Interaction Between Mantle-Derived Magma and Lower Arc Crust: Quantitative Reactive Melt Flow Modelling Using STyx

The magmatic processes occurring in the lowermost arc crust plays a major role in the evolution of mantle wedge derived melt. Geological evidence indicate that mantle-derived magmas and in situ products of lower crust partial melting are reacting in a pervasive melt system, and are eventually extracted toward higher level of the crust. Resolving the relative contribution of mantle-derived magma and partial melting products of pre-existing crust is essential to: (1) quantify crustal growth rate, (2) better understand the compositional range of arc magmatic series and (3) constrain the chemical differentiation of the lower crust. In this study, we present STyx, a new modeling tool, coupling melt and heat flow with petrology to explore the dynamics of storage, transfer and hybridization of melts in complex liquid/rock systems. We perform three models representing a magmatic event affecting an amphibolitic lower arc crust in order to quantify the relative contribution between partial melting of the pre-existing crust and fractional crystallization from mantle-derived hydrous-magma. Our models demonstrate that most of the differentiated arc crust is juvenile, deriving from the differentiation of mantle melts, and that pre-existing crust does not significantly contribute to the total volume of magmatic products.