A new chronostratigraphic framework for deep-sea volcaniclastic sedimentation in the Somali Basin provides key constraints on the timing, magnitude, and recurrence of explosive volcanism associated with the Comoros Archipelago over the past ~1.5 Myr. Multibeam bathymetry, high-resolution seismic reflection data, and seven sediment cores recovered north of the archipelago are combined to establish basin-scale correlations of volcaniclastic turbidites. Temporal control is achieved through tuning of oxygen isotope stratigraphies.Seismic–core correlations reveal multiple regionally extensive event deposits, with individual layers covering minimum areas ranging from ~20 km² to more than 130,000 km². Petrographic observations and geochemical analyses show that the turbidites are dominated by basaltic to trachybasaltic glass fragments (sideromelane and tachylite), consistent with a Comorian volcanic provenance. The large volumes, widespread dispersal, and sharp basal contacts of these deposits support direct syn-eruptive emplacement by eruption-fed sediment gravity flows, rather than post-eruptive remobilization. Such deposits require highly energetic explosive activity, consistent with Surtseyan to (sub-)Plinian eruptions capable of generating large quantities of pyroclastic material and transporting it hundreds of kilometers into the deep basin.The resulting chronostratigraphy documents recurrent phases of intensified volcaniclastic sedimentation at ~1.63–1.35 Ma, ~1.03–0.72 Ma, and ~0.40–0.13 Ma, indicating episodic but long-lived explosive volcanism in the Comoros region during the Quaternary. These findings highlight the Comoros Archipelago as a major center of explosive basaltic volcanism in the western Indian Ocean and underscore the importance of deep-marine sedimentary records for assessing the frequency, magnitude, and hazard potential of large-scale submarine eruptions.

The Western Mediterranean is constituted by a series of back-arc basins that opened in response to the African slab rollback throughout the Alpine orogenies. The Ligurian Basin occupies the northeastern termination of this realm and resulted from the rifting and subsequent drift of the Corsica-Sardinia block, between Oligocene and Burdigalian-Langhian times, coevally with the neighbouring Western Alpine collision. The nature of its basement, beneath thick sedimentary deposits, has long remained elusive. The SEFASILS cruise acquired deep penetrating wide angle seismic data from densely deployed ocean bottom sensors, as well as long offset reflection and gravity data. The obtained tomographic images unequivocally reveal a large expanse of exhumed mantle flooring the northern half of the basin beneath basinal deposits. Further south, intermediate crustal velocities are found and the nature of the basement is more ambiguous. Using satellite-derived gravity measurements and taking into account the documented kinematics of the main phase of the Ligurian opening, we show that most of the seafloor—if not all—is indeed of oceanic origin and that the observed mantle tract was emplaced from an accretion centre inside the basin rather than from under the flanking margin. In particular, the extinct spreading axis is revealed by free-air gravity anomalies. These results thus show that, albeit significant opening rates of ~4 cm/yr or more are inferred here, seafloor spreading consisted essentially in mantle unroofing with little to no melt production. Moreover, a domain of ultrathinned continental crust is also evidenced at the toe of the northern margin, that is evocative of some ductile-dominant deformation immediately prior to breakup. Mantle exhumation seems to have occurred successively and somewhat continuously throughout the basin formation on opposite-verging continental and oceanic detachment systems, active prior to and after breakup respectively.

The exact nature of crustal magmatic reservoirs is elusive as they cannot be sampled in situ. The traditional view that magma chambers contain essentially molten material has recently been replaced by the transcrustal magmatic system (TCMS), in which reservoirs are mostly composed of immobile magmatic crystals with a minute fraction of more mobile melt1-3, creating a 'magmatic mush'3. Eruptions are possible if a significant portion of melt segregates into melt-rich lenses within the mush reservoir1-3. The TCMS concept is, however, a default model essentially justified by the absence of clear geophysical signatures of melt-rich magma chambers1,4, and by the rare and tentative estimates of the melt fraction in the crustal storage zones based on geochemical and textural analysis of eruptive products5,6. Here we image a bright electrical conductor at 23 ± 1 km below sea level beneath Mayotte island that we interpret as a magmatic reservoir, based on laboratory measurements of Mayotte's melt conductivity. This large magmatic reservoir (more than 200 km3) contains a high melt fraction (22-42%). Such a crystal-to-liquid ratio matches the reconstructed differentiation paths7-9 producing the melts that recently erupted at Mayotte. This reservoir is possibly connected to the system that fed the large submarine eruption of Fani Maoré in 2018-201910.

