@article {TURNER2015182,
	title = {The global chemical systematics of arc front stratovolcanoes: Evaluating the role of crustal processes},
	journal = {Earth and Planetary Science Letters},
	volume = {422},
	year = {2015},
	pages = {182 - 193},
	abstract = {Petrogenetic models for convergent margins should be consistent with the global systematics of convergent margin volcanic compositions. A newly developed tool for compiling and screening data from the GEOROC database was used to generate a global dataset of whole rock chemical analyses from arc front stratovolcano samples. Data from 227 volcanoes within 31 volcanic arc segments were first averaged by volcano and then by arc to explore global systematics. Three different methods of data normalization produce consistent results that persist across a wide range of Mg$\#$ [Mg$\#$=Mg/(Mg+Fe)]. Remarkably coherent systematics are present among major and trace element concentrations and ratios, with the exception of three arcs influenced by mantle plumes and Peru/N. Chile, which is built on exceptionally thick crust. Chemical parameters also correlate with the thickness of the overlying arc crust. In addition to previously established correlations of Na6.0 with Ca6.0 and crustal thickness, correlations are observed among major elements, trace elements, and trace element ratios (e.g. La/Yb, Dy/Yb, Zr/Sm, Zr/Ti). Positive correlations include {\textquotedblleft}fluid mobile,{\textquotedblright} {\textquotedblleft}high field strength,{\textquotedblright} and {\textquotedblleft}large ion lithophile{\textquotedblright} element groups, with concentrations that vary by a factor of five in all groups. Incompatible element enrichments also correlate well with crustal thickness, with the greatest enrichment found at arcs with the thickest crust. Intra-crustal processes, however, do not reproduce the global variations. High pressure fractionation produces intermediate magmas enriched in aluminum, but such magmas are rare. Furthermore, differences among magma compositions at various volcanic arcs persist from primitive to evolved compositions, which is inconsistent with the possibility that global variations are produced by crystal fractionation at any pressure. Linear relationships among elements appear to be consistent with mixing between depleted primary magma and an enriched contaminant, but the required composition of the theoretical enriched end-member is not similar to compositions expected in the deep crust or to any known rock composition. The large-scale chemical variations among volcanic arcs are therefore likely to be generated by processes in the subducting slab or mantle wedge, rather than the crust. While crustal processes are important in the differentiation of convergent margin magmas, they do not account for the systematics presented here. Models that attribute the chemical variability of arc magmas to slab or wedge processes are also constrained to be consistent with the global chemical systematics, and are discussed in Turner and Langmuir (2015).},
	keywords = {arc, chemistry, Global, petrology, subduction, volcano},
	issn = {0012-821X},
	doi = {https://doi.org/10.1016/j.epsl.2015.03.056},
	url = {http://www.sciencedirect.com/science/article/pii/S0012821X15002228},
	author = {Stephen J. Turner and Charles H. Langmuir}
}
