MAGMA PRODUCTION BENEATH SUBDUCTION ZONES: USING NUMERICAL MODELS TO EVALUATE MELT PRODUCTION

Melt production at subduction zones depends on mineral composition, water content, age of the plate, dip angle of the plate subducting, rate of convergence, age of the slab, and length of the forearc. It has proven challenging to understand how melting changes when any single factor, or combination of these factors, changes. This project examines differences in subduction melting resulting from the changes of several different variables. These variables include initial modal clinopyroxene (cpx), and its exhaustion, mantle hydration, dip angle, rate of convergence, plate and slab age, and forearc cold corner depth. To do this, we constructed 2D numerical models of temperature, mantle flow, and melt production at subduction zones. We ran a variety of models that tracked changes in the total melt as the combination of parameters was altered in each trial. The dip angle of the subducting slab is varied from 30 to 75 degrees, rate of the slab between 20 and 90 km/Myr, age of the plate between 20 and 90 Myr, forearc depth between 40-50 km, and hydration set at 0.1%, 0.5%, and 0.01 wt%. The slab age and initial modal cpx levels are held constant throughout all the trials at 60 Myr and 15%, respectively. Each of these parameters affect the overall melt production, with melting seeming to peak for models set with hydration content at 0.1%, the dip angle at 60 degrees, the highest convergence rates, and the youngest ages. Changes in forearc length, in addition to each combination of the other parameters, also effect amount of overall total melt with longer forearcs resulting in less melt than shorter forearcs.