Abstract

The compositional variability of convergent margin stratovolcanoes can be assessed on multiple scales: within a single edifice, a single arc, or among arc averages. Quantitative models of subduction processes are constrained by the relationships between magma chemistry and subduction parameters pertinent to the down-going plate (age, dip angle, sediment thickness and composition), the overriding plate (Moho depth), or both (convergence rate). The subduction parameters are inter-related, however, so caution must be exercised when positing causal relationships between physical and chemical observations. Arc-averaged magma compositions correlate globally with down-going plate parameters, Moho depth, and possibly the p-wave velocities beneath the arc front, and each of these observations motivate very different models of compositional variability. Natural regional experiments can be used to test the validity of models developed on the basis of global correlations. The Chilean southern volcanic zone (SVZ) serves as a laboratory to isolate the effects of the overriding vs down-going plate. I will present a synthesis of new and existing data from the SVZ and show how these data constrain global and local models of convergent margin volcanism, demonstrating the importance of the upper plate in regulating melt generation. Numerical simulations provide additional physical justification for this model.

Turner, S. J., & Langmuir, C. H. (2015). The global chemical systematics of arc front stratovolcanoes: Evaluating the role of crustal processes. Earth and Planetary Science Letters, 422, 182-193.

Turner, S. J., & Langmuir, C. H. (2015). What processes control the chemical compositions of arc front stratovolcanoes?. Geochemistry, Geophysics, Geosystems.