Over the last decades, magma reservoir models gradually shifted from melt- to mush-dominated environments, in particular at mid-ocean ridges where geophysical surveys describe limited melt fractions at depth. Together with the identification of disequilibrium textures and anomalous geochemical signatures in minerals from oceanic gabbros, evidence for the presence of a mush at depth prompts us to reconsider the relative importance of (fractional) crystallization and melt-mush reactions (MMR) in differentiation processes. So far, most of our understanding of melt-mush reactions relies on natural samples that record a series of events until complete solidification of the rock. Numerical models (geochemical, thermodynamic) can be used to constrain evolution trends after disturbance of the initial state of equilibrium of the mush, yet the coupled effect of composition and temperature (“chemical melting” vs “thermal melting”, Hu et al., 2022, Journal of Petrology, 63, 1-28) is rarely considered. Only few experimental studies tried to reproduce “instantaneous” melt-mush reactions, and several questions remain regarding the efficiency of melt-mush reactions and their quantification.
Here, we present the first results of disequilibrium experiments conducted in a piston-cylinder at 0.3 GPa and 1100-1200°C. We carried out a series of experiments reproducing the interaction of a fine-grained gabbro with “reactive” MORB melts. The initial gabbros were all sampled from IODP U1473A and ODP 735B drilled cores from the Atlantis Bank oceanic core complex and were previously characterized in detail for their texture, microstructure, and mineral compositions. The experimental run products were analyzed by X-ray computed tomography and high-resolution FEG-SEM to track small-scale textural and compositional changes from the starting solid material and the location of melt. The first results help us constrain the stoichiometry of MMR and inform us about the local changes in texture during the reactions.