Littérature scientifique sur le sujet « Intraplate magmatism »

Geochemical and isotope-geochronological evidence of the manifestation of Late Riphean intraplate magmatism within the Chernorechensky massif at the western margin of the Siberian craton were obtained. These rocks crystallized from high-temperature and anhydrous (water unsaturated) magmas with high concentrations of alkalis, iron, and, mostly incompatible elements, which is typical for anorogenic A-type granites in intraplate extension setting. Their U-Pb zircon age 723 ± 6 Ma can be correlated with the Franklin rift event widely manifested in the north of Laurentia, associated with the breakup of Rodinia. The synchronous successions and similar style of magmatic activity and concomitant rifting, as well as a similar sequence of tectonic-thermal events along the Arctic margin of Rodinia support the spatial proximity of Siberia and the North Atlantic cratons at this time as proposed for the paleogeographic reconstructions.

Isostasy, flexure and dynamic processes all influence the shape of the Earth’s surface. While the first two processes are well understood, dynamic topography remains controversial. On the continents, dynamic uplift is often expressed by positive long-wavelength gravity anomalies, radial drainage patterns, and slow seismic velocity anomalies within the upper mantle. Volcanic activity and elevated heat flow are also often observed. The aim of this study is to investigate the link between geochemical compositions of intracontinental magmatism and geophysical, geomorphological and geodetic observations of dynamic uplift. Three volcanic regions are considered in detail: western North America, northeast Brazil and Madagascar. The combined database includes 348 new whole-rock geochemical analyses. Rare earth element concentrations of mafic, asthenospheric-derived volcanic samples are exploited to calculate the depth and temperature of melt generation by inverse modelling. A sensitivity test of this modelling scheme is carried out. Lithospheric thickness and mantle temperature are independently determined from shear wave velocity models. Beneath western North America, a negative correlation between shear wave velocities at depths of 70–150 km and degree of melting is observed. Temperatures obtained from igneous compositions and from shear wave velocity profiles beneath volcanic fields closely agree. Melts are produced within, or close to, the spinel-garnet transition zone at depths shallower than $\sim$70 km, yielding mantle potential temperatures of up to 1380$^{\circ}$C. Calculated uplift and heat flow based upon these results match observed surface elevation and heat flow measurements. In northeast Brazil, Jurassic, Cretaceous and Cenozoic phases of mafic igneous activity are recognised. Jurassic magmatic activity probably resulted from spinel-field melting at potential temperatures of $\sim$1380$^{\circ}$C. This episode is associated with regional magmatism during break-up of the Central Atlantic Ocean. Cretaceous compositions record melting at potential temperatures of 1330–70$^{\circ}$C at similar depths. This activity is linked to extension at the time of break-up of the equatorial and South Atlantic Ocean. Cenozoic volcanism comprises low-degree melts within the spinel-garnet transition zone at ambient potential temperature. Shear wave velocity models support these results. Cenozoic volcanism in Madagascar is predominantly alkaline and records small-degree melting with minor temperature anomalies within the spinel-garnet transition zone. Rare tholeiitic basalts record temperatures up to 1360$^{\circ}$C. Analysis of global and regional shear wave velocity models closely matches these results. The principal control on continental magmatism appears to be temperature anomalies within the upper mantle beneath thin lithosphere. Highest mantle potential temperatures correlate with largest dynamic uplift. Mantle potential temperatures $ < $1350$^{\circ}$C are matched with minimal or negative dynamic topography.

