The Adrar Souttouf Massif (ASM), situated along the western edge of the West African Craton (WAC) in southern Morocco, forms a critical segment of the Souttoufide belt, historically linked to the northern Mauritanides. Thrust onto the Archaean Reguibat Shield, this massif encompasses four NNE-SSW-trending units-Oued Togba, Sebkha Gezmayet, Dayet Lawda, and Sebkha Matallah-hosting a diverse array of igneous, metamorphic, and sedimentary formations. Petrographic study of 22 mafic samples from the Dayet Lawda and Sebkha Matallah units, including metabasalts, metagabbros, olivine gabbros, hornblende gabbros, metadiorites, and gabbro-diorites, reveals preserved igneous structures (ophitic, cumulate, oikocrystic) with mineral assemblages such as plagioclase (An(45-93.9)), olivine (Fo(72.8-83.5)), clinopyroxene (diopside-augite), amphibole (pargasite-edenite), and FeTi oxides, variably overprinted by high-temperature ultrahigh-pressure (HT-UHT) to amphibolite-facies metamorphism (approximate to 975 degrees C, approximate to 1.2 GPa at similar to 604 Ma). Whole-rock geochemistry indicates subalkaline tholeiitic to transitional compositions (SiO2 45-57 wt%, MgO 1.5-11.5 wt%), characterized by enrichment in large-ion lithophile elements (Ba, Rb, Sr), depletion in high-field-strength and heavy rare earth elements (Nb, Ta, Yb), and positive Eu anomalies (Eu/Eu* = 1.2-1.8). Low K/P ratios (2.28-15.22, mostly <7) and high Ti/Yb (1866-5595) suggest limited crustal influence, while Ce/Yb (<20) and La/Ta (<22) are consistent with melting of an asthenospheric spinel peridotite source. SmNd isotopic data (epsilon Nd-6(0)4 Ma = +2.6 to +9.9) and UPb zircon ages (similar to 611-606 Ma) link the ASM to Neoproterozoic magmatism along the southern margin of the WAC, broadly coeval with the Central Iapetus Magmatic Province. Trace-element discrimination diagrams (e.g., Ti/V; Th/Yb vs. Nb/Yb) show a progression from intraplate-like signatures in high-MgO rocks to arc- or back-arc-like traits in more evolved compositions. Taken together, these features are best interpreted as reflecting a polyphase tectono-magmatic evolution compatible with a rift-to-arc transition, in which early extensional magmatism was progressively overprinted by subduction-related influences during Pan-African II convergence, prior to incorporation into the West Gondwana Orogen and subsequent Variscan reworking (similar to 330-300 Ma).

Several synthetic papers have been published about the geological structure of the threeWest African fold belts (Rokelides, Bassarides and Mauritanides), which were attached to the western margin of the West African Craton. Owing to the paucity of radiometric ages, some orogens and tectonic events have previously been confused and little consensus exists regarding their geodynamic evolution. Matching previous geological geochronological and geophysic data with nine new radiometric U-Pb ages on zircon, allows us to propose a new geodynamic model. Apart from ages of Mesoproterozoic events, four different orogens have been distinguished: Pan-African I (ca. 900 to 640 Ma), Pan-African II (ca. 640 to 520 Ma), Mali-Rokel River (ca. 490 to 450 Ma) and Variscan (ca. 450 to 300 Ma). The pan-African I orogeny is characterized by a complex evolution, terminating with a subduction process to the West, including the formation of a volcanic arc and a collisional event between ca. 660 and 640 Ma. The pan-African II orogen corresponds to a subduction process to the East leading to the building of a new volcanic arc and the formation of a back-arc basin to the East. Thenewly evidencedMali-Rokel River orogenic event led to the formation of extensive intra-continental N-S directed basins. The latter were folded and thrusted before the deposition of early Palaeozoic molasses. In the course of the Variscan Orogeny the Palaeozoicbasins setting in Mauritania and Northern Senegal were deformed during the Carboniferous Pangaea assembly. These two later orogensare intra-continental in the area but likely linked to far-field oceanic subduction to the West.For each orogenic period in the belts there are contemporaneous sedimentary deposits on the West African Craton and, of course, related unconformities between them. These data have facilitated correlations between the West African Belts and with the belts setting in adjacent areas like the Appalachians to the West and the northern Brazilian belts to the South.

