He-Ne-Ar Isotope Studies in Iceland, Heard Island and La Palma (Canaries): Identifying Mantle Plume Signatures and Crustal Contamination

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9614347 Hilton The presence of distinct reservoirs in the mantle as indicated by the geochemical and isotopic characteristics of ocean island basalts provide key constraints on the geodynamic history of the earth. This proposal seeks to characterize the He-Ne-Ar isotopic compositions and concentrations of samples from three ocean islands previously studied for their geochemical and Sr-Nd-Pb isotope systematics that show different mantle affinities: Heard Island (EM1/EM2), Iceland (DMM-FOZO), and La Palma, Canaries (HIMU). The proposed work will search for rare gas differences between the different mantle source reservoirs and will consider the degree of coupling between rare gases and radiogenic isotopes. A specific aim will be to test the presence of a mantle component (FOZO or 'C') common to all three ocean islands. If present, an attempt will be made to characterize its rare gas and radiogenic isotope systematics. An important aspect of this work will be to compare the results obtained by measuring different sampling media (i.e. geothermal fluids, glass rims of basalts, and mafic phenocrysts) to evaluate their capabilities for preservation of features that are characteristic of the mantle source region or susceptibility to modification by upper-crustal (magma chamber) processes. Another goal of this study will be to consider the integrity of the 'low-3He' hotspot signal found in some ocean islands to evaluate if this is a mantle feature or a crustal overprint introduced immediately prior to eruption in crustal magma chambers.