Magmatism plays a central role in rift dynamics, yet the structure and evolution of magma plumbing systems during continental break-up remain poorly constrained. The Afar Rift offers a rare opportunity to study active plate divergence and associated magma processes. We investigate the 1978 Ardoukoba fissural eruption in the Asal Rift, a syn-rift volcanism archetypal example and the most recent eruption in this segment of the Afar Rift system. Using a comprehensive dataset of melt inclusion and host mineral compositions, volatile contents (H2O, CO2, delta D), and thermobarometry, we reconstruct the transcrustal plumbing system and track magma storage, transfer, and degassing during the eruption. Our results reveal polybaric magma recharge events destabilizing the system, triggering progressive tapping of increasingly deeper mush zones. The eruption began with shallow, evolved melts and transitioned to deeper, more primitive melts and crystal cargos. These findings offer a high-resolution view of magma dynamics during rifting and provide key constraints on the magmatic architecture of incipient oceanic spreading centers.

The architecture of plumbing systems, and the dynamics of magma-mush mobilisation during eruptions have received a great deal of attention in recent years. Magmatism plays a central role in rift dynamics, yet the structure and evolution of magma plumbing systems during continental break-up remain poorly constrained. The Afar Rift offers a rare opportunity to study active plate divergence and associated magma processes. We investigate the 1978 Ardoukoba fissural eruption in the Asal Rift, a syn-rift volcanism archetypal example and the most recent eruption in this segment of the Afar Rift system. Using a comprehensive dataset of melt inclusions and host mineral compositions, volatile contents (H₂O, CO₂, δD) and thermobarometry, we reconstruct the transcrustal plumbing system and track magma storage, transfer and degassing during the eruption. We show that magmas feeding the system derived from heterogeneous mantle sources, whose signatures are preserved in melt inclusions. Our results reveal polybaric magma recharge events destabilizing the system, triggering progressive tapping of increasingly deeper mush zones. The eruption began with shallow, evolved melts and transitioned to deeper, more primitive melts and crystal cargos. These findings offer a high-resolution view of magma dynamics during rift-related eruptions and provide key constraints on the magmatic architecture of incipient oceanic spreading centres.

The Asal Rift, situated within the Afar region, presents a unique opportunity to study continental rifting and ongoing break-up mechanisms. Here we present a comprehensive study based on volatile element contents of magmas within the Asal rift's segment. Samples were gathered from various volcanic sub-segments within the active part of the Asal rift, and a subset was collected to document the successive steps of the recent 1978 Ardoukoba eruption. Altogether our new sampling is offering a chronological framework crucial to understanding this magmatic system and the eruptive sequences. Quenched pyroclastic deposits (scoria) were used as they are more likely to preserve the magma's volatile content without significant degassing upon cooling at surface than lava flows. By analyzing over 400 melt inclusions within plagioclase and olivine crystals of 15 new samples, we provide insight into the pre-eruptive volatile content of Asal magmas. The melt inclusions volatile contents (H2O, CO2, Cl, and S) were quantified through SIMS analyses at CRPG. Sample preparation for SIMS measurements was carefully achieved to avoid any contamination or volatile loss. After estimation of the volatile migration through the shrinkage bubbles of the melt inclusions by Raman spectroscopy, and correction from post-entrapment crystallization processes, we reconstructed the initial magmatic volatile content at the reservoir depth. This content, combined with detailed petrographic study, field observations, and new dating, allows us to propose a comprehensive picture of the Asal Rift plumbing system architecture, and to discuss its spatial variability and temporal evolution. The wealth of data allowed us to highlight a relative homogeneity of the reservoir volatile contents over the recent Asal rift segment erupted magmas, and to discern the depth range of the Asal igneous reservoir that spans from approximately 5 km to 25 km (based on solubility models of VESIcal (1)). Furthermore, volatile data, combined with in-situ major and trace element analysis, provides insights into magma differentiation, degassing, and into the volatile content of the mantle source. We investigate 3 potential steps of degassing and their effect on volatile, trace and major element: within the plumbing system (during the differentiation), during magma ascent, and at the surface during the eruption (unlikely given the sampling method). Finally, our study focused on the 1978 Ardoukoba eruption within the Asal rift. With a sampling of the entire eruptive sequence, we were able to highlight the evolution of the volatile content during this eruption, showing that the initial differentiated magma reservoir underwent a recharge event before eruption. In conclusion, this new in-situ high-resolution volatile, trace and major element extended dataset 1/ delineated the extensive depth range of the magmatic reservoir, 2/ allows a better understanding of the dynamics of magma reservoirs that feed continental rift systems, and 3/ provides new constraints on the magma evolution, differentiation, and degassing at depth within such a system. (1) Iacovino, K., Matthews, S., Wieser, P. E., Moore, G. M., & Bégué, F. (2021). VESIcal Part I: An Open‐Source Thermodynamic Model Engine for Mixed Volatile (H2O‐CO2) Solubility in Silicate Melts. Earth and Space Science, 8(11).

