Controls of Melt Genesis and Evolution at Buldir Volcano in the Western Aleutian Island Arc

The geochemistry of western Aleutian seafloor volcanoes indicates that primitive dacitic lavas (63-71% SiO2, Mg/Mg+Fe \u3e 0.65) containing low abundances of middle and heavy rare-earth elements (Yb) were probably produced by melting of an isotopically MORB-like (e.g., 87Sr/86Sr \u3c 0.7027) pyroxenite or subducted basaltic source. Andesites and dacites from emergent volcanoes throughout the Aleutians often also have low abundances of middle and heavy rare-earth elements (REE\u27s), but these characteristics are widely attributed to fractional crystallization and the removal of amphibole from mafic melts in crustal magma chambers. For this study, geochemical data were collected for 50 lavas from Buldir Volcano, the westernmost emergent volcano in the Aleutian island arc, to investigate the role of amphibole fractionation versus source variability in the genesis of andesites and dacites from Buldir. Buldir lavas range from basalt to dacite and define a strongly calc-alkaline or low-Fe igneous series. Andesites and dacites at Buldir have low abundances of middle and heavy REE\u27s