In the course of the Carboniferous to Permian assembly of Pangaea, large parts of eastern Laurussia and northern Gondwana were affected by the Variscan Orogeny. Here, we particularly focus on the Appalachian belt of eastern Laurentia and the Mauritanide of western Gondwana. Owing to the irregular shapes of the craton margins, the collision between the Laurentia and the West African Craton provides several conjugate promontories and embayments alongside both cratons. Among others, the coupled pair formed by the African Reguibat promontory and its counterpart in North America, the Pennsylvania embayment is the principal subject of this study. The western movement of the Reguibat Shield had initially imprinted the West African belts but finally also affected the Appalachians. Forming such a “punch mark” producing two specific lobes (stacks of nappes) on both sides of the promontory. The southern NW-SW lobe (e.g. Akjoujt nappes) is known since a long time. However, the northern lobe of the “Adrar Souttouf Massif” has not been identified previously owing to its partially covering and also by its N-S alignment instead of an expected symmetrical SW-NE direction. Furthermore, the Adrar Souttouf Massif is partially covered by allochthons terranes (WTB or Appalachians). This new discovery supports a classical impingement model for the deformation of the North American and African belts by westward moving of the Reguibat Shield.

The Miocene calc-alkaline igneous activity in Northern Algeria is restricted to a narrow (50 km) coastal zone along the Mediterranean Sea. It occurs either in the external or in the internal units of the Alpine Tellian belt. The latter resulted from three episodes of nappe thrusting between Lower Burdigalian and Middle Tortonian. Comparatively, K-Ar ages of igneous rocks span between 17 and 9 Ma. The intensity of the various tectonic phases varies by sector through the Tellian belt. Between the three periods of thrusting, a significant detrital sedimentation took place and was accompanied by emplacement of calc-alkaline igneous materials as plutonic and/or volcanic bodies. The main objective of this study is to outline the relationships between Miocene igneous eruptions and their associated sedimentary formations that make up a key portion of the Algerian Alpine belt. For this purpose, we gathered geochronological, geochemical and isotopic data from Miocene cal-alkaline igneous rocks emplaced over more than 800 km near the Algerian coast. In some sectors, the emplacement of igneous rocks within the sedimentary series allows a direct observation of their relationships. K-Ar ages carried on calc-alkaline igneous rocks collected between Tenes-Cherchel and Cap de Fer sectors range from 17.0 Ma to 9.10 Ma. Stratigraphic columns exhibit three successive tectonic cycles at 17 Ma, 15 Ma, and 9 Ma, which correspond to the three southward thrusting events (Burdigalian, Langhian and Tortonian) of Kabylian terranes responsible for the Alpine nappe stack. In various locations, these nappes include igneous rocks as volcanic levels or plutonic bodies. These new results, together with a critical review of previous studies, allow us to discuss the consistency between paleogeography, tectono-magmatic pulses and petro-geochemical evolution of northern Algeria after the closure of the Alpine Tethys.

During the course of the Carboniferous to Permian, large parts of eastern Laurentia and northern Gondwana were affected by the Variscan Orogeny accompanying the assembly of Pangea. Here, we concentrate on the Appalachian belt of eastern Laurentia and the Mauritanide of western Gondwana. Owing to the irregular shapes of the craton margins, the collision between Laurentia and the West African Craton provides several conjugate promontories and embayments alongside both cratons. Among others, the coupled pair formed by the African Reguibat promontory and its counterpart in North America, the Pennsylvania embayment, is the principal subject of this study. The western movement of the Reguibat Shield had initially imprinted the West African belts but finally also affected the Appalachians. Acting as a “hallmark”, it produced two specific lobes (stacks of nappes) on both sides of the promontory. The southern NW-SW lobe (Akjoujt nappes) is long known. However, the northern lobe of the “Adrar Souttouf Massif” has not been identified previously, owing to being partially covered and also to its N-S alignment instead of an expected symmetrical SW-NE direction. Furthermore, the Adrar Souttouf Massif is partially covered by allochthonous terranes (Western Thrust Belt, TB, or Appalachians). This new discovery supports a classical impingement model for the deformation of the North American and African belts by westward displacement of the Reguibat Shield.

