One View of the Geochemistry of Subduction-Related Magmatic Arcs, with an Emphasis on Primitive Andesite and Lower Crust

This chapter has four main aims. Provide a comprehensive picture of the composition of volcanic rocks from subduction-related magmatic arcs. Review evidence in favor of the existence of andesitic, as well as basaltic primary magmas in arcs. Present new data on the composition of arc lower crust, based mainly on our work on the Talkeetna arc section in southcentral Alaska. Summarize evidence from arc lower crustal sections that a substantial proportion of the dense, lower crustal pyroxenites and garnet granulites produced by crystal fractionation are missing.