Central Andean magmatism can be constrained by three ubiquitous end-members

The geochemical character of primary magmas and the nature of crustal melts remain poorly constrained at the active continental margin of the Central Andes, where the crustal thickness is >70km. We identify three end-members and constrain their full major and trace element compositions by polytopic vector analysis (PVA). The end-members include two mafic parent magmas: (1) a slightly evolved calcalkaline basaltic andesite derived from the fluid-fluxed mantle wedge that is typical of the Andes in general and (2) a strongly LREE-enriched basalt akin in its trace element pattern to back-arc shoshonites. (3) The third end-member is a variably HREE-depleted rhyodacite representing partial melts of lower to middle crustal lithologies. We propose that these end-members are ubiquitous and typical of such thick-crust settings, and can explain - in highly variable mixing proportions - the entire compositional range of Central Andean magmatism.