UC Davis

Back-arc spreading centers are unique tectonic environments where flux/hydrous melting at the arc occurs in close proximity to decompression melting observed at the back-arc. Numerical geodynamic models of back-arc spreading centers are constructed in order to describe the relationship between kinematically applied surface velocities and anhydrous melt formation, depletion, mantle flow, and slab dynamics. By tracking the evolution of the upwelling region, melt region, and depletion through time, we find that melt area and maximum melt fraction in back-arc spreading centers is primarily related to the back-arc spreading rate. Additionally, while having a smaller upwelling region than mid-ocean ridges with identical spreading rates, back-arc spreading centers have faster upwelling velocities due to flow geometry constrained by the adjacent sinking slab. Likewise, the geometry of the subducting slab is found to have a secondary effect on melt generation within the back-arc spreading center, with a nearly vertically sinking slab resulting in a ~1% increase in maximum melt fraction, especially early on in back-arc spreading. And finally, with the incorporation of two-phase flow, are able to generate oceanic crusts of thicknesses between 7 and 15 km within the back-arc using lower mantle potential temperatures than previous models and neglecting water. This suggests that incorporation of two-phase flow is essential for future models to accurately link melting, crust formation, fluid fluxes, and geochemistry.