The hyper-extended Eastern Sardinian margin is due to the eastward migration of the Appennine-Calabria subduction zone, creating the Neogene back-arc Tyrrhenian Basin. This area was affected by strong erosion during the Messinian Salinity Crisis (MSC, 5.97 - 5.33 Ma) on the continental shelf and slope leading to a major discontinuity, known as the Messinian Erosion Surface (MES), constituting, therefore, a remarkable stratigraphic marker. It is also a powerful paleo-topographic marker of the MSC times and can be used as a marker of the deformation during Plio-Quaternary times. The end of the rifting phase in the Eastern Sardinian margin is dated during the Tortonian (11.63 - 7.25 Ma) attested by the occurrence of a relatively thick syn- and post-rift sequence pre-dating the MES.The “METYSS 4” cruise led to the acquisition of more than 2,000 km of very high-resolution (VHR) seismic reflection data, following a dense grid, on the Eastern Sardinian continental shelf and slope, which has been little explored until now. Seismic interpretation allowed for mapping the major erosion surface, the MES, across the continental shelf and slope. At the base of the PQ sequence, the MSC paleo-topography highlights a hydrographic paleo-network identical to the current one and a general progradation of the shelf-break toward the east during the Plio-Quaternary. In the southern part of the study area, several east-dipping normal faults, oriented N-S, significantly shift the MES (between 5 and 55 m; assuming sound wave velocity of 1700 m/s in Plio-Quaternary sediments). The MES is tilted toward the fault and is covered by Plio-Quaternary deposits, which display a fan-shaped geometry (eg. 50 m thick on the hanging wall). These NS-trend faults are cross-cut by E-W trending messinian canyon and this fault pattern is also observed on the other flank of the canyon. The along-strike geomorphological analysis of canyons reveals the occurrence of knickpoints (slope breaks) coinciding with the front of the two fault patterns. Moreover, the shifts in water depth of most knickpoints are at the same order of amplitude than fault offsets (ie. 10 to 50 m). These geomorphologic markers reinforce the hypothesis that the fault activity is recent (ie. less than 5 Ma). We interpret these observations as markers of a recent reactivation of the structures inherited from the rift in the western part of the Tyrrhenian Sea.

The Comoros archipelago located in the western Indian Ocean has been a topic of debate for ca. 50 years regarding its origin. Various mechanisms have been proposed to explain its formation, ranging from the impact of a mantle plume to the development of a plate boundary between the Somalia and Lwandle plates. Determining the timing of the volcanic activity is crucial to understanding the archipelago's origin. Despite recent geochronological studies, the age of the initial volcanic eruptions on the islands remains uncertain due to the difficulty of accessing the earliest lavas. This study uses high- quality seismic reflection profiles and regional stratigraphy to identify the first volcanic series that marked the onset of volcanism on each island of the Comoros Archipelago. Our findings reveal that localized volcanic activity began ca. 32 Ma at Z & eacute;l & eacute;e and Geyser banks and Mayotte edifice, the eastern portions of the archipelago, much earlier than previously believed. Volcanism spread across the Comoros archipelago ca. 9-8 Ma, from the northern part of the Mayotte edifice to Moh & eacute;li Island in the west. Ca. 4 Ma, volcanic activity occurred on Anjouan Island and the Jumelles seamounts, followed by Grande Comore Island ca. 2 Ma. This progression of ages from east to west indicates a chronological sequence over time. The timing of volcanic activity in the Comoros archipelago is similar to the magmatism evolution documented at Madagascar and along the East African Rift System (EARS). Magmatic activity began in the late Oligocene, followed by quiescence during the middle Miocene, and resumed in the late Miocene, coinciding with widespread deformation along the EARS, including its offshore branches and Madagascar. Our study shows that the regional tectonic control of volcanic activity in the Comoros archipelago began during the early Miocene, thereby suggesting that the Comoros archipelago developed as an offshore branch of the EARS south of the Somalian plate at that time.

