In global geodynamics, one of the most striking events is the transition from continental rifting to oceanic spreading, as most of the involved parameters fundamentally change (rift to drift, mantle source of magmas, nature of the lithosphere, magmatic plumbing system architecture, hydrothermal system). Despite their importance for the Earth geodynamics, the processes that govern the initiation of oceanic spreading and the associated production of juvenile magmatic crust remain first order open questions for the international geo-community. Few quantitative constraints exist on how magmatic spreading initiates to form steady MOR? In other words: How and when typical magmato/tectonic processes of oceanic spreading are gradually emplaced during Ocean Continent Transition (OCT) stage? Ultimately, why, at a certain moment, continental thinning switch to magmatic accretion and initiates the break-up? These fundamental questions could be tackled either by models (numerical or analogic) or following quantitative documentation of processes on fossil OCT and/or on active mature rifts, that can be viewed as nascent MOR. The Afar region at the northern end of the East African Rift system is the unique place on Earth where magmatic continental rifting and associated ongoing break-up processes are exposed onshore. This magmatic rift system is dissecting a Large Igneous Province and is connected laterally to the Red Sea and Gulf of Aden oceanic spreading ridges. This system presents the key advantage to expose extensional structures considered at ocean-continent transition with magmatic segments characterized by contrasted morphologies, magmato-tectonic styles, and maturity that have tentatively been assimilated to proto-spreading centers. The main working hypothesis of this project is that Afar is presently experiencing the final stage of continental break-up and progressive onset of steady magmatic spreading (process already completed in the lateral Red Sea and Gulf of Aden). The three main active, contrasted and complementary magmatic segments of Afar (Erta Ale, Dabbahu-Manda Hararo, Assal) offer the opportunity to study mantle and crustal processes in order to decipher fundamental parameters that control focussing of tectonic and magmatic activity until complete removal of continental lithosphere. The MAGMAFAR project is designed to make a breakthrough into this key and first order fundamental scientific issue of continental break-up in magmatic context, and rift transition to the onset of MOR. We will particularly focus on: (i) how do magmatic and tectonic processes control the styles and morphologies of magmatic segments? what are the parameters responsible for the characteristics of proto, steady-state spreading processes? (ii) why and how stable magma production and organized/focussed transfer to the crust start and led to break-up? Along the active magmatic segments of Afar we still need to understand precisely: how magmas are generated? how they are transferred to the crust? how they interact and are controlled by other forcing parameters (in particular, the mechanical behavior of the lithosphere)? We elaborated a general strategy that will combine high resolution quantification of both tectonic and igneous processes in the (i) active and (ii) plio-quaternary natural systems, which will serve in turn to calibrate (iii) an integrated thermo-mechanical modelling. Such an integrated and multidisciplinary approach, based on the combination of numerous complementary skills (petrology / geochemistry / geochronology / remote-sensing / structural geology / thermomechanical modelling), will be focused on the comprehensive description of these unique active segments, in order to bridge timescales and processes across the entire Afar Rift System. The MAGMAFAR project will produce a significant number of deliverables that will gradually cover the description and understanding of magmatic OCT from individual processes to general models.

