Socorro and San Benedicto Islands in the Eastern Pacific Ocean are remarkable because they are located on the axis of a recently abandoned spreading center (-3.15 Ma ago) and yet are still volcanically active. Moreover, Socorro Island is unique in being the only predominantly salic peralkaline oceanic island in the Pacific Ocean. This research will document the geologic and geochemical histories of Socorro and San Benedicto Islands in the context of ridge failure. Major and trace element, 40Ar-39Ar geochronology, and Sr, Nd, Pb, and Th isotopic analyses of whole rocks, glasses and phenocrysts will be conducted on samples from submarine topographic highs in the region. The purpose of the research is to: 1) characterize the geochemical evolution of Socorro and San Benedicto Islands; 2) constrain the depth and possibly volume of the magma reservoir beneath Socorro; 3) document the relative importance of compositional stratifications versus mafic recharge in explaining both the eruptive history of Socorro Island and the origin of salic peralkaline magmas; and 4) 4) establish the temporal and geochemical relationship between sources of recent regional magmatism and those of the abandoned mid-ocean spreading center.