The Afar region provides a rare onshore glimpse into the dynamic processes of magmatic continental rifting and the progression towards continental break-up. This area features multiple active magmatic segments distinguished by varied morphologies, crustal thicknesses, rates of magma production, and magmatic-tectonic styles. In the Erta Ale Range rift segment, extension is accommodated magmatically, making it an ideal location to study the magmatic behavior of a mature rift segment. The Erta Ale Range includes sub-segments with magma compositions ranging from basalts to rhyolites, but only the Erta Ale Volcano (EAV) sub-segment is currently active, where only basaltic compositions have been reported so far. Our analyses of major and trace elements, along with isotopic studies of olivine crystals, interstitial glasses, and melt inclusions, combined with oxy-thermo-barometry and thermodynamic modeling, delineate the evolution of magma beneath EAV. We reveal extensive in-situ fractional crystallization within a shallow magmatic reservoir, evidenced by unique cognate gabbroic and microgabbroic blocks. These cognate samples uncover previously unknown mushy and evolved parts (up to 75 wt.% SiO2) of the EAV plumbing system. These findings highlight a sophisticated, transcrustal magmatic plumbing system that contrasts with typical oceanic rift systems, indicating a transitional phase in rift evolution. Our results suggest a magmatic plumbing system that extends up to 12 km in depth, accommodating the rift's extensional dynamics through both magmatic differentiation and tectonic processes. This system is indicative of a rift in an advanced stage of development yet not fully matured to oceanic spreading. Our findings contribute to refining the conceptual models of rift evolution by providing detailed insights into the magmatic and tectonic processes at a critical junction of the Afar rift system. The study emphasizes the complex nature of magmatic systems during the transitional phases of break-up and highlights the need for reconsidering the criteria used to determine the stages of continental break-up. We discuss this model within the geological contexts of the Erta Ale Range rift segment and the larger Afar region, and highlight contrasts with mature oceanic systems to argue that the region is not in the final stages of continental break-up. Pin, Chazot, France, Abily, Gurenko, Bertrand, Loppin, 2024. Protracted magma evolution and transcrustal magmatic plumbing system architecture at Erta Ale volcano (Afar, Ethiopia). Journal of Petrology 65, egae118. https://doi.org/10.1093/petrology/egae118

Copper and gold-rich seafloor massive sulfide deposits formed in intra-oceanic subduction settings are typically associated with hydrous and oxidized magmas, but processes leading to their formation remain controversial. Sulfide-bubble interaction has been suggested to play an important role in metal transfer from magmas to seawater-derived hydrothermal fluids. Here we use textural observations of magmatic sulfides, geochemical numerical models of chalcophile element concentrations, and numerical models of magmatic sulfide growth within a mafic to felsic submarine magmatic suite (Fatu Kapa, SW Pacific) associated with copper-gold-rich seafloor massive sulfide deposits. We demonstrate that concomitant sulfide and aqueous fluid formation at the andesitic stage results in floating sulfide-bubble compound drops in magmas, which play a crucial role in the transfer of copper and gold toward the surface. We emphasize that late sulfide saturation in copper-gold-rich intra-oceanic subduction-derived felsic magmas favors upward sulfide transfer via flotation. The flotation of sulfide-bubble compounds in magmas plays an important role in forming Cu-Au hydrothermal seafloor ore deposits, according to petrographic observations, geochemical and physical modeling.