Precambrian metasediments provide a unique archive for understanding Earth’s earliest biosphere, however traces of microbial life preserved in ancient rocks are often controversial. In this study we leveraged several micro- to nano-scale techniques to study filamentous structures previously reported in clastic sediments of the 3.22 Ga Moodies Group, Barberton Greenstone Belt, S. Africa. We performed petrographic, mineralogical, electron microprobe, confocal fluorescence and electron microscopy analyses of these structures in order to evaluate their biogenicity and syngenecity. We also examined drill core samples of deep-water iron formations from the 2.46 Ga Joffre member of the Brockman Iron Formation (Hamersley Basin, W. Australia) to better understand their potential biogenicity. In both cases, we aimed to resolve primary vs. secondary mineral assemblages and their relation to filamentous or sedimentary structures. In the Moodies Group samples, filamentous structures were resolved by confocal imaging and revealed to be crosscut by later metamorphic phases, highlighting their syngenetic nature. Three-dimensional imaging reveals that while the filamentous structures are not necessarily associated with grain boundaries (e.g., as organic coatings), they form both sheets and filaments, complicating their interpretation but not ruling out a biological origin. No organic microstructures appeared to be preserved in our Dales Gorge samples. We also examined the possible application of electron paramagnetic resonance spectroscopy (EPR) to carbonaceous matter in ancient silica-rich matrices, similar to [Bourbin et al. (2013)][1], using samples from the Brockman iron formation. While resonance associated with organic matter was largely unresolvable in the Brockman iron formation samples due to their low organic matter contents, large effects on the EPR spectra were apparent stemming from the presence of magnetic iron minerals, highlighting the need to carefully consider sample composition in EPR analyses targeting ancient organic matter. Collectively, this study highlights the added value of micro- to nano-scale techniques as applied to Precambrian metasediments containing traces of ancient life, for example in revealing the pre-metamorphic emplacement and three-dimensional structure of filaments in the Moodies Group, but also the potential drawbacks and pitfalls, such as the case of strong magnetic mineral interference in EPR analysis of organic matter in trace abundance in the Dales Gorge.### Competing Interest StatementThe authors have declared no competing interest. [1]: #ref-2

Late to post-orogenic lamprophyres of the European Variscides attest variable compositions of the mantle beneath the structural zones of the belt. These compositions resulted from different contributions of mantle components involving geotectonic processes during the orogeny, such as oceanic subduction of mafic crust and sediments, continental subduction, collision with mantle input, and delamination of overriding plates. For documenting these processes, we have surveyed three sites of lamprophyre intrusions in the Vendean part of the South Armorican tectonic Zone with spessartite sills and minette dykes, and a fourth site in the West-Armorican kersantite swarm. The age of spessartite is estimated between 320 and 315 Ma on the base of structural relationships with the dated neighbouring granite. Dykes of minette share similar intrusive setting along the post-orogenic NW–SE dextral shear zones. One dyke is dated at 286.2 ± 6.6 Ma (Early Permian) by K/Ar method. The Western Brittany kersantite swarm is Middle to Late Carboniferous in age. All these rocks display common mineral and chemical compositions of lamprophyres. A review of the Variscan European lamprophyres is conducted in order to document their geochemical fingerprints compared with those of the studied samples.

