to the abundant lower to medium Cambrian magmatic rocks of the Ossa Morena Zone, also in Iberia, further reinforcing the diachronous character of the opening of the Rheic Ocean that later propagated to the eastern sectors of the European Variscan Belt.

The Late Triassic-Early Jurassic volcanic sequence of the Central Atlantic Magmatic Province (CAMP) of Morocco is classically subdivided into four stratigraphic units: the Lower, Middle, Upper and Recurrent Formations separated by intercalated sediments deposited during short hiatuses in volcanic activity. Although corresponding to a Large Igneous Province formed in continental environment, it contains subaqueous lava flows, including dominant pillowed flows but also occasional sheet flows. We present a study of the morphology, structure and morphometry of subaqueous lava flows from three sections located at the Marrakech High-Atlas (regions of Ait-Ourir, Jbel Imzar and Oued Lhar-Herissane), as well as an analysis of the sediments, in order to characterize them and to understand their environmental meaning. The analysis of clays by the diffraction method X-ray revealed the presence of illite, mica, phengite, celadonite, talc and small amounts of quartz, hematite, calcite and feldspar, as well as two pairs of interbedded irregular (chlorite Smectite/chlorite-Mica). Fibrous minerals such as sepiolite and palygorskite were not detected. The peperite of Herissane region (Central High Atlas) provided an excellent overview on the factors favoring the magma-sediment interaction. These are the products of a mixture of unconsolidated or poorly consolidated sediments, low permeability with a low viscosity magma. The attempt of dating palynology proved unfortunately without results.

The crustal architecture of the Western Iberian Margin is investigated so that the relationship between synrift intra-plate segmentation, magmatic events and subsequent margin convergence can be discussed in the context of the evolution of the Central–North Atlantic Ocean. The evidence in this paper indicates distinct crustal architectures for NW Iberia (lower-plate) and SW Iberia (upper-plate), as shown by (1) the different geometries of the rotated tilt-blocks across thinned continental crust, (2) the distinct dips of deep crustal detachments and (3) the presence of first-order strike-slip zones bounding different crustal segments. We demonstrate that a switch in the dip direction of the crustal detachment is accomplished by accommodating persistent transcurrent deformation along first-order transfer zones and associated uplifted hinges, both of which accommodated synrift displacement and post-rift margin inversion. This alternating architecture explains why recurrent magmatism is conspicuously located on the upper-plate margin, which we consider to have favoured, in discrete pulses, the emplacement of magma. Finally, the crustal detachment underlying the upper-plate is interpreted to have been reactivated since the Eocene as the weak zone accommodating ocean–continent convergence and the putative onset of margin subduction. Supplementary material: Summary of the three main magmatic events on the onshore and offshore West Iberia and their associated occurrences, location and magmatism type, in relation with the syn- to post-rift evolution of the margin are available at https://doi.org/10.6084/m9.figshare.c.3591209

The oceanic basins are dotted by seamounts, guyots and islands formed by the mantle plumes and oceanic lithosphere interaction. These plumes are responsible for several intraplate volcanisms such as the Emperor-Hawaii Chain in the Pacific Ocean with a remarkable bend at ca. 47 Ma. Comparatively, the Vitoria-Trindade Ridge (VTR) in the South Atlantic Ocean was also generated by a mantle plume and in response to the lithosphere interaction and tectonic settings it shows three remarkable bends through time. One occurred after 85 Ma associated with the Trindade plume tail movement under the Archean Sao Francisco Craton, and another one ca. 52 Ma after the formation of the Abrolhos Bank in the Brazilian platform (Mohriak, 1989; Thompson et al., 1998) when the Trindade Plume encountered a thinner lithosphere in the Brazilian coast and formed a chain of seamounts and islands of W-E direction. The last bend marked in the Trindade plume trajectory is ca. 20°00′lat, around Davis Bank, marking a Miocene (21.07 Ma - 40Ar/39Ar whole-rock method) subtle clockwise rotation in the South American Plate. The easternmost part of this ridge is composed of Trindade-Martin Vaz Archipelago subject of this study. Located ca. 1200 km away from the Brazilian coastline at the Vitoria (ES) parallel, its geology is an important preserved record of an alkaline Pliocene-Pleistocene volcanism, the youngest one recorded in the Brazilian territory. Martin Vaz and the nearby islets are located on the easternmost part of the VTR. Its geological features include phono-tephritic to tephri-phonolitic domes; nosean-phonolitic dykes and sub-horizontal layers formed by pyroclastic rocks and subordinate lava flows (melanephelinites) of Volcanian-style magmatism (mostly). 40Ar/39Ar ages yielded values ranging from 336 to 721 ka representing a young and short period of intraplate magmatic activity in the South American Plate offshore. These new ages associated with compiled radioisotopic ages from onshore and offshore volcanic rocks represent a strong decreasing age correlation related to Trindade Mantle Plume. Moreover, Trindade-Martin Vaz Archipelago is a contemporaneous product of a terminal plume expression in the offshore portion of a long-lived track (ca. 90 Ma) with a slow shear velocity (VS) placing its origin at the Upper Mantle suggesting a shallow mantle plume rising from the asthenosphere.