The Afar region is one of the only places on Earth where magmatic continental rifting and associated ongoing break-up processes are exposed onshore. The several active magmatic segments there are characterized by contrasted morphologies, crustal thicknesses, magma production rates, and magma-tectonic styles. In the Erta Ale Range rift segment, extension is magmatically accommodated, making the range the ideal place to study the magmatic behavior of a mature rift segment. Erta Ale Range comprises sub-segments with magma compositions ranging from basalts to rhyolites, but only the Erta Ale Volcano (EAV) sub-segment is active, where only basaltic compositions have been reported so far. Here, we show for the first time protracted differentiation at EAV that is not expressed volcanically at the surface, but is rather accessible via unique cognate gabbroic and microgabbroic blocks, and recorded by mixing with erupted basaltic magmas. These cognate samples record previously unknown mushy and evolved parts of the EAV plumbing system. To constrain their origin and evolution, we measured the major and trace element compositions of the bulk rocks, interstitial glasses, and melt inclusions. We also measured the oxygen isotopic compositions of olivine crystals, interstitial glasses, and melt inclusions. By combining these results with textural relationships and oxy-thermo-barometry calculations, we discuss magma differentiation and storage conditions, as well as magmatic interactions during transport through the crust. Comparison of our results with rhyolite-MELTS thermodynamic models highlights that protracted fractional crystallization is the main process of magma evolution, and when associated with reactive porous flow is capable of forming the evolved compositions observed (up to 75 wt.% SiO2). We also use the model outputs to quantify distinct steps of igneous differentiation in both shallow and deep crustal reservoirs, and we highlight significant interactions with hydrothermally altered wall rocks. We discuss this model within the geological contexts of the Erta Ale Range rift segment and the larger Afar region, and highlight contrasts with mature oceanic systems to argue that the region is not in the final stages of continental break-up.

The alkaline volcanism of the Cameroon Volcanic Line in its northern domain has raised many fresh enclaves of peridotites. The samples selected come from five (05) different localities (Liri, in the plateau of Kapsiki, Mazélé in the NE of Ngaoundéré, Tello and Ganguiré in the SE of Ngaoundéré and Likok, locality located in the west of Ngaoundé). The peridotite enclaves of the above localities show restricted mineralogical variation. Most are four-phase spinel-lherzolites, indicating that this is the main lithology that forms the lithospheric mantle below the shallow zone. No traces of garnet or primary plagioclase were detected, which strongly limits the depth range from which the rock fragments were sampled. The textures and the wide equilibrium temperatures (884˚C - 1115˚C) indicate also entrainment of lherzolite xenoliths from shallow depths within the lithosphere and the presence of mantle diapirism. The exchange reactions and equilibrium state established in this work make it possible to characterize the chemical composition of the upper mantle of each region and test the equilibrium state of the phases between them. Variations of major oxides and incompatible elemental concentrations in clinopyroxene indicate a primary control by partial melting. The absence of typical "metasomatic" minerals, low equilibration temperatures and enriched LREE patterns indicate that the upper mantle below septentrional crust of Cameroun underwent an event of cryptic metasomatic enrichment prior to partial melting. The distinctive chemical features, LREE enrichment, strong U, Ce and Pr, depletion relative to Ba, Nb, La, Pb, and T, fractionation of Zr and Hf and therefore ligh high Zr/Hf ratio, low La/Yb, Nb/La and Ti/Eu are all results of interaction of refractory peridotite residues with carbonatite melts.

