Fluid-mediated forearc mantle metasomatism and its chemical feedbacks: Insights from coupled petrological and thermomechanical modelling

Fluid-mediated mantle metasomatism (FMM) and associated matter transfer is a key process for subduction zone evolution. Over the past decade, the implementation of thermodynamic modelling into geodynamic numerical models became popular, boosting dozens of new insights into ongoing processes within mantle wedge.

Building on the work of Galvez et al. (2015) and Zhong and Galvez (2021), we now combine the original fluid speciation algorithm within a geodynamic model to obtain a chemo-thermo-mechanical modelling platform. It integrates a Gibbs free energy minimizer, e.g. Perple_X or MAGEMin (Connolly et al., 2005; Riel et al., 2022), the ‘single’ backcalculation algorithm (Backcalc, Galvez et al., 2015) with the thermo-mechanical code I2VIS (Gerya and Yuen, 2003) to investigate FMM. Specifically, the speciation and fractionation of electrolytic fluids are governed by cell-wise calculation from Backcalc, and fluid migration is computed assuming incompressible two-phase flow, whereby pore fluid pressure is assumed to be equal to the solid pressure (Faccenda et al., 2009). This new modelling platform is capable of capturing the chemical feedbacks on the geodynamic evolution of subduction zones. Our preliminary efforts have been to replicate the major elements fluxes from a kinematic model presented by Zhong and Galvez (2021) to test the successful combination of the codes. Our ‘benchmark’ tests show excellent agreement. Here, we will present some preliminary tests incorporating mechanical deformations of layers, and how such process, including mantle diapirism, may affect the trajectory of fluids and metasomatic pathways.