How reactive porous flow shapes magmatic systems : A thermodynamic approach

The physical and chemical evolution of magmatic systems is strongly influenced by ubiquitous reactive porous flow (RPF) during the mushy state, which has been proposed to explain the textural and chemical signatures observed in plutonic rocks. Melt–mush reactions play a key role in governing the evolution of systems containing both cumulate-forming minerals and percolating interstitial melts. In oceanic settings, RPF has been extensively investigated using volcanic and plutonic records, demonstrating its strong influence on oceanic crust, including MORB, compositions. However, most of the existing studies are qualitative, and lack strong thermodynamic constraints on the feasibility and parameters of the reactions.

Here, we used forward thermodynamic modeling with the Perple_X program to constrain the modal and chemical compositions of the phases involved in melt–mush reactions, as well as the physicochemical conditions associated with RPF signatures in plutonic rocks from oceanic ridges. Constraints on RPF-induced reactions are obtained through a parametric study that explores variations in reactive melt composition, percolated mush composition and temperature. Our results define the range of thermodynamically viable reactions and reaction products, showing that melt–mush reactions can partially reproduce the typical signatures observed in plutonic rocks (e.g., Mg#–Ti in clinopyroxene). These reactions also generate significant modal variations, primarily controlled by mush chemistry and temperature. Considering the entire mushy plumbing system, from the mushy reservoirs to seafloor-emplaced lavas, we demonstrate that reactive porous flow explains the compositions of both oceanic plutonic rocks and MORB melts. Although we herein focus on reactions occurring in oceanic magmatic reservoirs, the developed approach can be applied to any type of mush-dominated magmatic system.