The annular Richat Structure, in Mauritania, is among the most striking geological features on Earth visible from space. Nicknamed "the Eye of Africa", its intriguing concentric shaping has drawn attention for several decades. Formerly hypothesized as an astrobleme, it is now consensually recognized as a complex igneous intrusion, involving two ring-like gabbroic bodies, a central breccia and carbonatite dykes. However, the coexistence of until now undated tholeiitic gabbros and 99 Ma carbonatites akin to alkaline magmatism remained enigmatic. We provide the first plagioclase Ar-40/Ar-39 age determination and new geochemical data on the gabbroic bodies. Although no robust age was obtained, numerical modelling of our results suggests that the gabbros were intruded between 230 and 200 Ma. This age bracket is compatible with the similar to 200 Ma Central Atlantic Magmatic Province (CAMP). Moreover, the compositions of these tholeiitic gabbros match the two chemical groups of the CAMP the best represented in northwest Africa. Therefore, we argue that the Richat gabbros correspond to two CAMP sills intruded conformably into the Late Proterozoic/Lower Paleozoic sedimentary sequences of the Taoudenni basin. About 100 My later, the gabbros and their country rocks were locally uplifted by an alkaline intrusion (expressed now on surface by the carbonatites), resulting in a circular doming, 40 km in diameter. The subsequent erosion led to the actual flattened concentric structure. Therefore, the Richat Structure represents a two-stage igneous-history, separated by a time lapse of similar to 100 My, resulting in two CAMP gabbroic sills mimicking ring-like bodies.

Active volcanic craters are highly dynamic geological features that undergo morphological changes on a broad range of spatial and temporal scales. Such changes have implications for the stability of the edifice, the eruptive style and the associated hazards. However, monitoring the morphological evolution of active craters at high spatial resolution and over long periods of time can be challenging, especially at remote volcanoes. In this study, we demonstrate the potential of Structure-from-Motion Multi-View Stereo photogrammetry technique based on crowd-sourced data, applied to the case study of Oldoinyo Lengai (OL) volcano in northern Tanzania. Following the 2007-08 paroxysm, OL volcano resumed its characteristic effusive activity and started to fill in with lava the newly-formed 300 m wide and 130 m deep pit crater. Monitoring capability is limited at OL due to its location in a remote non-urbanized area, therefore, the eruptive and morphological evolution is poorly constrained (e.g., lava emission rates, number of vents, location of unstable areas), with hazard implications for tourists visiting the summit area. Here we use crowd-sourced images, including Unoccupied Aircraft System (UAS) images, ground-based videos and pictures collected between October 2014 and June 2022, to reconstruct high-resolution topographic time-series of OL's summit crater. With these data, we have generated 7 Digital Elevation Models (DEMs) of OL's pit crater spanning the past 8 years, and estimated the emitted volume of lava and the corresponding time averaged discharge rates (TADR). From this we characterize the geomorphological evolution of OL pit crater since the 2007-08 paroxysm and perform a preliminary hazard assessment of the crater area. InSAR COSMO-SkyMed and Sentinel-1 data covering the periods 2013-2014 and 2018-2019 were also used in this study to complement our observations. Our results indicate that the main location of lava emission within the crater floor has repeatedly shifted over the years and that the 2008 cone has experienced a subsidence over time. OL's TADR has increased over the years, reaching values one order of magnitude higher in the period 2021-2022 compared to 2014-2018. Assuming similar TADR in the coming years, the crater could be filled in by lava within the next decade, leading to new lava overflows on the flanks of the volcano.