This paper aims to solve the longstanding debate on the origin of the Comoros volcanic archipelago (Mozambique Channel, Indian Ocean) concerning whether it represents a hotspot trail or a boundary between the Lwandle and Somalia plates in possible connection with the East African Rift System (EARS). To achieve this goal, we analyzed rock samples from recently discovered and previously uninvestigated volcanoes and edifices by means of geochemistry and geochronology. Major-trace element analyses and radiometric dating (Ar-40/Ar-39, K-Ar, and (U-Th)/He) allow us to identify a widespread phase of Comorian volcanism initiated at 9-8 Ma, involving the Z & eacute;l & eacute;e, Geyser, and Leven banks, three atolls east of the Comoros. Another tectono-magmatic phase initiated at 2.5 Ma led to a N-S widening of seamount volcanism, and to the progressive development of en-& eacute;chelon NW-SE structures. With this new addition of atolls and seamounts, the Comoros Archipelago becomes a similar to 700 km-long, similar to 200 km-wide E-W chain extending from the Cenozoic volcanoes of Madagascar to the EARS. The reactivation of this chain at 9-8 and 2.5 Ma coincides with abrupt changes in the motion of the Somalia plate relative to the Lwandle plate, and with plate boundary modifications. The en-& eacute;chelon reorganization of structures also matches the kinematic evolution of Somalia relative to Lwandle, from transtension (>3 Ma) to pure dextral slip (<= 3 Ma) in the northern Mozambique Channel. We conclude that the Madagascar-Comoros volcanic chain is a branch of the EARS and a plate boundary, further strengthening the link between magmatism and the Rovuma-Lwandle-Somalia plate kinematics.

The 2018-2021 Fani Maore submarine eruption (offshore of Mayotte, Mozambique Channel) extruded a bulk volume of similar to 6.5 km(3) of basanite magma onto the seafloor at a depth of 3300 m, with effusion rates ranging from 150 to 200 m(3)/s in the first year of the eruption, to less than 11 m(3)/s in the final months. Six oceanographic campaigns provided a large sample set covering the entire flow field at high spatial and temporal resolution. These samples allow us to precisely track syn-eruptive degassing processes through quantification of textural parameters including porosity, pore connectivity, vesicle number density (NV) and vesicle size distributions (VSD). Three different textural facies have been distinguished. (1) Vesicular lavas (average porosity of 35%) display unimodal VSDs, high NV (14-214 mm(-3)), and small and spherical vesicles. (2) Lavas with intermediate porosities (25%) have scarce small vesicles, VSDs shifted towards larger vesicles, and low NV (0.2-39 mm(-3)). (3) Dense lavas with low porosities (14%) display bimodal VSDs distribution, a dominant mode of small vesicles, and low NV (0-87 mm(-3)). The early phase of activity (Phase 1, June 2018 - May 2019) built the main edifice and was fed by rapid ascent and closed-system degassing of volatile-rich magma ascending from a deep reservoir to the seafloor (Facies 1). Distal samples collected from lava flows emitted during Phase 2, between June and July 2019, show large and irregular shape vesicles mostly related to bubble growth and coalescence, and outgassing during emplacement (Facies 2). These lavas are interpreted to be emplaced during extension of a lava tube system which began to develop during Phase 1. The final phase (Phase 3, August 2019 - January 2021) was associated with lava effusion located at the northwest lava flow front, 6 km from the summit. Phase 3 involved a more degassed magma due to the increase in the length of the magma pathway (Facies 3). Phase 3 lavas were also extremely outgassed and associated with construction of a new complex lava flow field with tumuli and multiple ephemeral vents (lava breakouts). The heterogeneous textures within the studied samples reflect changing ascent and effusion rates with time, leading to emplacement of lava flows which varied depending on the degree of degassing and effusion rate. We conclude that emplacement of the Fani Maore large submarine lava flow fields developed through extensive and prolonged tube systems this being supported by the high effusion rates.

