Volcanic-Plutonic Parity and the Differentiation of the Continental Crust

Brenhin Keller, Princeton University

Photo of Brenhin Keller

The continental crust is central to the biological and geological history of Earth. However, crustal heterogeneity has prevented a thorough geochemical comparison of its primary igneous building blocks – volcanic and plutonic rocks – and the processes by which they differentiate to felsic compositions. Our analysis of a comprehensive global dataset of volcanic and plutonic whole-rock geochemistry shows that differentiation trends from primitive basaltic to felsic compositions are statistically identical for volcanic and plutonic samples in subduction zone settings, but divergent in continental rifts. Offsets in major- and trace-element differentiation patterns in rift settings implicate higher water content in plutonic magmas and reduced eruptibility of hydrous silicate magmas. In both tectonic settings, our results indicate that fractional crystallization, rather than crustal melting, is responsible for the production of intermediate and felsic magmas, emphasizing the importance of mafic cumulates for the evolution of the continental crust.

Abstract Author(s): Brenhin Keller, Blair Schoene