The Bay of Biscay and the Pyrenees correspond to a Lower Cretaceous rift system including both oceanic and hyperextended rift domains. The transition from preserved oceanic and rift domains in the West to their complete inversion in the East enables us to study the progressive reactivation of a hyperextended rift system. We use seismic interpretation, gravity inversion, and field mapping to identify and map former rift domains and their subsequent reactivation. We propose a new map and sections across the system illustrating the progressive integration of the rift domains into the orogen. This study aims to provide insights on the formation of hyperextended rift systems and discuss their role during reactivation. Two spatially and temporally distinct rift systems can be distinguished: the Bay of Biscay-Parentis and the Pyrenean-Basque-Cantabrian rifts. While the offshore Bay of Biscay represent a former mature oceanic domain, the fossil remnants of hyperextended domains preserved onshore in the Pyrenean-Cantabrian orogen record distributed extensional deformation partitioned between strongly segmented rift basins. Reactivation initiated in the exhumed mantle domain before it affected the hyperthinned domain. Both domains accommodated most of the shortening. The final architecture of the orogen is acquired once the conjugate necking domains became involved in collisional processes. The complex 3-D architecture of the initial rift system may partly explain the heterogeneous reactivation of the overall system. These results have important implications for the formation and reactivation of hyperextended rift systems and for the restoration of the Bay of Biscay and Pyrenean domains.

The Messinian salinity crisis (MSC) [Hsü et al., 1973] has deeply shaped the Mediterranean landscape and triggered large sedimentary deposits (evaporites and clastics) in the deep basins within a short time span. Until recently, the MSC has mainly been analyzed independently, either through outcrops located onshore (e.g. Morocco, Cyprus, Spain, Sardinia, Italy) or through marine seismic profiles in the deep offshore. Each approach bears its own limitations:(1) on the one hand, land outcrops refer to incomplete Messinian successions that are geometrically disconnected from the offshore Messinian deposits owing to tectonics (e.g. Apennines) and/or because they accumulated at an early stage of the crisis in shallow marginal basins (e.g. Spain); (2) on the other hand, seismic profiles from the upper margins down to the deep basins allow to image and explore the entire MSC event as a continuous process, but with a lower resolution and with a lack of stratigraphical and lithological control, in the absence of full recovery of scientific boreholes.We present here a synthesis of a set of modern geophysical data over the Mediterranean and Black seas allowing to image the Messinian markers (erosion surfaces, depositional units and their bounding surfaces) much better than previously and to study the spatio-temporal organisation of these markers from the inner-shelves down to the bathyal plains. The results from thirteen areas located offshore are compared, with common charts and nomenclatures. The comparative and multi-site approach developed here allows to analyse the record of the MSC on margin segments and basins that depict various structural, geodynamical and geological settings, to fix a number of local influencing factors (tectonics, subsidence, inherited topography, sedimentary fluxes...) and to partly assess their influence in facies and geometrical variations of the MSC units. We are thus able to extract from our analysis some recurrent signals related to the MSC ss., allowing us to discuss: (1) the amplitude and modalities of base-level changes during the MSC; (2) the depositional modalities of the MSC units in the deep basins; (3) the location of the erosion product of the margins and to emphasise (4) the major differences between the eastern and western Mediterranean basins. Une meilleure connaissance des enregistrements de la crise de salinité messinienne en domaine marin grâce à l'analyse sismique multi-sitesMots-clés. -Crise de salinité messinienne, Méditerranée, Profils sismiques, Evaporites, Erosion, Clastiques.Résumé. -La crise de salinité messinienne (CSM) [Hsü et al., 1973] a profondément modelé les paysages méditerra-néens et généré d'épaisses accumulations sédimentaires (évaporites et dépôts clastiques) dans les bassins profonds sur une brève période de temps à l'échelle géologique. Jusqu'à présent, la CSM a principalement été étudiée distinctement, à terre, grâce aux affleurements (ex. Maroc, Chypre, Espagne, Sardaigne, Italie…), et en domaine marin, par l'intermé-diaire de profils sismiques. Chacun...