The 2018–2021 Fani Maoré submarine eruption (offshore of Mayotte, Mozambique Channel) extruded a bulk volume of ∼6.5 km3 of basanite magma onto the seafloor at a depth of 3300 m, with effusion rates ranging from 150 to 200 m3/s in the first year of the eruption, to less than 11 m3/s in the final months. Six oceanographic campaigns provided a large sample set covering the entire flow field at high spatial and temporal resolution. These samples allow us to precisely track syn-eruptive degassing processes through quantification of textural parameters including porosity, pore connectivity, vesicle number density (NV) and vesicle size distributions (VSD). Three different textural facies have been distinguished. (1) Vesicular lavas (average porosity of 35%) display unimodal VSDs, high NV (14–214 mm−3), and small and spherical vesicles. (2) Lavas with intermediate porosities (25%) have scarce small vesicles, VSDs shifted towards larger vesicles, and low NV (0.2–39 mm−3). (3) Dense lavas with low porosities (14%) display bimodal VSDs distribution, a dominant mode of small vesicles, and low NV (0–87 mm−3). The early phase of activity (Phase 1, June 2018 – May 2019) built the main edifice and was fed by rapid ascent and closed-system degassing of volatile-rich magma ascending from a deep reservoir to the seafloor (Facies 1). Distal samples collected from lava flows emitted during Phase 2, between June and July 2019, show large and irregular shape vesicles mostly related to bubble growth and coalescence, and outgassing during emplacement (Facies 2). These lavas are interpreted to be emplaced during extension of a lava tube system which began to develop during Phase 1. The final phase (Phase 3, August 2019 – January 2021) was associated with lava effusion located at the northwest lava flow front, 6 km from the summit. Phase 3 involved a more degassed magma due to the increase in the length of the magma pathway (Facies 3). Phase 3 lavas were also extremely outgassed and associated with construction of a new complex lava flow field with tumuli and multiple ephemeral vents (lava breakouts). The heterogeneous textures within the studied samples reflect changing ascent and effusion rates with time, leading to emplacement of lava flows which varied depending on the degree of degassing and effusion rate. We conclude that emplacement of the Fani Maoré large submarine lava flow fields developed through extensive and prolonged tube systems this being supported by the high effusion rates.

Summary When interpreting marine Very High-Resolution (VHR) single-channel seismic reflection data, the signal in the water-column is generally considered as noise and is often eliminated by a water-mute application to focus on geological information under the seafloor. Alternatively, the signal in the water-column can be used to study ocean currents or gas/fluid emissions. To provide images of the sedimentary formations and tectonic structures beneath the seafloor in shallow water regions, such as continental shelves and lakes, marine seismic reflection profiles are often acquired using a single-channel streamer and sparker-type source, providing VHR data, with limited penetration-depth. To exploit the full potential of these single-channel data, we propose a simple algorithm, called REWARE (Recovery of Water-column Acoustic Reflectors). This algorithm allows to extract further geological information from the water-column data using open-source codes (Seismic Un*x), adding the coherent signal from the previous shots, recorded in the water-column, to the previous traces. The record length becomes longer while maintaining a very high trace-to-trace consistency. To demonstrate its efficiency, we present two examples of the REWARE processing in two different geological contexts: the East Sardinia shelf (Italy) and the North Evia Gulf (Greece). This method provides deeper images than with original data for seismic data acquired across steep slopes, such as canyons or continental shelf breaks. Thus, depending on the seafloor geometry and sub-seafloor structures, it is possible to image or map sediment layers and tectonic structures at depth, keeping a very high structural resolution.

Abstract. In this study, alternatively to the megathrust, we identify upper plate normal faults orthogonal to the trench as a possible tsunami source along the Lesser Antilles subduction zone. We study the Morne Piton Fault system, a trench-perpendicular upper crustal fault affecting the Lesser Antilles forearc at the latitude of Guadeloupe. By the means of seismic reflection, high resolution bathymetry, Remotely Operated Vehicle images and dating, we reassess the slip rate of the Morne Piton Fault at 0.2 mm.yr-1 since fault inception (i.e. 7 Ma), dividing by five previous estimations and thus increasing the earthquake time recurrence and lowering the associated hazard. We evidence a metric scarp with striae at the toe of the Morne Piton Fault system suggesting a recent fault rupture. We estimate a fault rupture area of ~ 450–675 km2 and then a magnitude range for the seismic event around Mw 6.5 ± 0.5. We present results from a multi-segment tsunami model representative for the worst-case scenario which gives an overview of what could happen in terms of tsunami generation if the whole identified Morne Piton Fault segments ruptured together. Our model illustrates the potential impact of local tsunamis on the surrounding coastal area as well as local bathymetric controls on tsunami propagation as (i) shallow water plateaus act as secondary sources and are responsible for a wrapping of the tsunami waves around the island of Marie-Galante, (ii) canyons are focusing and enhancing the wave height in front of the most touristic and populated town of the island, (iii) a resonance phenomenon is observed within Les Saintes archipelago showing that the waves’ frequency content is able to perturbate the sea-level during many hours after the seismic rupture.

