Foundering-driven lithospheric melting: The source of central Andean mafi c lavas on the Puna Plateau (22°S–27°S)


Investigations of lithospheric foundering and related magmatism have long focused on the central Andes, where there are postulated links between the eruption of mantle-derived lavas and periodic loss of the lower lithosphere. Whole-rock ele-mental and Nd-Sr-Pb isotopic results from a suite of late Miocene–Quaternary mafi c lavas erupted onto the Puna Plateau clarify the relationship between this hypothe-sized process and lava composition. Zinc and Fe provide a critical perspective because they are partitioned differently during the melting of asthenospheric and lithospheric mantle. All Puna lavas have Zn/FeT (×104) values>13, which requires clinopyroxene and perhaps garnet to be the dominant phase(s) in the melt source; this precludes a melt source of typical mantle asthenosphere. This result is contrary to classic models of delamination magmatism that suggest asthenospheric peridotite melts to gener-ate these lavas. Pyroxenite (±garnet)–bearing lithospheric materials in the central Andes are likely common and heterogeneous in age, volatile content, and mineralogi-cal composition, and if they are the melt source, this can explain the diversity in th

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