On May 10th, 2018, an unprecedented long and intense seismic crisis started offshore, east of Mayotte, the easternmost of the Comoros volcanic islands. The population felt hundreds of events. Over the course of one year, 32 earthquakes with magnitude greater than 5 occurred, including the largest event ever recorded in the Comoros (Mw = 5.9 on May 15th, 2018). Earthquakes are clustered in space and time. Unusual intense long lasting monochromatic very long period events were also registered. From early July 2018, Global Navigation Satellite System stations and Interferometric Synthetic Aperture Radar registered a large drift, testimony of a large offshore deflation. We describe the onset and the evolution of a large magmatic event thanks to the analysis of the seismicity from the initiation of the crisis through its first year, compared to the ground deformation observation (GNSS and InSAR) and modelling. We discriminate and characterise the initial fracturing phase, the phase of magma intrusion and dike propagation from depth to the sub-surface, and the eruptive phase that starts on July 3rd, 2018, around fifty days after the first seismic events. The eruption is not terminated two years after its initiation, with the persistence of an unusual seismicity, whose pattern has been similar since summer 2018, including episodic very low frequency events presenting a harmonic oscillation with a period of ~16 s. From July 2018, the whole Mayotte Island drifted eastward and downward at a slightly increasing rate until reaching a peak in late 2018. At the apex, the mean deformation rate was 224 mm yr-1 eastward and 186 mm yr-1 downward. During 2019, the deformation smoothly decreased and in January 2020, it was less than 20% of its peak value. A deflation model of a magma reservoir buried in a homogenous half space fits well the data. The modelled reservoir is located 45 ± 5 km east of Mayotte, at a depth of 28 ± 3 km and the inferred magma extraction at the apex was ~94 m3 s-1. The introduction of a small secondary source located beneath Mayotte Island at the same depth as the main one improves the fit by 20%. While the rate of the main source drops by a factor of 5 during 2019, the rate of the secondary source remains stable. This might be a clue of the occurrence of relaxation at depth that may continue for some time after the end of the eruption. According to our model, the total volume extracted from the deep reservoir was ~2.65 km3 in January 2020. This is the largest offshore volcanic event ever quantitatively documented. This seismo-volcanic crisis is consistent with the trans-tensional regime along Comoros archipelago.

International audienceThe Bay of Biscay is bounded to the North by the North Biscay margin, which comprises the Western Approaches and Armorican segments. In the 1970s and 1980s, most researchers considered this margin typical of a non-volcanic passive margin: It is characterized by a striking succession of tilted blocks beneath which occurs the S reflector and the continent/ocean boundary is abrupt. This paper examines the Armorican segment and is based on a study of all early seismic profiles together with new multichannel reflection and refraction seismic data (NORGASIS cruise). An important result is the discovery of a 80-km wide Ocean-Continent Transition zone that coincides with the Armorican Basin (a deep sedimentary basin). It is characterized by a High-Velocity Layer-Crust (7.4-7.5 km/s) overlain by sediments. The other results are: i) the main crustal thinning occurs exclusively under the narrow continental slope. ii) The tilted blocks and the S-reflector are observed only at the base of the continental slope in the narrow domain called "neck area". iii) the North Biscay Ridge is a large oceanic plateau present only off the NW Armorican margin rather than a long ridge elongated off the whole North Biscay Margin

Volcanic eruptions are foundational events that shape the Earth's surface and provide a window into deep Earth processes. How the primary asthenospheric melts form, pond and ascend through the lithosphere is, however, still poorly understood. We document an on-going magmatic event offshore Mayotte Island (North Mozambique channel), associated with large surface displacements, very low frequency earthquakes and exceptionally deep (25-50 km) seismicity swarms. We present data from the May 2019 MAYOBS1 cruise, which reveal that this event gave birth to a 820m tall, ~ 5 km 3 deepsea volcanic edifice. This is the largest active submarine eruption ever documented. The data indicate that deep magma reservoirs were rapidly drained through dykes that intruded the entire lithosphere and that pre-existing subvertical faults in the mantle were reactivated beneath an ancient caldera structure.