International audience; The genesis and evolution of migmatite-granite terranes usually involve several complex petrological and geochemical processes that leave their imprint on elemental and isotopic signatures. In this paper, we assess the role of melting reactions on the genesis of the variscan Figueira de Castelo Rodrigo-Lumbrales Anatectic Complex (FCR-LAC) in the Central Iberian Zone that culminated in the generation of abundant S-type granites. At odds with the proposed for several anatectic complexes elsewhere, here we demonstrate that no isotopic (Sr-Nd-Hf-Pb) disequilibrium occurred in the FCR-LAC, either in the transitions from metatexites to diatexites nor to granites. However, variable contribution of the source minerals generated batches of melts characterized by distinct parent/daughter ratios, which explain the significant heterogeneity of present-day isotopic signatures. While Rb/Sr ratios and the Pb budget of the successively generated lithotypes were mainly controlled by major minerals such as muscovite, K-feldspar and plagioclase, the accessory phases played a major control on the Sm/Nd and Lu/Hf ratios. Our study also demonstrates the existence of two distinct diatexite groups produced by different melting reactions. Type-1 diatexites, having high Rb contents and fractionated HREE, are geochemically akin to the associated S-type granites. They were produced by dehydration-melting of muscovite with production of peritectic K-feldspar, sillimanite and melt. The less abundant type-2 diatexites required influx of external fluids for melting, which consumed more plagioclase than muscovite.Isotopic data reveal the existence of two groups with distinct initial compositions (εNd320 = −5.05 to −6.03 and εHf320 = −3.42 to −4.45 vs. εNd320 = −7.30 to −8.89 and εHf320 = −6.45 to −8.47), both composed of metatexites, diatexites and granites, due to source heterogeneity. The main source of the anatectic complex was the metasedimentary Neoproterozoic – lower Cambrian Douro-Beiras Supergroup, with minor contribution of Ordovician, Ollo de Sapo magmatic rocks.

We analysed the crystallography and the chemistry (major and trace elements) of 16 Cr-diopsides belonging to mantle xenoliths from northern (Waw-En-Namus, Libya; Bou-Ibalrhatene and Tafraoute, Morocco) and central Africa (Nyos and Barombi maars, Cameroon). These mantle xenoliths were extracted from mantle domains underlying a metacraton (Libya), a pericraton (Morocco), and a Pan-African mobile belt (Cameroon). The clinopyroxenes from pericratonic and mobile belt occurrences show similar geochemical features. They usually have high R3+ content and low Ca. When normalized to chondrite abundances, their incompatible trace elements show a wide spectrum of patterns, from slightly depleted to slightly enriched and U-shaped patterns. Such features may indicate interaction with carbonatitic and silicic melts. Their Vcell suggest different equilibrature pressures that are compatible with an ascending diapir and/or entrapment by magmas at different depths within the lithospheric mantle. It is important to stress that variable cell and tetrahedron volumes suggest that Libyan clinopyroxenes formed at variable depths. Those arising from shallower depth are less depleted and may display enriched and U-shaped patterns, while clinopyroxenes deriving from deeper zones display depleted and flat incompatible element patterns, possibly suggesting a melt extraction preceding the delamination of the SCLM.