The Bafoussam area in western Cameroon is part of the central Cameroon Volcanic Ligne (CVL). This study presents the mineralogy, major and trace element compositions, Sr-Pb-Hf isotopes, and new K–Ar geochronological data about mafic and felsic volcanic rocks. These rocks belong to two different series: A transitional series made of basalts, basaltic andesite, and trachytes and an alkaline mafic series with basalts, hawaiites, and basanites. New age data show that the transitional series belongs to the oldest part of the CVL and was emplaced between 47 and 35 Ma. The alkaline volcanism is younger, with ages ranging from 10 to 4.5 Ma. Magmatic evolution in both series is accomplished through a fractional crystallization process, with the removal of olivine and clinopyroxene, while plagioclase does not seem to be a major crystallizing phase. All the samples are enriched in incompatible trace elements, but the rocks from the alkaline series have more fractionated REE patterns and high Nb content compared to the transitional mafic lavas. Alkaline lavas have lower initial 87Sr/86Sr and higher 176Hf/177Hf and Pb isotopic ratios than the transitional lavas. Low La/Nb and high 87Sr/86Sri ratio are among chemical characteristics that show that some samples from the transitional series have interacted with a crustal component during their evolution in the crust. They cannot be used for discussing the mantle source of the volcanic rocks from this series. Trace elements show that primary magmas for both series formed in a garnet-bearing mantle source, with higher partial melting degrees (3–5

The Cretaceous Ngaou Boh anorogenic complex (NBAC) located in the far North Adamawa Plateau, the centre domain of the Cameroon Line constitutes a plutonic-volcanic ring association. The whole rock K-Ar datation yields a crystallization age of ca. 74 Ma. Plutonic rocks comprise abundant alkali feldspar granites, scarce clinopyroxene-amphibole gabbros and alkali feldspar syenites. Alkali feldspar granites are leucocratic, coarse to fine-grained; quartz and K-feldspars are the major rock-forming mineral, besides minor oligoclase, biotite and accessory phases as sphene, zircon and opaques. Alkali feldspar syenites are mesocratic coarse-grained, mainly composed of K-feldspars with small amounts of quartz and biotite. Volcanic rocks consist of a basanite-trachyte-rhyolite suite. Basanites contain olivine and diopside phenocrysts and a groundmass essentially composed of plagioclase and titanomagnetite. Biotite-clinopyroxene trachytes and clinopyroxene-amphibole rhyolites have an almost homogeneous modal composition, mainly made up of sanidine and anorthoclase microliths, scarce phenocrysts of quartz, and minor crystals of biotite, clinopyroxene (augite) amphibole (pargasite, sandagaite); Fe-Ti oxides (ilmenite, titanomagnetite) and fibreglass are often isolated in the groundmass. Plutonic rocks are alkaline, weakly metaluminous with some alkali feldspar granites displaying agpaitic or peralkaline feature. Incompatible Trace elements (HFSE and LILE) distribution and chondrite-normalized REE patterns evidence a significant petrogenetic link between clinopyroxene-amphibole gabbros, alkali feldspar syenites and alkali feldspar granites. All the analysed samples are enriched in incompatible elements, indicating melts from spinel and garnet-bearing mantle source close to OIB component. Indeed, the (Tb/Yb)N ratios of both basanites (2.3-2.5) and clinopyroxene-amphibole gabbros (1.4-1.9) suggest different parental magma sources. Alkali feldspar granites appear as residue of magma differentiation led by crystal fractionation of liquid derived from the partial melting of spinel peridotite mantle. Clinopyroxene-amphibole rhyolites and biotite-clinopyroxene trachytes (Mg#=0.0-15.4) derive through fractional crystallization from basanites (Mg#=64.3-60.1), the most primitive mafic parental melt. Both plutonic rocks and lavas trends evidence a bimodality highlighted by a pronounced “Daly gap”.

We present the first K-Ar geochronological and geochemical data (major and trace elements, as well as Sr, Nd, Pb, and Hf isotopes) on volcanic rocks from the Fotouni lavas in the central part of the Cameroon volcanic line (CVL). Two distinct compositional groups can be discriminated: alkaline and transitional lavas. The alkaline series ranges in composition from basanite and basalt to hawaiite and formed 14 to 3 Ma ago while the transitional series ranges from basalt and trachybasalt to basaltic trachyandesite and formed 47 to 38 Ma ago. All samples display trace element patterns dominated by light rare-earth element enrichments compared to heavy rare-earth elements. The alkaline samples have (87Sr/ 86 Sr)i ranging from 0.70292 to 0.70340, ε Nd = 3.45 to 5.98, ɛ Hf = 1.95 to 5.63, and relatively radiogenic Pb isotopic compositions: 206 Pb/ 204 Pb = 19.891–20.592; 207 Pb/ 204 Pb = 15.639–15.693; 208 Pb/ 204 Pb = 39.566–40.044. Transitional basalts are characterized by relatively radiogenic Sr and unradiogenic Nd, Hf, and Pb: (ɛ Nd )i = − 10.82 to + 3.43; ɛ Hf = − 14.00 to + 3.13; 206 Pb/ 204 Pb = 18.0716 to 18.9274; 207 Pb/ 204 Pb = 15.532 to15.704; 208 Pb/ 204 Pb = 37.8141 to 39.4735. Several geochemical characteristics indicate that the transitional lavas have interacted with the continental crust while alkaline lavas did not suffer significant amounts crustal contamination. Both transitional and alkaline lava series can be explained by mixing between two mantle components: an enriched component and a HIMU-like component. These two mantle sources are probably located within the lithospheric mantle and are different from both the Saint Helena and the Mont Cameroon mantle.

