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Abstract:
Estimates of volumetric magmatic flux vary significantly between arc volcanoes, both globally and between volcanoes in a given arc. A recent case study of the Cascades arc suggested that variation in basaltic flux from the mantle causes heterogeneity in surface volcanic flux. The root causes of such variations are poorly known, and could relate to along-arc variations in fluid flux from the subducting oceanic lithosphere, changes in mantle thermal structure or composition, or subduction geometry. We model the volumetric flux of magma from the mantle using a simplified 3-D box model of a subduction zone to constrain the physical factors that most influence the volume of magma produced in the mantle over time. We evaluate the relative contributions of the extents and styles of melting at subduction zones and of the physical parameters of subduction to volumetric flux in a Monte Carlo calculation. Our results suggest that the volume of mantle available to melt, the extent of wet (flux) melting, and convergence rate are the most important factors controlling volumetric flux. In cases where calculated volumetric flux closely approximates published estimates of volcanic flux, we predict that melting is not constrained to the mantle directly below volcanic edifices, suggesting that magma supplied to the lithosphere requires lateral transport to “feed” the central edifices of volcanoes.Results from our model may aid in the interpretation of geochemical features like similarity of primitive magmas at adjacent volcanoes and support the idea that mantle magma supply may be an important control on volcano spacing.