Intraplate magmatism provides important constraints on the evolution, dynamics and composition of the Earth's mantle. Uncertainties remain, however, in understanding the mantle sources related to intraplate magmatism. For example, the influence or existence of mantle stratification, core-mantle interaction and recycling of subducted components are poorly understood. The extent to which geochemical signatures of intraplate magmas are modified during melt transportation, eruption and emplacement also requires better definition. This thesis employs He, O and Re-Os isotope systematics on selected volcanic and intrusive rocks from a number of oceanic and continental intraplate settings to address some of these key issues. New constraints on the effect of syn-eruptive degassing and post-emplacement mobility processes on intraplate magmas are presented. Ocean Island Basalts (OIB) from the Western Canary Islands and Coppermine Continental Flood Basalts (CFB) suggest that Re degassing for both modem and ancient alkaline and tholeiitic sub-aerially empted lavas are similar in extent. Crustal contamination is shown to explain some low δ(^18)O (≤5%(_0) in central Icelandic lavas and low (^3)He/'(^4)He (<8R(_A)) in Western Canary Island and central Iceland lavas. Study of the Mackenzie large igneous province (LIP) also reveals that relatively limited (2-4%) crustal contamination can generate large (^187)Os/(^188)Os isotopic variation (≥80 γOs units) in high Os concentration cumulate rocks. This finding provides direct support for the role of crustal contamination in the formation of stratiform chromitite reefs in the Muskox Intrusion. By inference, contamination by ancient (≥0.5Ga) continental crust might also explain coupled (^186)Os-(^187)Os enrichments in some continental intraplate magmas. He isotope ratios of intraplate magmas have been used to infer mantle stratification with both shallow and deep mande origins proposed for a long-lived, primordial, high (^3)He/(^4)He reservoir. In this work the continental lithospheric mantle, especially Archaean peridotite and eclogite, are shown to possess low (^3)He/(^4)He (<4R(_A)). This observation, combined with low (^3)He/(^4)He (6±1R(_A)) of continental intraplate alkaline volcanics (CIAV), derived from the lithosphere-asthenosphere boundary, provides evidence that a long-lived primordial He component does not exist in the shallow upper mantle. Low δ(^18)O (< 0.9%(_0)) and high (^187)Os/(^188)Os (γOs = +8 to +37) for high Os concentration (> 50 ppt) Western Canary OIB indicate that recycled oceanic crust forms part of the mantle source for these basalts, a theme also common to low δ(^18)O measured in central Icelandic glasses with (^3)He/(^4)He ratios similar to those of mid ocean ridge basalts. Decoupling of lithophile (Sr, Nd, Pb) and siderophile (Os) isotope tracers from He in both settings provides evidence for (^3)He-recharge with (^3)He/(^4)He up to 11.8R(_A) for the Western Canary Islands and 34.3R(_A) for central Icelandic lavas. There is evidence in Western Canary Island lavas, and in OIB globally, that a common or 'universal' mantle component is present with a near-chondritic (^187)Os/(^188)Os (≥0.127), mantle-like δ(^18)O (~5.2%(_0)) and elevated (^206)Pb/(^204)Pb (≥19.1) with respect to the depleted mantle; the so-called FOZO (Focus Zone), PHEM (Primary He mantle), or C (Common) components. Coppermine Re-Os isochron ages (1284 ± 13 Ma) are within error of the accepted 1270 ± 4 Ma U-Pb age for the Muskox Intrusion. γOs initials derived from both the Coppermine CFB (+2.0) and Muskox Intmsion (+1.3) lie on an enstatite or ordinary chondritic Os isotopic evolution curve for the Earth's mantle indicating derivation from a source similar to the universal component recognised in modem-day OIB. These results can be interpreted in the context of a veined or banded peridotite-pyroxenite mantle. Small amounts of partial melting of a heterogeneous mantle source leads to great isotopic variability whilst larger degrees of partial melting will lead to more homogeneous mantle-derived compositions. Pyroxenite sources might also explain the correlated isotopic and elemental compositions, including the possibility of (^186)Os-(^187)Os enrichment in OIB through high Re/Os and Pt/Os ratios. Ultimately, a universal mantle component appears to be present in all intraplate magmatism. This universal component is not always related to high (^3)He/(^4)He and appears to provide an endmember component to all intraplate mantle melting signatures from the Archaean to the present-day.

