Bulk rock Pb, Hf, Nd and Sr isotopes and O18 isotopes from mafic rocks

The Famatinian arc, a Paleozoic subduction margin in northwestern Argentina, exhibits isotopic variations along its N-S axis (parallel to the paleo-subduction zone) that provide insights into crust formation and igneous processes at convergent margins. This study examines the isotopic compositions of intermediate to ultra-mafic rocks emplaced at different crustal levels to investigate the roles of mantle source contamination and crustal assimilation in generating the geochemistry of arc magmas. New bulk-rock Sr, Nd, Pb, and Hf isotope analyses of geochemically well-characterized mafic rocks, combined with in situ δ18O measurements in olivine and amphibole, demonstrate that sediment-derived contamination of the mantle source exerted a first-order control on the isotopic baseline of the primitive magmas. We find evidence that crustal assimilation has also contributed to the composition of the magmas emplaced at mid to upper crustal levels.