The West and SouthWest Margins of Iberia started their formation as intra-continental rifts during initial break up of Pangea in Triassic times. The tectono-stratigraphic record of the Algarve, Alentejo and Lusitanian basins and their offshore prolongation documents the syn-rift, post-rift and passive margin phases of the rifting process as well as three magmatic cycles of tholeiite to alkaline affinities. Although the Ocean-Continent Transition has been investigated using deep ocean drilling, seismics, gravimetry and magnetics its nature and location are still matters of debate. The tectonic inheritance of the Paleozoic Orogeny had great influence in the geometry of the rift basins and development of the Neo-Tethys and Atlantic Oceans intersection. Salt tectonics strongly controlled both syn-rift and post-rift basin tectonics and led to the formation of an allochthonous salt nappe in the Algarve Basin.

19 pages, 7 figures, The Alpine orogeny is well recorded onshore and offshore by tectonic inversion of the Mesozoic rift basins. Large scale linear seamounts (more than 250 km long and with up to 5 km of uplift) involving oceanic and continental lithosphere were carried on top of thrusts, such as the Gorringe seamount and the Estremadura Spur in the SouthWest and West Iberia Margin, respectively. The SouthWest Iberia Margin also recorded the westward migration of the Gibraltar Oceanic slab as the westwards propagation of the Neo-Tethys subduction. Rotation of the tectonic compression from NW-SE to WNW-ESE in Pliocene times caused the development of large scale dextral wrench faults as the present day Africa-Iberia plate boundary. Neotectonics of this plate boundary caused large to mega-scale destructive earthquakes and tsunamis

The Salmas plutonic complex, in the northernmost part of Sanandaj-Sirjan Zone of Iran, provides evidence for magma interaction processes. The complex contains mafic-intermediate, hybrid and felsic rocks which intruded into the Paleozoic metamorphic complex. They show typical relationships described in many mafic–felsic mingling and mixing zones worldwide, such as mafic microgranular enclaves (in felsic and hybrid rocks), mafic sheets, and hybrid rocks. The mafic microgranular enclaves (MMEs) are characterized by fine-grained, equigranular and hypidiomorphic texture and some special types of microscopic textures, e.g., quartz xenocrysts, oscillatory-zoned plagioclase, small lath-shaped plagioclase in large plagioclase, spike zones in plagioclase and spongy-cellular plagioclase textures, rounded plagioclase megacrysts blade-shaped biotite, acicular apatite. The mafic sheets and MMEs in granites (MME-Gr), which indicated magma mingling structures, show ISr values and eNd(i) similar to diorites. The hybrid rocks and their mafic enclaves (MME-H) show isotope signatures similar to each other. Granites have isotope signatures [higher 87Sr/86Sr(i) (0.70788–0.71075) and lower eNd(i) (−2.4 to −4.2)] distinct to those of the all rock types and MMEs. Major, trace and REE modeling show that hybrid rocks are generated via 40–60% mixing of mafic (dioritic) and felsic (granitic) end-members. All the geochemical data suggest that underplating of dioritic magma, which has been produced by fractional crystallization of gabbros, under the lower crust caused its melting to make felsic (granitic) magma. Injection of dioritic magma into the base of the felsic magma chamber and a limited mixing of two end-members, the lower crust-derived magma and mantle-derived melts, formed hybrid magma and their enclaves. Injections of new mafic magma pulses into hybrid magma generated mafic enclaves into them. The injections of denser dioritic magma pulses into a felsic magma chamber and spreading of it at the level of rheological contrast have been formed mafic sheets and MMEs in granites.