La Grande-Comore est la plus grande île d'un archipel localisé dans le canal de Mozambique sur une croûte dont la littérature permet de suggérer une nature océanique. Le Karthala est le principal volcan bouclier de l'île, il est le seul dont on connaisse l'activité historique, qui se localise essentiellement le long de deux rifts zones et à leur intersection dans la caldeira sommitale. Un volcanisme ancien forme le massif du Badiner situé à son extrémité sud. Le faible degré de sous-saturation en silice et les compositions de ses laves nous indiquent qu'elles sont essentiellement le produit d'un degré de fusion partielle identique affectant une source unique ou le phlogopite et le grenat sont plus ou moins résiduels. Un modèle géophysique basé sur les taux de production magmatique des panaches mantelliques, ainsi que l'utilisation de résultats expérimentaux à hautes pressions, confirment une pression de fusion partielle élevée comprise entre 24 et 33 kbar. Les laves faiblement alcalines à transitionnelles des différents stades d'édification du Karthala ont des paragenèses variées : basaltes à olivine, océanites, ankaramites et basaltes à phénocristaux de plagioclase, qui témoignent de la diversité des processus de différenciation en jeu. L'évolution des compositions de ces laves nous a permis de mettre en évidence l'existence de deux chambres magmatiques distinctes. L'une profonde localisée à une profondeur d'environ 30 km (10 kbar), ou les liquides basaltiques subissent un fractionnement wehrlitique plus ou moins important à l'origine d'un enrichissement précoce en incompatibles. L'autre plus superficielle, localisée à la base de l'édifice volcanique, ou des fractionnements principalement océanitique et clinopyroxénitique, ainsi que gabbroïque à moindre échelle, ne leur font atteindre qu'un faible stade de différenciation (hawaiites et trachy-basaltes). (Doc Thèses)

La Grande-Comore est la plus grande île d'un archipel localisé dans le canal de Mozambique sur une croûte dont la littérature permet de suggérer une nature océanique. Le Karthala est le principal volcan bouclier de l'île, il est le seul dont on connaisse l'activité historique, qui se localise essentiellement le long de deux rifts zones et à leur intersection dans la caldeira sommitale. Un volcanisme ancien forme le massif du Badjini situé à son extrémité sud. Le faible degré de sous-saturation en silice et les compositions de ses laves nous indiquent qu'elles sont essentiellement le produit d'un degré de fusion partielle identique affectant une source unique où le phlogopite et le grenat sont plus ou moins résiduels. Un modèle géophysique basé sur les taux de production magmatique des panaches mantelliques, ainsi que l'utilisation de résultats expérimentaux à hautes pressions, confirment une pression de fusion partielle élevée comprise entre 24 et 33 kbar. Les laves faiblement alcalines à transitionnelles des différents stades d'édification du Karthala ont des paragenèses variées : basaltes à olivine, océanites, ankaramites et basaltes à phénocristaux de plagioclase, qui témoignent de la diversité des processus de différenciation en jeu. L'évolution des compositions de ces laves nous a permis de mettre en évidence l'existence de deux chambres magmatiques distinctes. L'une profonde localisée à une profondeur d'environ 30 km (10 kbar), où les liquides basaltiques subissent un fractionnement wehrlitique plus ou moins important à l'origine d'un enrichissement précoce en incompatibles. L'autre plus superficielle, localisée à la base de l'édifice volcanique, où des fractionnements principalement océanitique et clinopyroxénitique, ainsi que gabbroïque à moindre échelle, ne leur font atteindre qu'un faible stade de différenciation (hawaiites et trachy-basaltes).

Le stratovolcan des Mont Dore (massif central français) est caractérisé par l'existence d'une caldera, par l'abondance des laves de composition globalement intermédiaire trachyandesitique et par la coexistence de laves sur- et sous-saturées. Il s'est édifié en deux temps. De 3 a 1;5 ma, l'activité se concentre au niveau des volcans septentrionnaux (Mont Dore s. S. , d'ordanche, aiguiller). Cette période est marquée par l'effondrement de la caldera de la haute-Dordogne et l'émission de rhyolites (ponces rhyolitiques de la grande nappe, dôme de la Gacherie. . . ). De 0;9 a 0;25 ma, le volcan du Sancy puis le massif adventif s'édifient au sud des structures précedentes. L'étude géochimique (isotopes du sr, du nd et de l'oxygène associes aux éléments en trace) des