Peridotite xenoliths, raised to the surface by alkaline basalts or kimberlites,provide us direct information on the processes and composition of the upper mantle. They are the major source of information on the state of stress,pressure and temperature in the deep mantle. They are thus a source of petrological and geochemical information that is generally not available on the Earth’s surface. Fresh spinel-lherzolite xenoliths exhibit a protogranular components of the Tello volcano. The Tello is the continental sector of the Cameroon Line, located in the South East of the town of Ngaoundéré at 75 km approximately between (N7° 13’, N7° 14’) and (E13° 40’ and E13° 60’). Minerals’ composition of the xenoliths is ~64% olivine, ~24% orthopyroxene, ~11% clinopyroxene and ~1% spinel. Significant variation in (Cr/Cr + Al) of the system shows the reciprocal nature of the spinel solution.The Tello spinel lherzolites show internal chemical homogeneity and represent a normal upper mantle. Their mineral chemistries suggest equilibrium condition of 830° - 925° and 1.4 GPa-2.3 GPa. These data suggest that there is good correlation bracket between increasing activity of Al2O3 and decreasing of practionning of TiO2 into spinel. The AlIV and AlVI contents vary by 0.05-0.2 and 0.03-0.2 respectively. The majority of samples caracterise the lithospheric mantle.

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

There are many volcanic districts in the Adamawa Volcanic Massif in the eastern branch of the Cameroon Volcanic Line. The origin of the volcanism and its mantle sources are still highly debated. Basaltic lavas from the Wakwa plain, one of these districts, provide information on processes that took place beneath this area of anomalous lithospheric and crustal thinning. Major and trace element compositions as well as mineral chemistry are presented in this study. The lavas are basanites, basalts, hawaiites, and foïdites, with porphyritic to glomero-porphyritic and sub-aphyric textures. The minerals are mainly olivine (chrysolite), clinopyroxenes (diopside and augite), plagioclases (andesine, labradorite, and oligoclase), Fe-Ti oxides (titano-magnetite and titano-hematite), and accessory amphibole (kaersutite) and apatite. Whole-rock geochemistry data show little compositional variations in all the samples. The lavas present high Mg# (> 60), Cr, and Ni contents and low Nb and Zr contents. The trace element patterns suggest a common magma source with HIMU and EM1 affinities and OIB-like mantle signatures. The above-mentioned geochemical features indicate that the rocks originated from a low degree of partial melting at high pressures of different garnet peridotite source triggered, probably, by changes in mantle temperatures. The variation in composition of the lavas is controlled by variable degrees of partial melting, but possible subsequent enrichment processes can be envisaged. Some distinct magmatic processes “metasomatic events” occurred and affected the composition of the mantle source. In the nutshell, the genesis of melt beneath the Wakwa plain is dominated by a small-scale heterogeneous lithospheric mantle.

Some volcanic rocks from Nyiragongo volcano in the Democratic Republic of Congo contain highly oxidized olivine crystals. These olivines crystals are made of two phases, dark olivine on backscattered electron images of pure forsterite composition and grey Mg-poor areas made of olivine and iron-rich oxides. Calculation of the initial composition confirms that they are primary olivine with late separation of two different olivine compositions. Pure forsterite is enriched in SiO2 but contains lower amounts of CaO than Fe-rich areas, in agreement with expected partitioning of these elements related to the composition of the olivine. Iron-rich oxides formed around or inside the olivine crystals during the separation process and confirm a highly oxidized environment during their evolution. We propose that this separation occurred during subsolidus recrystallization under high fO2 conditions of the olivine crystals after cooling of the volcanic rocks. It provides evidences for circulation of iron-rich fluids or gas inducing deuteritic processes occurring in the large volcanic cone of the Nyiragongo, in relation with the presence of a shallow magma chamber connected to a large and permanent lava lake.