In this study, alternatively to the megathrust, we identify upper-plate normal faults orthogonal to the trench as a possible tsunami source along the Lesser Antilles subduction zone. The Morne Piton fault system is such a trench-perpendicular upper crustal fault at the latitude of Guadeloupe. By means of seismic reflection, high-resolution bathymetry, remotely operated vehicle (ROV) imaging and dating, we reassess the slip rate of the Morne Piton fault since 7 Ma, i.e., its inception, and quantify an average rate of 0.25 mm yr-1 since ca. 1.2 Ma. This result divides by two previous estimations, increases the earthquake time recurrence and lowers the associated hazard. The ROV dive revealed a metric scarp with striae at the toe of the Morne Piton fault system, suggesting a recent fault rupture. We estimate a fault rupture area of similar to 450-675 km2 and then a magnitude range for a maximum seismic event around Mw 6.5 +/- 0.5, making this fault potentially tsunamigenic as the nearby Les Saintes fault responsible for a tsunami following the 2004 Mw 6.3 earthquake. Consequently, we simulate a multi-segment tsunami model representative of a worst-case scenario if all the identified Morne Piton fault segments ruptured together. Our model provides clues for the potential impact of local tsunamis on the surrounding coastal area as well as for local bathymetric controls on tsunami propagation. We illustrate that (i) shallow-water plateaus act as secondary sources and are responsible for a wrapping of the tsunami waves around the island of Marie-Galante; (ii) canyons indenting the shallow-water plateau slope break focus and enhance the wave height in front of the most touristic and populated town of the island; and (iii) the resonance phenomenon is observed within the Les Saintes archipelago, showing that the waves' frequency content is able to perturb the sea level for many hours after the seismic rupture.

We shed light on the nature and structure of the crust surrounding the Comoros Archipelago, western Indian Ocean, offering insights into the region ' s geological history and volcanic island formation. Our comprehensive study encompasses the acquisition of new, deeply penetrating seismic data from the SISMAORE cruise (refraction and reflection seismic), and the subsequent analysis of the characteristics and structure of the crust surrounding the Comoros Archipelago. Both the reflection seismic imaging and the velocity structure using ocean bottom seismometers indicate that the crust of the Comoros Basin exhibits oceanic characteristics, thus resolving previous controversies about its nature. The thickness of the oceanic crust ranges from 5.8 to 6.6 km in the north of the archipelago to 6 - 7.2 km within the Comoros Basin. The estimated roughness of the top basement in the Comoros Basin ranges from 110 to 200 m values typical of intermediate to slow spreading ridges, such as the extinct spreading centre in the West Somali Basin. The unloaded basement depth of the Comoros Basin closely matches the expected water-loaded subsidence for a Cretaceous or Jurassic oceanic lithosphere. In contrast, the West Somali Basin to the north of the Comoros Archipelago has shallower basement depths, potentially linked to recent volcanic activity along the archipelago. We propose that the pre-existing oceanic fracture zones in the West Somali Basin underwent reactivation, first during the Turonian period and later during the Late Eocene. These reactivated fracture zones may have acted as preferred pathways for the emplacement of the volcanic islands of the Comoros Archipelago. The EW trend of the archipelago appears to follow a marked change in the direction of these reactivated fracture zones, suggesting that the associated lithospheric weakening likely played a critical role in facilitating the formation of the Comoros Archipelago.