The discovery of the mass-independent isotopic fractionations of sulfur and oxygen (S-MIF and O-MIF) has revolutionized the way fundamental geochemical questions are addressed and have produced one of the most iconic figures in geosciences, i.e. the presence of S-MIF in rocks older than 2.3 billion years and its sudden quasi disappearance thereafter. Regarding O-MIF, the majority of the anomalies observed on Earth originate from the ozone anomaly transferred to oxygen-bearing molecules. Although there are still uncertainties pertaining to the mechanisms of O-MIF transfers, they tend to pale into insignificance when compared to those on the exact processes creating S-MIF. There is now no general consensus on the origin of S-MIF in the atmosphere and all the proposed mechanisms are still highly debated in geosciences. Recently NASA has identified the resolution of the origin of S-MIF as one of the top priorities for its astrobiology program, recognizing the importance of MIF in solving the epic question of the origin of life and its interaction with the planetary environment. The identification and quantitative understanding of processes involved in creating and transferring MIF anomalies, a prerequisite for extracting the information embedded in isotopic data, would certainly lead to major advances in our comprehension of the geochemical and environmental evolution of our Earth, from its most primitive existence to the present day. In this project, we propose a multidisciplinary approach to re-examine the sources of MIF in sulfates using an integrated program of novel laboratory experiments, dedicated field studies and innovative multi-scale atmospheric photochemical modeling (including both O- and S-MIF as prognostic variables). First, using the successful isotopic methodology applied to sulfate from polar snow and ice core, we will assess the potential of sulfate leached from volcanic ash as tracers of atmospheric oxidation processes. Second, we plan to carry out a new set of chamber experiments on SO2-related production of S-MIF considering environmental conditions that are as close as possible to those of the stratosphere and of the presupposed Archean atmosphere. Third, for the first time, S-MIF and O-MIF isotope chemistry schemes will be coupled and implemented in models (i.e. a photochemical box/plume model and a global chemistry-transport model). As O-MIF has already largely demonstrated its capacity to probe sulfur oxidation mechanisms in the atmosphere, combining O-MIF and S-MIF analysis should represent a powerful approach to constrain better inferences on the origin of S-MIF. One of the aims is to improve our quantitative understanding of oxidation processes of volcanic and anthropogenic sulfur, and of the resulting production of aerosols. We will also assess the potential of this innovative approach for probing atmospheric chemistry in the distant past. Overall, by providing a much more robust basis for quantitative inferences from S-MIF and O-MIF data, the project will yield new constraints on fundamental questions regarding the late oxygenation of the atmosphere, the shift from an anaerobic to aerobic environment for life, and the reconstruction of the impact of volcanic eruptions and human activities on atmospheric oxidizing capacity and climate.

Active fault zones are complex objects with physical properties and slip behavior constantly evolving in response to external mechanical constraints. In the brittle part of the crust, the deformation is rather localized, and the accumulated stresses are released by slip along the fault plane. Geodetic techniques, combined with seismology, have documented the spatial and temporal variability of slip modes at seismogenic depth (0-40 km). Slip rate on faults span a continuum ranging from mm/yr to m/s, and these seismic and aseismic conditions are not necessarily stable over time. Additionally, numerous studies have highlighted the strong coupling existing between the main fault plane and the surrounding medium. They suggest that on top of the “seismic cycle” there is a superimposed “cycle” where the properties of the fault zone evolve according to the sliding dynamics, which in turn influences the mode of deformation. However, the physics of the processes that controls these behaviors, and how it evolves in space and time, remains poorly understood. This severely limits our ability to assess the potential size, magnitude and recurrence of earthquakes on active faults. Therefore, to improve our understanding of active fault zones, seismic/aseismic slip and the evolving physical properties of the bulk must be studied as a unique system of stress accommodation and no longer as two distinct entities. However, to address this problem, the current numerical models of seismic cycle cannot be used. Deformation in the brittle crust is modeled by two planes, sliding one against the other and whose behavior is controlled by the properties of the interface only. Moreover, such models usually require to attribute constant properties (pressure, temperature, petrology, microstructure), that do not evolve with the deformation. Therefore, by ignoring the contribution of the evolving medium, the complex feedback, as described above, is not taken into account. It calls for a thorough research effort directed towards the development of a new generation of models that includes this entangled dynamic. With the help from the ANR program, we propose to study the evolution of the thermo-hydro-mechanical (THM) properties as a function of sliding and the counter-impact on the deformation mode. This project will provide a concerted view on fault behavior using a combined observational and theoretical approach. Developing new numerical tools, we will determine the first-order effect of the spatiotemporal variations of temperature, elastic properties and pore pressure by studying them separately. The theoretical development will be tested according to their ability to reproduce field data. For this part of the project, we will highly rely on previously published work and current projects the team-members are involved in (Taiwan, Philippines, Aegean region). Models will also help to identify the relevant parameters to document in the field or using geodesy, thus applying a true back-and-forth approach between numerical models and observations. This unique study will bring together knowledge from fracture mechanics, structural geology, laboratory experiments and geodetic analysis of active faults inside one project. It will add to our understanding of earthquake physics and aseismic deformation, therefore providing a much- needed mechanistic interpretation of fault slip behavior.