Noble gas geochemistry is a valuable tool for assessing the nature of contributors to magma mantle sources. In this chapter, we analyse previously published data regarding helium and neon in the Azores to discuss the origin of the Azores archipelago. After the pioneering works of Kurz et al. (1982a, 1990) examining helium isotopic variations along the Mid-Atlantic Ridge (MAR) between 28°N and 53°N and on Sao Miguel Island, a systematic study was conducted by Moreira et al. (1999) on several Azores islands. These authors analysed He isotopic ratios from phenocrysts collected in five islands of the archipelago. Helium isotopic data from Terceira (minimum 4He/3He ratio of ≈63,700; R/Ra ≈11.3) were interpreted as the presence of a relatively primitive component in the mantle source, whereas the radiogenic 4He/3He ratios found at Sao Miguel (from 121,600 to 276,800; R/Ra from ≈5.9 to ≈2.6) have been interpreted as resulting from the melting of an enriched and ancient recycled material. Moreira and Allegre (2002) analysed noble gas isotopic data for MORB glasses dredged along a MAR segment (from 21.25°N to 39.9°N), which also includes the Azores triple junction area. The obtained 4He/3He ratios decrease from 90,000 at 37°N to 75,000 at 38.5°N and later increase to 100,000 at 40.5°N. The low 4He/3He ratio measured on the ridge at 38.5°N (76,000; R/Ra = 9.5) was interpreted as the result of present-day interaction between the ridge source and the Azores plume (see also Madureira et al. 2014), as sampled by lava erupted at Terceira and Sao Jorge islands (the latter with 4He/3He ratios down to 40,000; R/Ra ≈18). Madureira et al. (2005) focused their study on Terceira Island, for which He and Ne isotopic ratios were determined from olivine phenocrysts. Ne isotopic data corroborated the presence of a relatively primitive component in the Terceira mantle source (21Ne/22Necorr = 0.052), which is, however, dominated by a MORB-type component. Jean-Baptiste et al. (2009) presented helium isotope data for thermal waters and gas emissions sampled at Terceira, Graciosa and Sao Miguel islands, as well as Faial, Pico and Flores islands. The results were interpreted as the presence of relatively primitive He isotopic ratios at Terceira (4He/3He ≈53,500; R/Ra ≈13.5), which also extend to Graciosa Island (4He/3He ≈64,500; R/Ra ≈11.2). These values contrast with those obtained by these authors for Sao Miguel Island, which are significantly more radiogenic than those typical of MORB (4He/3He from ≈120,400 to ≈138,900; R/Ra from 5.2 to 6.0) and are in agreement with the helium measurements in lavas from the eastern part of Sao Miguel (Moreira et al. 2012). Noble gas geochemistry suggests, despite the strong dilution of its primitive signature by MORB-like material, that a lower mantle-derived mantle plume is located under the central group of islands, particularly under Sao Jorge, in agreement with seismic tomographic images. The peculiar helium isotopic ratios observed in Sao Miguel lavas can be explained by different scenarios invoked for the Sr–Pb isotopic and trace element systematics, which suggest that the Sao Miguel source contains recycled mafic material ~3 Ga in age (e.g., Beier et al. 2007; Elliott et al. 2007).

Recent evidence suggests that a portion of the Canary plume travelled northeastwards below the lithosphere of the Atlas Mountains in North Africa towards the Alboran domain and was captured ∼10 Ma ago by the Gibraltar subduction system in the Western Mediterranean. The capture would have been associated with the mantle return flow induced by the westward-retreating slab that would have dragged and trapped a portion of the plume material in the mantle wedge of the Gibraltar subduction zone. Such material eventually contaminated the subduction related volcanism in the Alboran region. In this work, we use scaled analogue models of slab–plume interaction to investigate the plausibility of the plume capture. An upper-mantle-scaled model combines a narrow (400 km) edge-fixed subduction plate with a laterally offset compositional plume. The subduction dominated by slab rollback and toroidal mantle flow is seen to increasingly impact on the plume dynamics as the area of influence of the toroidal flow cells at the surface is up to 500 × 1350 km2. While the plume head initially spreads axisymmetrically, it starts being distorted parallel to the plate in the direction of the trench as the slab trench approaches the plume edge at a separation distance of about 500 km, before getting dragged towards mantle wedge. When applied to the Canary plume–Gibraltar subduction system, our model supports the observationally based conceptual model that mantle plume material may have been dragged towards the mantle wedge by slab rollback-induced toroidal mantle flow. Using a scaling argument for the spreading of a gravity current within a channel, we also show that more than 1500 km of plume propagation in the sublithospheric Atlas corridor is dynamically plausible.