Alkaline basalts of Bafang and its environs are consisted of feldspars, olivines, pyroxenes and oxides which appear as phenocrysts, microphenocrysts and microcrysts.Feldspars are plagioclases Or 20.59-1.51 ) and anorthoclases ).Plagioclases are the most abundant amount these feldspars.Anorthoclases appear only in mugearite (BAF 3 and BAF 37) the most differentiated of the studied alkaline-basalts.In High Magnesian basalt, (HMg-B) plagioclases are labradorites (An 67.97-59.30Ab 38.74-30.43Or 2.75-1.60 ) and sanidine (An 45.44-31.82Ab 62.66-51.79Or 5.52-2.77), whereas in Low Magnesian basalt (LMg-B) there are labrador (An 67.4.75-51.96Ab 44.98-33.72Or 3.06-1.51), andesine (An 45.44-31.82Ab 62.66-51.79Or 5.52-2.77), oligoclase (An 26.65-15.84Ab 69.19-63.57Or 20.59-8.55 ) and anarthoclase (Ab 68.11-61.20Or 33.87-20.91An 10.98-4.93 ).Olivines are magnesian (Fo 86.7-50.1 ) and ferriferous (Fo 48.8-37.8 ).In HMg-B, olivine are only magnesian.These olivines are chrysolites and hyalositerite.In LMg-B, olivines are magnesian and ferriferous with the predominance of ferriferous.They are chrysolites, hyalositerite and hortonolite.Pyroxenes are Ca, Mg and Fe clinopyroxenes.There are diopsides (Wo 51.94-45.02En 44.41-33.16Fs 16.42-10.70) and augites (Wo 44.88-43.64En 41.03-37.04Fs 18.25-14.43).Oxides are magnetites represented by ulvos-

Quantifying water contents in the lithospheric mantle is key to our understanding of global geodynamics, mantle composition, and related physical properties. Most mantle lithologies (peridotite) contain little water (similar to 50 ppm), but petrological heterogeneities such as pyroxenites are more hydrous (similar to 300 ppm) relative to the mantle rocks. Pyroxenites also melt at lower temperatures than peridotites and are thus important to magma genesis. Thus, quantifying pyroxenite water contents provides new information on the distribution of water in the mantle. Here, we present phase-specific FTIR measurements of the water contents in pyroxenite mantle xenoliths from two continental lithospheric domains that experienced intense metasomatism: the French Massif Central (FMC, France) and the Adamawa Volcanic Plateau (AVP, Cameroon). The AVP garnet pyroxenites are more hydrated 9[H2O](Clinopyroxene) = 386-685 ppm; [H2O](Orthopyroxene) = 124-155 ppm; [H2O](Garnet) < 0.5 ppm) than FMC ones 9[H2O](Clinopyroxene) = 112-465 ppm; [H2O](Orthopyroxene )= 61-104 ppm; [H2O](Garnet) < 0.5 ppm). These water concentrations are homogenous at the grain and correlate with equilibrated major element concentrations, indicating that they are representative of lithospheric water, although the FMC pyroxenites were dehydrated during metasomatism by a carbonatitic fluid (based on the correlation between La-N/Sm-N and Ti/Eu ratios); the water contents of AVP pymxenites were likely not affected by metasomatism. FMC pyroxenites show peculiar FTIR spectra that may reflect the preferential dehydration of specific sites in the pyroxene structure. In both regions, metasomatism modified the light rare Earth element contents (e.g., Ce) of the pyroxenites, resulting in highly variable H2O/Ce ratios. Therefore, we conclude that the utility of the H2O/Ce ratio to identify the involvement of pyroxenites in magmas genesis is limited.

The axial fault-bounded depression of the South Kenya rift (SKR) locally displays anomalously wide sectors resulting from the presence of one (or many) elevated and offset block(s) on the flanks of the main trough. Very little attention has been paid so far to the nature of the driving mechanisms responsible for these atypical rift patterns. New insights are supplied by the Natron-Ol Doinyo Ogol rift segment at the southern extremity of the SKR, immediately north of the North Tanzanian Divergence (NTD). On the basis of interpreted SRTM-30 satellite imagery and Digital Elevation Models, our work allows us: i) to depict the highly-segmented arrangement of the similar to 7 Ma-lasted SKR system, ii) to establish a two-stage kinematic rift model that emphasizes the role of an inherited transverse discontinuity on the arrest, as well as lateral jump and off-axis development of anomalously-propagating rift structures, iii) to define the relative contribution of border vs inner fault networks to the total extension, which is estimated at 7-6 km (11.6-9.2%), and iv) to emphasize that inner faulting was not the dominant mode of strain accommodation during recent inward focussing of strain, and that no sharp transition exists from border fault- to intra-rift fault-dominated strain accommodation over time in the SKR immature rift system.