Earthquakes are the natural hazard with greatest impact on the world's populations, yet predicting when and where they will occur remains a key challenge. This is because earthquake triggering, and the consequent seismic and tsunami hazard potential, depends on the interplay of a range of regional and local factors that remain poorly constrained. This is particularly the case in broad zone of slow deformation of continental crust, such as along the African-Eurasian plate boundary (e.g. Alboran Sea; < 5 mm/a). In such intracontinental contexts of slow deformation, it is difficult to precisely constrain where elastic energy accumulates, when and how it is released and thus the resulting seismic hazard. The purpose of the ALBANEO project is to address key open questions regarding the functioning over time of an intra-continental fault system along an incipient plate boundary in the Alboran Sea, and its potential future evolution and implication for regional seismic and tsunami hazards. The project focuses on the Al Idrissi active Fault System in the Alboran Sea as a case study. The ALBANEO project proposes to use data from the 2021 ALBACORE oceanographic cruise (R/V Pourquoi Pas?, 2021) to obtain results on the distribution and style of deformation at and near the seafloor, on the mechanical and thermal properties of fault compartments, on their dynamic interactions with sedimentation, on seismic activity through time, and on past and present-day fluid flow through faults. The cruise targeted active fault segments hosted within Quaternary sedimentary systems including deep sea contourites and shelf sedimentary wedges. Specific questions to be addressed using data acquired during ALBACORE are: • What insights can be obtained from the sedimentary record about the tectonic control of depositional processes and seafloor morphology, slip rates and fault activity, and to build an accurate age model? • Over Quaternary timescales, where, when and how is the accumulated elastic energy released during earthquakes? • What are the physical properties of sediments and the dynamics and history of fluid flow of fault segments within the strike-slip system? Addressing these questions require a multidisciplinary and multi-scale approach. The ALBANEO project will use geophysical, geological, geotechnical, geochemical and geothermal data acquired during the ALBACORE oceanographic cruise. During ALBANEO, analyses of seismic profiles correlated to available sediment cores and in-situ data will allow us to construct the first accurate age model to evaluate slip rate and date co-seismic events that have affected the Alboran region during the last 130ka, as well as define a sequence stratigraphy model for the shelf wedge (Tasks #1 and #3). Geophysical, geochemical and geotechnical data will be used to constrain physico-chemical properties and fluid dynamics along the Al Idrissi Fault segments (Task #2). These analyses will provide inputs to kinematic and mechanical modelling of fault dynamics and strain partitioning (Task #4). Project results will be disseminated through a data management plan (Task #5). The results of ALBANEO will afford an improved understanding of earthquake triggering in a slow-slip and diffuse deformation setting. The study has strong societal interests for coastal communities and infrastructure as it will result in improved assessments of the risks related to earthquake, tsunamis and submarine landslide hazards.

The Alboran Sea is one of the most geologically active areas in the Mediterranean where submarine landslides with a tsunamigenic potential are present. The links between landslides, seismicity and tectonic movements are not obvious: the distribution of epicentres does not reflect the distribution of landslides; the mobilised material of target landslides is larger on gentle slopes. The stability of slopes seems to be controlled by interactions between several factors. The target area holds a variability in the distribution and type of slope instabilities. It therefore constitutes an appropriate key area to investigate how factors such as bottom current contourite deposition, fluid seepage and tectonic uplift precondition the stability of slopes and their link with seismic activity. The ALBAMAR project aims at understanding submarine landslides occurrence and frequency, to constrain the probability of future slope failures in the southern part of the Alboran Sea, for assessing landslide and tsunami hazard in this densely coastal populated region.