Volcanic-plutonic parity and the differentiation of the continental crust.

C Brenhin Keller,Jon M Husson,Blair Schoene,Melanie Barboni,Kyle M Samperton

doi:10.1038/nature14584

Abstract

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.

Highlights

Introduction this comparison provides insight into the predominant mechanisms of igneous differentiation and the origins of crustal
Earth is the only planet in our solar system with a highsilica continental crust, which is complemented by a low-silica stratification, and since magmas that reach the Earths surface are more efficiently recycled back into the mantle via erooceanic crust similar to that of the Moon, Mars and Venus [1, 2]. sion and subduction into crust-mantle geochemical evolution
Detailed investigations of specific igneous systems have revealed that mantle-derived basaltic melts differentiate to higher silica contents through processes such as fractional crystallization, metamorphism, and remelting of crustal material

Summary

MELTS simulations

We have approached the problem through a brute-force Monte Carlo approach, minimizing 1.36 million MELTS fractionation paths with differing starting compositions and P-T paths to fit the observed crustal differentiation trends. These simulations were conducted using the alphaMELTS [53] v1.4.1 command-line version of the MELTS and pMELTS thermodynamic modelling software [52] along with parallel scripting codes. The MELTS results do unequivocally demonstrate that fractionation of the the calculated cumulate compositions can accurately reproduce the observed average major element differentiation trends

Trace element calculations

Solidus temperature of hydrous and dry magmas

Causality of the plutonic water correlation

Findings

Eu anomalies