Recurrent eruptions at very active ocean island volcanoes provide the ideal means to gain insight on the scale of spatial variations at the mantle source and on temporal changes of magma genesis and evolution processes. In 2014, after 19 years of quiescence, Fogo volcano (Cape Verde Archipelago) experienced a new eruption, with the vents located 200 m from those of the 1995 eruption, and less than 2000 m from those of the 1951 event. This offered a unique opportunity to investigate the existence of small-scale mantle heterogeneities and the short-term compositional evolution of magmas erupted by a very active oceanic volcano like Fogo. Here we present petrological and geochemical data from the early stages of the Fogo's most recent eruption - started on November 23, 2014 - and compare them with the signature of previous eruptions (particularly those of 1995 and 1951). The magmas erupted in 2014 are alkaline (up to 23.4% and 0.94% of normative ne and lc, respectively) with somewhat evolved compositions (Mg # < 56), ranging from tephrites to phonotephrites. The eruption of phonotephritic lavas preceded the effusion of tephritic ones. Lavas carried to the surface clinopyroxene and kaersutite phenocrysts and cognate megacrysts, which indicate that the main stages of magma evolution occurred in magma chambers most probably located at mantle depths (25.6 5.5 km below sea level). This was followed by a shallower (

Cape Verde is an intraplate archipelago located in the Atlantic Ocean about 560 km west of Senegal, on an ∼ 130 Ma old oceanic lithosphere. The upper-mantle structure beneath the islands was poorly known, until recently, in large part due to the lack of broadband seismic stations. In this study we used data from two temporary deployments across the archipelago, measuring the phase velocities of Rayleigh-waves fundamental-modes in a broad period range (8–250 s), by cross-correlating teleseismic earthquake data between pairs of stations. We derived a robust average, phase-velocity curve for the Cape Verde region, and inverted it for a shear-wave velocity profile. Our results show significantly low velocities of ∼ 4.2 km/s in the asthenosphere, indicating the presence of anomalously high temperatures and, eventually, partial melting. The temperature anomaly is probably responsible for the thermal rejuvenation of the lithosphere to an effective age as young as about 30 Ma, which we infer from the comparison of seismic velocities beneath Cape Verde archipelago and those representative of different ages in the Central Atlantic. The anomalously high temperature in the asthenosphere, together with previously published evidence on low seismic velocities in the lower mantle and relatively He-unradiogenic isotopic ratios, suggests a hot plume, rooted deep in the lower mantle, as the origin of the Cape Verde hotspot.

New geochemical, isotopic (Sr-Nd-Hf-Pb) and K-Ar data, are presented here on samples from the Southern Azores Seamount Chain (SASC) located south of the Azores Plateau. The SASC also includes the Great Meteor, Small Meteor and Closs seamounts, morphologically connected by a saddle at − 4100 m deep. We conclude that the SASC are characterized by a narrow isotopic variability that falls within the Azores isotopic field. Although each seamount has its own isotopic signature, their mantle source must comprise four local mantle end-members, three of which are common to the Azores, e.g. Plato isotopic signature results from the mixing between HIMU and N-MORB while Great Meteor signature results from this mix with the Azores Common Component (AzCC). A fourth end-member with high 208Pb/204Pb and decoupled Th/U ratios (Δ8/4 up to 59.2) is identified on Great Meteor northern flank. New K-Ar ages on Plato (33.4 ± 0.5 Ma) and Small Hyeres (31.6 ± 0.4 Ma) show nearly coeval volcanism, which is contemporaneous with the E-MORBs erupted at the MAR, drilled on oceanic crust with 30-34 Ma (DSDP82). This study endorses the genetic link between the Azores Archipelago and the SASC to the long-term activity of the Azores plume and the large-scale ridge-hotspot interaction, contributing to better constrain the temporal-spatial evolution of this region of the North Atlantic.