We present new geochemical and isotopic data for rock samples from two island arc volcanoes, Erromango and Vulcan Seamount, and from a 500 m thick stratigraphic profile of lava flows exposed on the SW flank of Vate Trough back‐arc rift of the New Hebrides Island Arc (NHIA). The basalts from the SW rift flank of Vate Trough have ages of ~0.5 Ma but are geochemically similar to those erupting along the active back‐arc rift. The weak subduction component in the back‐arc basalts implies formation by decompression melting during early rifting and rifting initiation by tectonic processes rather than by lithosphere weakening by arc magma. Melting beneath Vate Trough is probably caused by chemically heterogeneous and hot mantle that flows in from the North Fiji Basin in the east. The melting zone beneath Vate Trough back‐arc is separate from that of the arc front, but a weak slab component suggests fluid transport from the slab. Immobile incompatible element ratios in South NHIA lavas overlap with those of the Vate Trough depleted back‐arc basalts, suggesting that enriched mantle components are depleted by back‐arc melting during mantle flow. The slab component varies from hydrous melts of subducted sediments in the Central NHIA to fluids from altered basalts in the South NHIA. The volcanism of Erromango shows constant compositions for 5 million years, that is, there is no sign for variable depletion of the mantle or for a change of slab components due to collision of the D'Entrecasteaux Ridge as in lava successions further north.

Miocene K-rich calc-alkaline magmatic rocks are exposed over a ~ 150 km2 area in Cap de Fer and West Edough, along the NE Algerian Mediterranean coast. They include andesitic pyroclastic and lava flows, small dioritic plutons, and large microgranodioritic intrusions that intrude and/or overlie Miocene sediments. New 40K-40Ar ages obtained on the igneous rocks range from 16.84 ± 0.58 to 12.91 ± 0.31 Ma and define three successive magmatic pulses at ~ 16.5, ~ 15, and ~ 13 Ma. These data are in good agreement with biostratigraphic data obtained on the Miocene marls that yielded Langhian (N8 biozone) to Late Langhian-Serravallian ages (N9–N10 biozones). This consistency suggests that the time span (~ 3.5 m.y.) deduced from K-Ar datings is not due to perturbations of the K-Ar clock; it is more likely related to long-lasting tectono-magmatic processes. According to the regional context (“no-slab” area), these processes result from the uprise of hot asthenospheric mantle through the tear generated by the detachment of the oceanic part of the African slab beneath the Algerian margin that triggered the partial melting of the overlying metasomatized lithospheric mantle of the Kabylides.

