CE49 - Planétologie, structure et histoire de la terre

Magmatic Accretion and spreading ridge onset in Afar – MAGMAFAR

Submission summary

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.

Project coordinator

Monsieur Raphaël Pik (Centre de recherches pétrographiques et géochimiques)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

CRPG Centre de recherches pétrographiques et géochimiques
ISTEP Institut des sciences de la Terre Paris
CNRS DR12 - CEREGE Centre National de la Recherche Scientifique Délégation Provence et Corse - Centre européen de recherche et d'enseignement de géosciences de l'environnement
LSCE Laboratoire des Sciences du Climat et de l'Environnement
UBO-LGO Université de Bretagne Occidentale (UBO), Laboratoire Géosciences Océan (LGO)

Help of the ANR 570,458 euros
Beginning and duration of the scientific project: December 2020 - 48 Months

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