By demonstrating that extensional inheritance plays a decisive role in the formation of orogens, recent studies have questioned the ability of a unique, complete Wilson cycle model to explain the diversity of collisional orogens. For 5 years, the OROGEN Research Project had therefore the ambition to challenge this classical Wilson cycle model. By focusing on the diffuse Africa-Europe plate boundary in the Biscay-Pyrenean-Western Mediterranean system, the project questioned the preconceived "Orogen singularity" assumption and investigated the role of divergent and convergent maturities in orogenic and post-orogenic processes. This work led us to rethink the development of collisional orogens in a genetic (or process-driven) way and to propose an updated version of the " classical Wilson cycle", the Wilson Cycle 2.0, and the ORO-Genic ID concept presented in this paper. The particularity of the Wilson Cycle 2.0 is to take into account the divergence and convergence maturity reached during extensional and orogenic processes in proposing different tectonic tracks associated with different ORO-Genic ID numbers. The ORO-Genic ID is composed of a letter (or track), corresponding to the maturity of divergence reached and a number corresponding to the maturity of convergence reached during the formation of the orogen. This new concept relies on the observed pre- and syn- convergent tectono- stratigraphic and magmatic record and deformation history and can be identified in using diagnostic criteria presented in this paper. It represents therefore a powerful tool that can be used to characterize the evolution and the architectural type of an orogenic system. Moreover, as a mappable concept, it can be easily used worldwide and can help us to explain differences in the style of deformation at crustal scale between orogens. En d & eacute;montrant que l'h & eacute;ritage extensional joue un r & ocirc;le d & eacute;cisif dans la formation des orog & egrave;nes, des & eacute;tudes r & eacute;centes ont remis en question le cycle de Wilson et sa capacit & eacute;, en tant que mod & egrave;le unique, & agrave; expliquer la diversit & eacute; des orog & egrave;nes collisionnels. Pendant 5 ans, le projet de recherche OROGEN s'est donc donn & eacute; pour ambition de questionner ce mod & egrave;le classique du cycle de Wilson. En se concentrant sur la fronti & egrave;re diffuse entre les plaques Afrique-Europe dans le syst & egrave;me Golfe de Gascogne-Pyr & eacute;n & eacute;es-M & eacute;diterran & eacute;e occidentale, le projet a remis en cause l'hypoth & egrave;se pr & eacute;con & ccedil;ue de la << singularit & eacute; orog & eacute;nique >> et a explor & eacute; le r & ocirc;le de la maturit & eacute; divergente et de la maturit & eacute; convergente dans les processus orog & eacute;niques et post-orog & eacute;niques. Ce travail nous a amen & eacute;s & agrave; repenser le d & eacute;veloppement des orog & egrave;nes collisionnels d'un point de vue g & eacute;n & eacute;tique (ou ax & eacute; sur les processus) et nous a amen & eacute; & agrave; proposer une version actualis & eacute;e du << cycle de Wilson classique >>, appel & eacute;e Cycle de Wilson 2.0 et le concept d'ID ORO-g & eacute;nique pr & eacute;sent & eacute; dans cet article. La particularit & eacute; du Cycle de Wilson 2.0 est de prendre en compte la maturit & eacute; de la divergence et la maturit & eacute; de la convergence atteinte au cours des processus d'extension et d'orog & eacute;n & egrave;se, en proposant diff & eacute;rents parcours tectoniques associ & eacute;s & agrave; diff & eacute;rents num & eacute;ros d'identit & eacute; ORO-g & eacute;nique. Le num & eacute;ro d'identit & eacute; ORO-g & eacute;nique est compos & eacute; d'une lettre (ou d'un parcours), correspondant & agrave; la maturit & eacute; de la divergence atteinte, et d'un num & eacute;ro correspondant & agrave; la maturit & eacute; de la convergence atteinte lors de la formation de l'orog & egrave;ne. Ce nouveau concept repose sur l'enregistrement tectono-stratigraphique et magmatique avant et pendant la phase de convergence, ainsi que sur l'histoire de la d & eacute;formation observ & eacute;e, et peut & ecirc;tre identifi & eacute; en utilisant les crit & egrave;res diagnostiques pr & eacute;sent & eacute;s dans cet article. Il constitue donc un outil puissant pouvant & ecirc;tre utilis & eacute; pour caract & eacute;riser l'& eacute;volution et le type architectural d'un syst & egrave;me orog & eacute;nique. De plus, en tant que concept cartographiable, il peut & ecirc;tre facilement utilis & eacute; dans le monde entier et nous aider & agrave; expliquer les diff & eacute;rences de style de d & eacute;formation & agrave; l'& eacute;chelle crustale entre les orog & egrave;nes.

. The “Fani Maoré” eruption o ff the coasts of Mayotte has been intensively monitored by applying methods similar to those used for subaerial eruptions. Repeated high-resolution bathymet-ric surveys and dredging, coupled with petrological analyses of time-constrained samples, allowed tracking the evolution of magma over the whole submarine eruptive sequence. Indeed, after one year of direct ascent (Phase 1), basanitic magma switched to a di ff erent pathway that sampled a tephri-phonolitic subcrustal reservoir (Phase 2). Later, the magma pathway shifted again in the crust result-inginaneweruptionsitelocated6kmnorthwestofthemainedifice(Phase3).Thepetrologicalsigna-ture of lava flows reveals both an evolution by fractional crystallization and syn-eruptive mixing with a tephri-phonolitic magma. We demonstrate that high-flux eruption of large volumes of basanitic magma from a deep-seated reservoir can interact with shallower reservoirs and remobilize eruptible magma. This has significant hazards implications with respect to the capacity of such large eruptions to reactivate shallow-seated inactivereservoirsfromatranscrustalmagmaticsystemthatcouldbelocatedpotentiallyatadistance from the high-flux eruptive site.