In the Cameroon Pan-African orogenic belt, the West Cameroon Domain (WCD) is characterized by the apparent lack of Archean-Paleoproterozoic relicts, the development of Neoproterozoic basins and abundant plutonic massifs. The Hossere Mana plutonic complex (HMPC) and the Gapi gabbroic stock are located in the vicinity of the Cretaceous Ngaou Boh granite complex and the Neogene Tchabal Gangbada basanite-trachyte-rhyolite volcanic plateau. They comprise clinopyroxene + amphibole +/- olivine leucogabbro, clinopyroxene + amphibole monzogabbro, biotite + amphibole +/- clinopyroxene monzodiorite, porphyritic and foliated biotite +/- muscovite monzogranite. Two parallel trends of Mg#, displayed by leucogabbro (0.66-0.61) monzogabbro (0.57-0.37), and by monzodiorite (0.66-0.55) -monzogranite (0.47-0.33), evidence two contrasting igneous suites, magnesian tholeiitic and magnesian high-K alkali-calcic to talc-alkaline (I-type). Primitive mantle-normalized patterns of the tholeiitic suite are fractionated, with no significant HFSE anomalies, suggesting a garnet-bearing enriched peridotite source. Primitive mantle-normalized patterns of the high-K alkali-calcic to talc-alkaline suite include more fractionated felsic types and display Nb-Ta negative anomalies, suggesting another source with amphibole - garnet in the residue and possible origin of felsic rocks by partial melting of mafic lower crust with garnet and titanite-rutile in the residue. In leucogabbro, fairly low Sri (0.70538) and little negative eNd(750 Ma) ( + 0.2), with a TDM single-stage Nd model age of 1.42 Ga, are consistent with magmas extracted near the lithosphere - asthenosphere boundary from an enriched mantle source close to BSE (Bulk Silicate Earth). In monzodiorite, little higher Sri (0.70628) and strongly negative eNd (560 Ma) ( - 8.8), with a TDM single-stage Nd model age of 1.64 Ga, point to a supplementary (lithospheric?) mantle source metasomatized by subduction products. HMPC and GS massifs, emplaced in a syn-to post-kinematic environment after the major collision stage, illustrate coeval magnesian tholeiitic and magnesian high-K alkali-calcic talc-alkaline (I-type) igneous suites, in which primary magmas were tapped from different mantle sources, followed by younger felsic suite issued from garnet-bearing lower crustal source.

El Complejo Igneo La Tesorera (CIT) esta compuesto por una secuencia sedimentaria y vulcanosedimentaria mesozoica perteneciente al terreno Guerrero (TG) asi como de sedimentos calcareos del Cretacico Temprano, deformados por el evento de acortamiento de la orogenia Laramide, y finalmente intrusionado por la Granodiorita Tesorera alrededor de 74 Ma. En el Paleogeno tardio se emplazaron domos volcanicos de lavas daciticas sobre la granodiorita, seguidos de un conjunto de diques y domos rioliticos extravasados en el rango de 50 y 44 Ma. La secuencia vulcano sedimentaria cretacica se deposito en un ambiente de intraa tras-arco. El desarrollo del arco volcanico de la Sierra Madre Occidental durante el Cretacico Tardio es contemporaneo a la orogenia Laramide y esta asociado con el cinturon de pliegues y cabalgaduras de la Sierra Madre Oriental, provocando el ensamble final del terreno Guerrero con el terreno Sierra Madre. En la Granodiorita Tesorera, diques y domos felsicos asociados al arco volcanico de la Sierra Madre Occidental, fueron emplazados a lo largo de fallas y fracturas con orientacion NW con anchos variables hasta de 500 m y longitud de ~5 km y sobre las unidades mesozoicas que forman el arco volcanico Asientos-La Tesorera (definido asi en este trabajo). Los intrusivos granodioriticos de esta porcion meridional de la Mesa Central no presentan deformacion contractil laramidica y se emplazaron en la zona donde se intersectan el sistema de fallas San Luis-Tepehuanes (SFSLT) y el hombro oriental del graben de Aguascalientes. Los diques eocenicos presentan rumbo promedio de N60oW, con inclinacion entre 45° y 85° SW, sugiriendo una extension en direccion ~NE-SW para este periodo de tiempo. De acuerdo con la edad de las rocas volcanicas del area de estudio, la deformacion que origino los conductos para el ascenso de las lavas pertenece a las etapas iniciales

