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Reactive porous or focused melt flows are common in crystal mushes of mid-ocean ridge magma reservoirs. Although they exert significant control on mid-ocean ridge magmatic differentiation, their role in metal transport between the mantle and the ocean floor remains poorly constrained. Here we aim to improve such knowledge for oceanic crust formed a...
Volcanism is the surface expression of extensive magmatic systems, with their intrusive counterpart representing~80% of the total magma budget. Our knowledge of igneous processes therefore largely relies on our understanding of deep plutonic processes. In continental or oceanic environments, most of the intrusive igneous rocks bear geochemical cumu...
Excel spreadsheet for prediction of rare earth element partitioning between clinopyroxene and alkaline melts
Magmatic processes that govern crustal accretion at mid-ocean ridges still need to be better constrained. Among the processes potentially involved in the evolution of the lower crust magma reservoirs, reactions associated with reactive porous flow through crystal mushes tend to be considered as one of the predominant processes together with simple...
Oceanic crust accreted at mid-ocean ridges represents ~70% of Earth's surface; nevertheless magmatic processes implicated in the formation of the lower crust remain poorly understood. Fossilized sections document its complexity in structure and composition, and recent studies show that melt migration and interactions within a crystallizing mush are...
Layered portions of gabbros were described at slow-spreading environments in at least two different Oceanic Core Complexes (OCC), which are interpreted as exhumed portions of lower crust at the ridge axis. Two ODP-IODP Holes drilled into the Atlantis Bank OCC (SW Indian Ridge) present locally such features, which provide essential insights on melts...
Magma evolution in the lower oceanic crust affects the metal contents in the derivative magmas and the formation of seafloor massive sulfides. At spreading segments with low magma supply, sulfide differentiate primarily by melt-mantle reaction, with subordinate role of fractional crystallization 1,2. At spreading segments with high magma supply, di...
The main objective is to have a better understanding of the geodynamic evolution of continental rifts by providing new constraints on the igneous processes taking place in such areas. The respective roles of mantle source modal and chemical compositions, of the parental melt composition, of the plumbing system architecture, of the magma chamber(s) processes like melt-rock reactions, fractional and in-situ crystallization, fresh-melt recharge and related mixing, and crustal contamination will be characterized and quantified. This will allow us to bring new constraints on the spatial and temporal variability of igneous processes in a given rift segment, and more generally along continental rifts. The interplay between tectonic evolution and magmatism is also examined in details. In order to make striking and representative advances with this project, various continental rifts are considered: *French Massif Central *Afar region *Tanzanian section of the East-African Rift
GECO-REE will identify and quantify the magmatic processes responsible for the genesis of the principal Rare Earth Element (REE) deposits on Earth (carbonatite igneous rocks) through an integrated study (from mantle source to the final REE-enriched product) of the only active carbonatitic volcano on Earth. This unique system represents a natural laboratory for carbonatite genesis as it provides samples documenting the successive steps of the REE concentration process, from the mantle source, through the plumbing system that acts as an enriching filter, to the final REE-enriched product. We will characterize the protracted differentiation of mantle melts to carbonatites, the evolution of the REE contents of those melts, and the composition of the successive associated cumulative mineral assemblages (the intrusive component), which correspond to REE-bearing minerals in currently mined deposits. The composition, temperature, pressure, and redox conditions required for the onset of carbonatite immiscibility during differentiation will be quantified for the first time. The partition coefficients that govern each step of the REE concentration process (=differentiation), and their dependence on temperature, composition, and volatile content will be quantified for both mineral-liquid and carbonatitic melt-silicate melt partitioning. GECO-REE is multidisciplinary, and will take advantage of the expertise of the young researcher consortium in igneous and raw material petrology, and trace element and isotopic geochemistry. GECO-REE will provide the first integrated metallogenic model for the genesis of REE deposits, and will represent a real industrial capital gain for exploration companies. GECO-REE is funded by French National Research Agency (ANR-16-CE01-0003-01), and is supported by the LabEx RESSOURCES21 (ANR-10-LABX-21-01).