Geophysical and geological data from the North Mozambique Channel acquired during the 2020–2021 SISMAORE oceanographic cruise reveal a corridor of recent volcanic and tectonic features 200 km wide and 600 km long within and north of Comoros Archipelago. Here we identify and describe two major submarine tectono-volcanic fields: the N’Droundé province oriented N160°E north of Grande-Comore Island, and the Mwezi province oriented N130°E north of Anjouan and Mayotte Islands. The presence of popping basaltic rocks sampled in the Mwezi province suggests post-Pleistocene volcanic activity. The geometry and distribution of recent structures observed on the seafloor are consistent with a current regional dextral transtensional context. Their orientations change progressively from west to east (∼N160°E, ∼N130°E, ∼EW). The volcanism in the western part appears to be influenced by the pre-existing structural fabric of the Mesozoic crust. The 200 km-wide and 600 km-long tectono-volcanic corridor underlines the incipient Somalia–Lwandle dextral lithospheric plate boundary between the East-African Rift System and Madagascar. Supplementary Materials: Supplementary material for this article is supplied as a separate file: crgeos-159-suppl.pdf Des données géophysiques et géologiques ont été acquises lors de la campagne océanographique SISMAORE (2020–2021). Deux grands champs tectono-volcaniques sous-marins ont été découverts tout le long et principalement au nord de l’archipel des Comores : la province N’Droundé orientée N160°E au nord de Grande-Comore, et la province Mwezi orientée N130°E au nord d’Anjouan-Mayotte où des roches basaltiques de type popping-rocks suggèrent une activité volcanique possiblement actuelle à pléistocène. La géométrie et la distribution des structures récentes sont cohérentes avec un contexte régional actuel transtensif dextre. Leurs orientations évoluent d’Ouest en Est (∼N160°E, ∼N130°E, ∼EW), suggérant pour la partie occidentale, une mise en place du volcanisme influencée par la structuration crustale préexistante. Le corridor tectono-volcanique de 200 km de large et de 600 km de long dessine une limite de plaque lithosphérique Somalie-Lwandle immature en décrochante dextre entre le système du rift est-africain et Madagascar. Compléments : Des compléments sont fournis pour cet article dans le fichier séparé : crgeos-159-suppl.pdf

&lt;p&gt;The Eastern Sardinian margin consists in a hyper-extended rifted margin, located in the western Tyrrhenian Sea, a recent back-arc basin (late Neogene). This area was affected by strong aerial erosion during the Messinian Salinity Crisis (MSC, 5.96 &amp;#8211; 5.33&amp;#160;My) associated with the drop of sea level (&gt; 1500&amp;#160;m) which occurred throughout the whole Mediterranean. The Gulf of Orosei and surrounding offshore areas are characterized by small and diffuse drainage systems input, where the Messinian Erosion Surface (MES) has rarely been studied while it has been in large fluvial systems (Rhone, Ebro). The MES was already found in the Cendrino valley (which flows in the Gulf) and in the East-Sardinia Basin but the link between onshore and offshore was never been studied in the area. The &amp;#8220;METYSS 4&amp;#8221; cruise (June 2019, R/V &amp;#8220;T&amp;#233;thys II&amp;#8221;) allowed acquiring more than 2000 km of very high-resolution (VHR) seismic data (Sparker), following a dense grid (1.5 km average profile spacing), on the Eastern Sardinian continental shelf, and especially in the Orosei Gulf area, that has been little explored until now. While the main limitation on seismic data (air-gun) interpretation is often due to the occurrence of sea bottom multiple, the limitation for Sparker data may also be due to very short shot intervals at greater water depth. The seismic trace ends where there still is signal of interest. Thus, we applied a simple method to increase investigation depth for short shot intervals (0.333 - 0.533&amp;#160;ms), which allowed interpretation on the continental slope. This approach consists in copying the raw data and concatenating the copied data under the raw data with a shift of 1 shot point. To constrain the MES depth on the continental slope and shelf we compared air-gun seismic data from previous METYSS surveys, where the MES has already been interpreted by a strong erosional discordance between Plio-Quaternary deposits and pre-MSC units, with the new VHR data. The restoration of the morphological features of the Orosei canyon at Messinian times shows that the former Messinian canyon network is very similar to the present-day one. The present-day canyon and its tributaries show sub-marine erosion in the talwegs. The heads of the canyons present gravitational features, highlighted by chaotic deposits near the talweg of the canyon or in-between the Plio-Quaternary strata. Offshore Arbatax, south Orosei, the seismic profiles show no significant Plio-Quaternary deposits (thickness &lt; 0.1&amp;#160;sTWT), which allows polygenic pre-MSC units to occur at the seafloor. In the Gulf, we observe thick deposits (0.4 - 0.5&amp;#160;sTWT) on the right bank of Orosei Canyon, making it more complicated to image the MES in this area. The sedimentation rate on this margin is very low (&lt;em&gt;c.a.&lt;/em&gt; 9&amp;#160;cm/ka in the Gulf of Orosei), which is consistent with previous studies on the East-Sardinian basin (3-20&amp;#160;cm/ka). These preliminary results will allow correlating for the first time the MES distribution from the onshore to the offshore continental slope of the Eastern Sardinian Margin in order to improve the MSC understanding in this key area.&lt;/p&gt;

