Melt inclusions in Iceland olivines as tracers of primary mantle melt compositions

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The aim of this project is to investigate the source chemistry of the Iceland plume by insitu analysis (major and trace elements and isotopes) of primary melts represented by glassy inclusions in early-formed phenocrysts from Iceland picrites and olivine tholeiites. We have previously shown that in Hawaiian tholeiites, extreme chemical and isotopic heterogeneities seen in melt inclusions reflect true source heterogeneities, in addition to displaying the effects of progressive fractional melting. By studying the Iceland plume, where melting is at a much shallower level than beneath Hawaii, we hope obtain a clearer picture of the variations of source chemistry of a plume. Apparently, Iceland resembles Hawaii in that both plumes contain recycled ocean crust, and specific components of this former crust, such as gabbros, can be recognized by their geochemical fingerprints. In addition, we expect to gain a better understanding of mechanisms of melt extraction and of possible chemical zoning of the Iceland plume. Seismic tomography indicates that the diameter of the Iceland plume (100 km) is significantly smaller that of the island (250 km). This should enable us to map out the source chemistry and relate it to the tomographic "image" of the plume.