basaltes s. L. Met en évidence une évolution par cristallisation fractionnée d'olivine et de clinopyroxenes (+ ou - opaques) depuis les basanites jusqu'aux hawaiites. Les laves trachyandesitiques hétérogènes sont marquées par des déséquilibres minéralogiques, des phénomènes complexes de brassage mécanique de magmas, associés à l'assimilation de xenocristaux, de cumulats, de roches subvolcaniques et de socle. L'expulsion de fluides et des liquides résiduels lors de la cristallisation plus ou moins rapide des inclusions comagmatiques basiques et postérieurement à leur incorporation dans un magma trachytisque joue un rôle important dans la genèse d'inclusions particulières, préalablement interprérees comme des "liquides fractionnés". Au vu des données isotopiques, les trachyandesites basiques ne peuvent être le résultat d'un simple mélange abouti entre deux magmas. L'abondance des trachyandesites ne serait qu'un artefact dû aux processus de brassage mécanique de magmas de realimentation périodique des réservoirs magmatiques. Les données isotopiques sur les ponces et dômes rhyolitiques (**(87)sr/**(86)sr et **(143)nd/**(144)nd) excluent une origine par anatexie généralisée de la croute granitique mais montrent l'existence d'une contamination par la croute granito-gneissique. Les trachyphonolites et phonolites sont issus de la cristallisation fractionnée d'amphibole, de sphène et de feldspath potassique a partir des basanites et tephrites. Un modèle évolutif de réservoir magmatique dans la croute supérieure est proposé en fonction de l'âge, de la nature et de la répartition spatiale des produits émis en surface. A partir de quelques données géochimiques sur les peridotites et les basaltes du massif central et des données géophysiques disponibles, des esquisses de manteau sous cette région volcanisée sont également proposées

Les produits des magmatismes permo-stéphaniens s'organisent soit en séries différenciées d'origine mantellique soit en séries acides d'origine crustale, ils sont d'affinité calco-calcaire à sub-alcaline potassique, ils sont associés généralement aux bassins intracrustaux tardi-varisque et ont certainement joué un rôle important dans la génèse et la mise en place des volcanismes étudiés. Des processus interactifs entre la croûte et le manteau sont responsables de l'enrichissement de la source magmatique en élèments incompatibles

Au jurassique, le Haut Atlas a été le siège d'une grande manifestation magmatique de nature alcaline. Elle a eu lieu en régime intraplaque contemporain à l'ouverture de l'Atlantique. Parmi ce cortège, les intrusions de Tirrhist et d'Anefgou s'organisent en une association de roches magmatiques basiques mises en place sous forme de plutons, dykes et de filons dans une série de sédiments marno-calcaires du Jurassique Moyen (bajocien et bathonien). L'étude pétrographique, minéralogique et géochimique des deux intrusions a mis en évidence trois groupes de roches: des facies gabbroïques, avec une faible variation minéralogique, représentés par des melatroctolites, des gabbros à olivine, des gabbros à biotite, des leucogabbros et des gabbros différenciés. Des facies dioritiques. Des facies synetiques albitisés, ou la phase minérale ferromagnésienne est presque inexistante. La caractérisation géochimique a permis de conclure que: la différenciation des roches étudiées est contrôlée par le phénomène de la cristallisation fractionnée. L'olivine, le plagioclase, le clinopyroxène, l'ammphibole et la biotite ont probablement joue le rôle le plus important. Les gabbros et les diorites constituent une évolution continue, alors que les syénites sont issues de la différenciation de magmas moins évolués qui ont donne les cumulats gabbroïques. Les roches basiques des deux intrusions résulteraient de la fusion faible d'un manteau appauvri en éléments immobiles, enrichi en éléments mobiles par des fluides d'origine profonde. Les deux intrusions se sont mises en place à la faveur d'anciennes fractures profondes réactivées

Tese de Mestrado em Geologia (Geoquímica, Mineralogia e Petrologia), 2021, Universidade de Lisboa, Faculdade de Ciências