The Central English Channel troughs correspond to elongated incisions up to 250 m-deep, at several locations at the bottom of this sea corridor. Depending on their location, they are usually interpreted as part of the submerged quaternary paleovalley network or as resulting from megaflood events. Shedding light on these features, their age, and the processes underlying their development is key for understanding their significance in terms of event geology. The interpretation of a dense grid of high-resolution marine seismic data acquired in the Bay of Seine area reveals that the extensive Quaternary paleovalley and trough network commonly as associated to the “Channel River” system is actually subdivided into at least two superimposed and unrelated incised networks. The overlying network corresponds to fluvial incisions developing during low sea-level conditions of Pleistocene time and connects to the present day fluvial network. The underlying network corresponds to the troughs and appears as a complex, deeper, relatively discontinuous and isolated network. This older network shows unexpected local incision depth up to c.350-400 m-deep and complex sedimentary infill involving several sedimentary processes and environments from fluvial to tidal and shallow-marine. We discuss these observations and their implications for understanding the origin, age and development of the troughs all over the English Channel, from the Dangeard Troughs in the Dover Strait to the Hurd Deep at the western end. We also raise questions about the significance of these large incised features in terms of source-to-sink system of northwestern Europe.

Phylogenetic studies of present-day terrestrial organisms suggest that faunal dispersals between South America and the Greater Antilles may have occurred during the Cenozoic through the Lesser Antilles. However, because of the lack of geological data to unravel the areas that may have emerged along the Lesser Antilles trench, the migration paths used by their ancestors remain unknown. Here, we present novel paleogeographic maps of the central Lesser Antilles (extending from Guadeloupe to Martinique islands) which are built on the basis of onshore and offshore stratigraphic correlations (50 seismic lines, biostratigraphy of 9 dredged and 29 field samples, six sedimentary logs). We find that repetitive episodes of uplift and drowning have occurred in the central part of the Lesser Antilles during the Neogene. Offshore, the Marie-Galante Basin comprises three sedimentary megasequences that deposited between: (i) the Oligocene and Early Miocene, including the extinct arc, (ii) the Middle and Late Miocene and (iii) the latest Miocene and Holocene. These sediments infill a NNW-SEE trending forearc rift that opened during the Early Miocene. The megasequences are separated by subaerial regional unconformities that affect the rift shoulders. Onshore, we show that the lower part of the carbonate platform in Guadeloupe and La Désirade has deposited during the late Messinian. In Martinique, we refine the age of the carbonate deposits belonging to the extinct arc to the Chattian-Burdigalian, and evidence a major subaerial unconformity corresponding to the Middle Miocene. We propose that between Anguilla and Martinique, from north to south, large archipelagos, which are now drowned, have existed during the early Middle Miocene and the latest Miocene. We suggest that during the Miocene, the Lesser Antilles may have been used as a pathway for land-faunal dispersals from South America.