Miocene (17-11 Ma) magmatic activity in the Kabylies emplaced K-rich (and minor medium-K) calcalkaline plutonic and volcanic rocks in five zones, delineating a similar to 450 km long EW trending strip located along the northern coast of Algeria, between Annaba and Algiers. Their most likely source is the Kabylian subcontinental lithospheric mantle previously metasomatized during the Paleogene subduction of the Tethys oceanic lithosphere. Our preferred tectono-magmatic model involves a Tethyan slab detachment combined with African mantle delamination and crustal stacking, leading to the superimposition of the African continental crust over the Kabylian metasomatized lithospheric mantle. At ca. 17 Ma, the asthenospheric upwelling arising from lithospheric delamination and Tethyan slab tear triggered the thermal erosion of the latter mantle, inducing its partial melting. The corresponding mafic medium-K talc-alkaline magmas interacted with the African basement units during their ascent, generating intermediate to felsic K-rich talc-alkaline melts that display a characteristic trace element and isotopic crustal signature. Later on, slab tears propagated eastward and westward, promoting slab rollback perpendicular to plate convergence and inducing the emplacement of magmatic rocks of decreasing ages from central eastern Algeria towards Tunisia and Morocco. (C) 2016 Elsevier Ltd. All rights reserved.

Intraplate deformation is most often linked to major stress applied on plate margins. When such intraplate events are accompanied by magmatism, the use of several dating methods integrated within a multidisciplinary approach can bring constraints on the age, nature and source mobilized for generating the magma and in turn on the nature of the intraplate deformation. This study focuses on the large gabbro Arrikine sill (35 km in extension) emplaced within the Silurian sediments of the western margin of the Murzuq cratonic basin in southeastern Algeria. Its emplacement is dated during the early Devonian (415-400 Ma) through the determination of a reliable paleomagnetic pole by comparison with the Gondwana Apparent Polar Wander Path (APWP). This age can be correlated with deep phreatic eruptions before Pragian time thought to be at the origin of sand injections and associated circular structures in Algeria and Libya. For the sill, the K -Ar age of 325.6 +/- 7.7 Ma is related to a K-rich aplitic phase that has K-enriched by more than 20% the Devonian gabbro. Laser-ICP-MS U-Pb method dates only inherited zircons mostly at c. 2030 Ma with additional ages at c. 2700 Ma and younger ones in the 766-598 Ma age range. The Arrikine sill is a high-Ti alkaline gabbro having the geochemical composition of a hawaiite akin to several intraplate continental and oceanic provinces, including the contemporaneous Air ring complexes province in Niger, but also to the Mauna Loa volcano in Hawaii. This peculiar composition akin to that of the contemporaneous Air province is in agreement with a lower Devonian age for the Arrikine sill.The lower Devonian Arrikine sill emplacement is related to a "Caledonian" transtensive reactivation of the western metacratonic boundary of the Murzuq craton. This event also generated in the Saharan platform the so-called "Caledonian unconformity" of regional extension, the Air ring complexes and magmatic rocks that produced sand injections. It could be related to rifting of the Hun terranes that occurred at the plate margin to the north (Stampfli and Borel, 2002, Blackey, 2008 and references therein). The mid-Carboniferous (c. 326 Ma) reactivation corresponds to Variscan compression on NW Africa generating aplitic fluids, but also"to the major "Hercynian unconformity" of regional extension. Thegeneration of the Arrikine magma is attributed to partial melting through adiabatic pressure release of uprising asthenosphere along tectonically reactivated mega-shear zones, here bordering the relictual Murzuq craton enclosed in the Saharan metacraton. (C) 2015 Elsevier Ltd. All rights reserved.

At the southern tip of the Baja California peninsula, we characterize the onshore structures and kinematics associated with crustal necking leading up to the Pliocene breakup and early East Pacific Rise seafloor spreading. From a combination of tectonic field investigations, K-Ar and cosmogenic isotope dating and geomorphology, we propose that the Los Cabos block represents the exhumed footwall of a major detachment fault. This north trending detachment fault is marked by a conspicuous low-dipping brittle-ductile shear zone showing a finite displacement with top to the SE ending to the ESE. This major feature is associated with fluid circulations which led to rejuvenation of the deformed Cretaceous magmatic rocks at a maximum of 17.5Ma. The detachment footwall displays kilometer-scale corrugations controlling the present-day drainage pattern. This major detachment is synchronous with the development of the San Jose del Cabo Basin where syntectonic sedimentation took place from the middle Miocene to probably the early Pliocene. We propose that this seaward dipping detachment fault accommodates the proximal crustal necking of the Baja California passive margin, which predates the onset of formation of the East Pacific Rise spreading axis in the Cabo-Puerto Vallarta segment. Our data illustrate an apparent anticlockwise rotation of the stretching direction in Baja California Sur from similar to 17 Ma to the Pliocene.