Prolongando-se por ≈1000 km, ao longo das margens ocidentais de Portugal e Marrocos, a Crista Madeira-Tore (CMT) representa um dos principais elementos morfológicos da bacia do Atlântico Central Norte (ACN). Em toda a sua extensão, esta elevação assísmica submarina encontra-se isostaticamente compensada (tanto a nível regional como local) e coincide aproximadamente com a anomalia magnética J, o que permite pressupor, para a mesma, uma idade de ≈125-130 Ma. Dada a simetria entre a CMT e a Crista Assísmica J (CAJ), situada a sudeste dos Grand Banks (Terra Nova, Canadá), ambas as estruturas são consideradas conjugadas (sistema conjugado CAJ-CMT), depreendendo-se a sua formação contemporânea, na crista média atlântica, durante um período de elevada produtividade de magmas (desencadeado pela focalização de uma pluma mantélica), e subsequente separação em dois ramos pelo alastramento oceânico. Sobrepostos sobre o flanco este da CMT existem atualmente vários montes submarinos, estes apresentando idades entre os 102.8 e os 0.5 Ma. Tais datações comprovam a edificação destas ocorrências por um evento magmático distinto daquele que gerou a crista assísmica subjacente. Efetivamente, esta ilação é suportada pela natureza OIA (i.e., basaltos oceânicos alcalinos) rica em elementos incompatíveis destes edifícios vulcânicos, a qual difere da afinidade MORB (i.e., basaltos das cristas médias oceânicas) interpretada para a CMT a partir de uma sondagem realizada na CAJ. Assim sendo, a origem do magmatismo pós-rifting desta província foi atribuída à presença de uma grande anomalia de fusão mantélica sob o ACN (à profundidade de ≈660 km), tendo esta emitido diversos pulsos magmáticos desde o Cretácico Inferior, cuja distribuição espacial, na margem este atlântica, se encontra controlada pelas diferentes fases de movimentação da microplaca ibérica. No presente trabalho efetua-se a análise petrográfica, química mineral e geoquímica elementar e isotópica (isótopos de Sr, Nd, Hf e Pb) das litologias recuperadas pelo ROV Luso nos montes submarinos Rugoso (37.03°N, 14.25°W), Jo Cousin (36.07°N, 15.35°W) e Pico Pia (36.98°N, 13.82°W), pertencentes ao alinhamento vulcânico da CMT, no âmbito da campanha oceanográfica EMEPC/PEPC/Luso/2012. O Pico Pia foi já estudado no passado, tendo sido datado em 0.5 Ma. Contrariamente, o Rugoso e o Jo Cousin foram nomeados e amostrados pela primeira vez durante a referida expedição, representando o seu estudo uma contribuição inédita para o aumento do conhecimento acerca do magmatismo desta província ígnea. À semelhança dos edifícios vulcânicos da CMT antecedentemente reportados por outros autores, também o Rugoso, Jo Cousin e Pico Pia são edificados por magmatismo OIA. Destes, o Pico Pia comporta as amostras mais primitivas, correspondentes a melanefelinitos (SiO2 = 41.1-41.3 wt%), enquanto o Rugoso manifesta os exemplares lávicos mais evoluídos, nomeadamente nefelinitos s.s. (SiO2 = 50.7 wt%) e fonólitos (SiO2 = 56.0-56.7 wt%). Por seu turno, o Jo Cousin compreende as litologias de quimismo intermédio, referentes a basaltos alcalinos (SiO2 = 45.8-46.6 wt%). Todas as rochas analisadas são subsaturadas em SiO2 (possuindo nefelina normativa até 32.4% e leucite normativa até 9.3%) e, como é típico dos magmas OIA, todas se demonstram ricas em elementos incompatíveis. Dos três montes submarinos, o Jo Cousin apresenta a menor fracionação de REE ((La/Lu)N = 15.15-17.78), coadunável com a génese dos seus magmas a partir de uma maior percentagem de fusão parcial da fonte mantélica (até 22.5%). Em oposição, o Rugoso e o Pico Pia exibem a maior fracionação de REE ((La/Lu)N = 47.88 e 31.89-40.05, respetivamente), esta sendo conciliável com a geração dos seus magmas mediante uma menor percentagem de fusão da fonte mantélica (até 6.4% no Pico Pia). Dadas as suas propriedades elementares (e.g., elevadas razões LREE/HREE e (Tb/Yb)N, assim como DZr < DHf < 1), os líquidos magmáticos estudados foram originados pela fusão de um reservatório mantélico portador de granada magnesiana residual, de natureza lherzolítica. Neste sentido, nos três locais infere-se a ocorrência de magmatogénese a profundidade superior a 75 km. As razões isotópicas de Sr, Nd, Hf e Pb das amostras analisadas comprovam a existência de cogeneticidade intravulcão. No entanto, constata-se que diferentes montes submarinos registam assinaturas distintas, estas variando sistematicamente com a localização geográfica. Em particular, sublinha-se o facto de os dados isotópicos adquiridos expandirem o espetro composicional do magmatismo pós-rifting da CMT. Com efeito, enquadrando-se no setor central deste alinhamento vulcânico, o Rugoso e o Pico Pia denotam as maiores razões 87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb e 208Pb/204Pb e as menores razões 143Nd/144Nd e 176Hf/177Hf, as quais testemunham o menor empobrecimento integrado no tempo em elementos incompatíveis presentemente conhecido nesta região. Em contrapartida, situando-se