Volcanic–plutonic parity and the differentiation of the continental crust

• Published in: Nature (London) 2015-07, Vol.523 (7560), p.301-307
• Main Authors: Keller, C. Brenhin, Schoene, Blair, Barboni, Melanie, Samperton, Kyle M., Husson, Jon M.
• Format: Article
• Language: English
• Subjects: 704/2151/209; 704/2151/213; 704/2151/431; 704/2151/598; Analysis; Continental crust; Crystallization; Datasets; Earth; Geochemistry; Geological history; Heterogeneity; Humanities and Social Sciences; Igneous rocks; Magma; Methods; multidisciplinary; Rocks; Science; Silicates; Stratigraphy; Tectonics; Trace elements; Trends; Water content
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature14584

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 data set of volcanic and plutonic whole-rock geochemistry shows that differentiation trends from primitive basaltic to felsic compositions for volcanic versus plutonic samples are generally indistinguishable in subduction-zone settings, but are divergent in continental rifts. Offsets in major- and trace-element differentiation patterns in rift settings suggest higher water content in plutonic magmas and reduced eruptibility of hydrous silicate magmas relative to dry rift volcanics. In both tectonic settings, our results indicate that fractional crystallization, rather than crustal melting, is predominantly responsible for the production of intermediate and felsic magmas, emphasizing the role of mafic cumulates as a residue of crustal differentiation. A global geochemical data set of volcanic and plutonic rocks indicates that differentiation trends from primitive basaltic to felsic compositions for volcanic versus plutonic samples are generally indistinguishable in subduction-zone settings, but are divergent in continental rifts. Continental crust formation Brenhin Keller and co-authors present a global geochemical dataset of the two fundamental building blocks of the continental crust, volcanic (externally erupted) and plutonic (internally solidified) rocks. Their results indicate that differentiation trends from primitive basaltic to felsic compositions for volcanic versus plutonic samples are generally indistinguishable in subduction-zone settings, but divergent in continental rifts. Offsets in major- and trace-element differentiation patterns in rift settings suggest higher water content in plutonic magmas and reduced eruptibility of hydrous silicate magmas relative to dry rift volcanics. This work indicates that in both tectonic settings, fractional crystallization rather than crustal melting is predominantly responsible for the production of intermediate and felsic magmas.