The Kivu rift is part of the western branch of the East African Rift system. From Lake Tanganyika to Lake Albert, the Kivu rift is set in a succession of Precambrian zones of weakness trending NW-SE, NNE-SSW and NE-SW. At the NW to NNE turn of the rift direction in the Lake Kivu area, the inherited faults are crosscut by newly born N-S fractures which developed during the late Cenozoic rifting and controlled the volcanic activity. From Lake Kivu to Lake Edward, the N-S faults show a right-lateral en echelon pattern. Development of tension gashes in the Virunga area indicates a clockwise rotation of the constraint linked to dextral oblique motion of crustal blocks. The extensional direction was W-E in the Mio-Pliocene and ENE-WSW in the Pleistocene to present time.The volcanic rocks are assigned to three groups: (1) tholeiites and sodic alkali basalts in the South Kivu, (2) sodic basalts and nephelinites in the northern Lake Kivu and western Virunga, and (3) potassic basanites and potassic nephelinites in the Virunga area. South-Kivu magmas were generated by melting of spinel + garnet lherzolite from two sources: an enriched lithospheric source and a less enriched mixed lithospheric and asthenospheric source. The latter source was implied in the genesis of the tholeiitic lavas at the beginning of the South-Kivu tectono-volcanic activity, in relationships with asthenosphere upwelling. The ensuing outpouring of alkaline basaltic lavas from the lithospheric source attests for the abortion of the asthenospheric contribution and a change of the rifting process. The sodic nephelinites of the northern Lake Kivu originated from low partial melting of garnet peridotite of the sub-continental mantle due to pressure release during swell initiation. The Virunga potassic magmas resulted from the melting of garnet peridotite with an increasing degree of melting from nephelinite to basanite. They originated from a lithospheric source enriched in both K and Rb, suggesting the presence of phlogopite and the local existence of a metasomatized mantle. A carbonatite contribution is evidenced in the Nyiragongo lavas.New K-Ar ages date around 21 Ma the earliest volcanic activity made of nephelinites. A sodic alkaline volcanism took place between 13 and 9 Ma at the western side of the Virunga during the doming stage of the rift and before the formation of the rift valley. In the South-Kivu area, the first lavas were tholeiitic and dated at 11 Ma. The rift valley subsidence began around 8-7 Ma. The tholeiitic lavas were progressively replaced by alkali basaltic lavas until to 2.6 Ma. Renewal of the basaltic volcanism happened at ca. 1.7 Ma on a western step of the rift. In the Virunga area, the potassic volcanism appeared ca. 2.6 Ma along a NE-SW fault zone and then migrated both to the east and west, in jumping to oblique tension gashes.The uncommon magmatic evolution and the high diversity of volcanic rocks of the Kivu rift are explained by varying transtensional constraints during the rift history. (C) 2016 Elsevier Ltd. All rights reserved.

The age and origin of the volcanism along the Cameroon Volcanic Line (CVL) are still a matter of debate. We present major and trace element compositions as well as Sr–Nd–Pb–Hf isotopic results for mafic rocks from the Bamoun area, in the central part of the Cameroon Volcanic Line, as well as for two samples from recent eruptions of Mt. Cameroon. Lava flows are mostly basalts and hawaiites with transitional affinity. Some samples are among the oldest rocks of the CVL, with ages older than 51 My while some rocks are very young, around 0.05 My. All the samples are enriched in incompatible elements, indicating that melts were formed in a garnet-bearing mantle source. Different mantle sources participated to the formation of the Bamoun lavas. One source is isotopically similar to the main volcanic rocks of the CVL and probably represents an important part of the subcontinental lithospheric mantle. The second source is enriched in incompatible elements and shows a marked positive Eu anomaly, probably related to the participation of pyroxenites in the partial melting processes. The third mantle source is similar to the source of the Mt. Cameroon. This mantle source was known previously only in the Mt. Cameroon lavas, and we report its occurrence for the first time in old lavas and in other location along the CVL.