Geochemical comparison between oceanic and continental arc volcanic rocks: Insights to arc magmatism

Compositional differences between continental and oceanic arc volcanic rocks have long been recognized; however, our understanding of them is incomplete. This study presents a comprehensive geochemical comparison, including major, trace and Sr-Nd-Pb isotope compositions, between global continental and oceanic arc volcanic rocks. Our data compilation reveals that volcanic rocks from a single oceanic arc occupy basaltic to basaltic-andesitic average lithochemical compositions, except for volcanic rocks from the Lesser Antilles arc, which occupies an andesitic average lithochemical composition, similar to the bulk composition of volcanic rocks from single continental arcs. The composition of the average continental arc volcanic rocks, the average Lesser Antilles arc volcanic rocks and the average oceanic arc volcanic rocks are different in many ways, which span the entire compositional range from basalts to rhyolites, and are reflected in major, trace element and Sr-Nd-Pb isotope compositions. Qualitative geochemical analyses and semi-quantitative modelling suggest that the compositional differences in mafic arc volcanic rocks can be accounted for by differences in source mixing between mantle wedge peridotite and slab-derived crustal components. Slab melts-peridotite source mixing governs most of the lithochemical features of the continental arc and the Lesser Antilles arc mafic volcanic rocks, which is especially true for Sr-Nd-Pb isotopes. On the other hand, such source mixing occurred to a lesser extent in the petrogenesis of oceanic arc mafic volcanic rocks. Magma evolution processes such as fractional crystallization may further modify the lithochemical composition of the arc volcanic rocks, especially the felsic ones, but this is not the governing factor.