no setor sul desta província ígnea, o Jo Cousin evidencia as maiores razões 143Nd/144Nd e 176Hf/177Hf e as menores razões 87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb e 208Pb/204Pb, estas denunciando o maior empobrecimento integrado no tempo em elementos incompatíveis à data observado neste território. Assim como o restante magmatismo pós-rifting da CMT, também o Rugoso, Jo Cousin e Pico Pia revelam propriedades isotópicas indicadoras da contribuição do componente mantélico HIMU (e.g., 206Pb/204Pb até 20.256), este sendo igualmente apontado pelas baixas razões LILE/HFSE das litologias mais primitivas (e.g., Rb/Nb = 0.26-0.57) e pelas suas razões (Nb/La)N geralmente superiores a 1 (0.90-1.67). Destaca-se a similaridade das assinaturas isotópicas das lavas do Rugoso e Pico Pia, o que permite determinar, para ambos estes vulcões, a mesma fonte mantélica. As assinaturas isotópicas das amostras do Rugoso e Pico Pia são idênticas às que caracterizam o Arquipélago das Canárias, ao passo que as do Jo Cousin se relacionam com as do Arquipélago da Madeira. Tais composições sugerem a presença, na margem este atlântica, de múltiplas ascensões mantélicas (mantle upwellings) efémeras, quimicamente semelhantes às das plumas alimentadoras destas províncias. As lavas colhidas no monte submarino Rugoso conservam diversas evidências petrográficas e de química mineral que anunciam a ocorrência de fenómenos de mistura de magmas neste local. Em primeira instância, os mesmos são apontados pelos zonamentos composicionais inversos dos fenocristais e microfenocristais de clinopiroxena dos nefelinitos s.s., estes assinalando a recarga da câmara magmática deste vulcão por líquidos mais primitivos após a cristalização do núcleo destes minerais. Tendo em conta as suas características elementares e isotópicas, a atividade ígnea dos montes submarinos Rugoso, Jo Cousin e Pico Pia integrar-se-á, muito provavelmente, na sexta etapa de magmatismo pós-rifting (32-0 Ma) individualizada na margem este do ACN. Em virtude da convergência África-Eurásia, entre o Oligocénico e a atualidade, o vulcanismo nesta região está confinado à placa africana, somente possuindo expressão na proximidade dos ramos central e sul da Zona de Fratura Açores-Gibraltar.
Extending for ≈1000 km, along the western margins of Portugal and Morocco, Madeira-Tore Rise (MTR) is one of the main morphological elements of the North-Central Atlantic (NCA) basin. Throughout its length, this submarine aseismic elevation occurs isostatically compensated (both regionally and locally) and approximately coincides with the J magnetic anomaly, which allows to interpret, for the same, an age of ≈125-130 Ma. Given the symmetry between MTR and J Anomaly Ridge (JAR), located to the southeast of the Grand Banks (Newfoundland, Canada), both of these structures are considered conjugates (MTR-JAR conjugate system), having been contemporaneously formed, in the mid-Atlantic ridge, during a period of high magma productivity (triggered by the focus of a mantle plume), and later separated into two branches by the oceanic spread. Superimposed on the eastern flank of the MTR there are currently numerous seamounts, with ages ranging between 102.8 and 0.5 Ma. Such geochronological data attest the construction of these occurrences by a magmatic event different from the one that generated the underlying aseismic elevation. In fact, this conclusion is supported by the OIA (i.e., ocean island alkaline basalts) and incompatible elements-rich nature of these volcanic buildings, differing from the MORB (i.e., mid ocean ridge basalts) affinity inferred for MTR from a borehole carried out in JAR. Consequently, the origin of the post-rifting magmatism of this province was attributed to the presence of a large-scale mantle melting anomaly under NCA (at a depth of ≈660 km), this having emitted several magmatic pulses since the Lower Cretaceous, whose spatial distribution on the eastern Atlantic margin is controlled by the different motion phases of the Iberian microplate. In this work, petrographic, mineral chemistry, elemental and isotopic (Sr, Nd, Hf and Pb isotopes) analyses were performed on samples collected by the ROV Luso in Rugoso (37.03°N, 14.25°W), Jo Cousin (36.07°N, 15.35°W) and Pico Pia (36.98°N, 13.82°W) seamounts, belonging to the MTR volcanic alignment, during the EMEPC/PEPC/Luso/2012 oceanographic campaign. Pico Pia was studied in the past, being dated at 0.5 Ma. In contrast, Rugoso and Jo Cousin were both named and sampled for the first time in the referred