Petrology and geochemistry of the Galapagos Islands: portrait of a pathological mantle plume

Abstract

Reports new major element, trace element, isotope ratio, and geochronological data on the Galapagos Archipelago. Magmas erupted from the large western volcanoes are generally moderately fractionated tholeiites of uniform composition; those erupted on other islands are compositionally diverse, ranging from tholeiites to picritic basanitoids. Isotope and incompatible element ratios define a horseshoe pattern with the most depleted signatures in the center of the Galapagos Archipelago and the more enriched signatures on the eastern, northern, and southern periphery. These isotope and incompatible element patterns appear to reflect thermal entrainment of asthenosphere by the Galapagos plume as it experiences velocity shear in the uppermost asthenosphere. Both north-south heterogeneity within the plume itself and regional variations in degree and depth of melting also affect magma compositions. -from Authors