expedition, their study representing an unprecedented contribution to increasing the knowledge about the magmatism of this igneous province. Like all the MTR volcanic buildings previously reported by other authors, Rugoso, Jo Cousin and Pico Pia are also formed by OIA-type magmatism. Of these, Pico Pia contains the most primitive samples, corresponding to melanephelinites (SiO2 = 41.1-41.3 wt%), while Rugoso includes the most evolved rocks, namely nephelinites s.s. (SiO2 = 50.7 wt%) and phonolites (SiO2 = 56.0-56.7 wt%). On the other hand, Jo Cousin has the lithologies of intermediate composition, referring to alkali basalts (SiO2 = 45.8- 46.6 wt%). All of the analyzed lavas are highly SiO2-undersaturated (having normative nepheline up to 32.4% and normative leucite up to 9.3%), and, as it is typical of OIA magmas, all of them are enriched in incompatible elements. Of the three seamounts, Jo Cousin depicts the lowest fractionation of REE ((La/Lu)N = 15.15-17.78), consistent with the generation of its magmas through a higher melting percentage of the mantle source (up to 22.5%). Contrarily, Rugoso and Pico Pia exhibit the greatest fractionation of REE ((La/Lu)N = 47.88 and 31.89-40.05, respectively), which is consistent with the genesis of their magmas by a lower melting degree of the mantle source (up to 6.4% in Pico Pia). Considering their elemental properties (e.g., high LREE/HREE and (Tb/Yb)N, DZr < DHf < 1), the studied magmatic liquids were originated by partial melting of a mantle reservoir with residual magnesian garnet, presumably of lherzolitic nature. Therefore, in these three volcanoes, magmatogenesis is estimated to have occurred at depths greater than 75 km. Sr, Nd, Hf and Pb isotope ratios of the analyzed samples testify the existence of intravolcano cogeneticity. However, different seamounts depict distinct isotopic signatures, these varying systematically with geographic location. In particular, the acquired data expands the compositional spectrum of the post-rifting magmatism of MTR. Occurring in the central sector of this volcanic alignment, Rugoso and Pico Pia display the highest 87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios and the lowest 143Nd/144Nd and 176Hf/177Hf ratios, showing the lowest time-integrated depletion in incompatible elements of the mantle source presently recognized in this region. On the other hand, located in the southern sector of this igneous province, Jo Cousin has the highest 143Nd/144Nd and 176Hf/177Hf ratios and the lowest 87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios, these concerning to the greater time-integrated depletion in incompatible elements of the mantle source hitherto observed in this territory. Equivalently to other MTR post-rifting occurrences, Rugoso, Jo Cousin and Pico Pia also reveal isotopic properties indicating the contribution of the HIMU mantle component (e.g., 206Pb/204Pb up to 20.256), this also being supported by the low LILE/HFSE ratios of the most primitive samples (e.g., Rb/Nb = 0.26-0.57) and their (Nb/La)N ratios mostly higher than 1 (0.90-1.67). Moreover, Rugoso and Pico Pia denote similar isotopic signatures, which allows to infer, for both of these seamounts, the same mantle source. Rugoso and Pico Pia isotopic signatures are compatible with those that characterize the Canary Archipelago, while those of Jo Cousin are identical to those of the Madeira Archipelago. Such compositions suggest the presence, on the eastern Atlantic margin, of multiple ephemeral mantle upwellings, chemically similar to those of the plumes feeding these provinces. Lithologies recovered in seamount Rugoso include several petrographic and mineral chemistry evidences for the occurrence of magma mixing phenomena in this location. These are essentially shown by the reverse compositional zoning of clinopyroxene phenocrysts and microphenocrysts of the nephelinites s.s., implying the recharge of the magmatic chamber of this volcano by more primitive liquids after the crystallization of the central portion of these minerals. Considering their elementary and isotopic characteristics, igneous activity of Rugoso, Jo Cousin and Pico Pia seamounts is most likely correlated with the sixth post-rifting magmatic stage (32-0 Ma) identified in the eastern NCA margin. Following the convergence Africa-Eurasia, between the Oligocene and the present day, volcanism in this region is confined to the African plate, only having expression in the vicinity of the central and southern branches of the Azores-Gibraltar Fracture Zone.