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Geochemical systematics of Pb isotopes, fluorine, and sulfur in melt inclusions from São Miguel, Azores

Abstract : Pb isotopic measurements in olivine-hosted melt inclusions of ocean island basalts (OIBs) from São Miguel, Azores, reflect the high 207 Pb/ 204 Pb and 208 Pb/ 204 Pb at a given 206 Pb/ 204 Pb of their host lavas. The data are consistent with a mixture between two endmembers: the first (the Central Group) has relatively high 208 Pb/ 206 Pb and is similar to the component sampled by Graciosa and Faial, and the second is a radiogenic endmember (with low 208 Pb/ 206 Pb) that we refer to as the Nordeste component. F and Cl concentrations measured in the same melt inclusions from São Miguel represent parental abundances unmodified by crustal assimilation. Based on undegassed F and Cl concentrations, the source beneath São Miguel is volatile-rich. Among melt inclusions, Pb-isotope compositions correlate positively with S concentrations: we attribute this correlation to the dissolution of oceanic crust sulfides in the S-undersaturated basaltic melt of the Nordeste component. The blebs were assimilated by São Miguel magma and the magma droplets were later trapped in olivines. When comparing melt inclusions from worldwide OIBs representing mantle endmembers, we find a global negative correlation between F/Nd and 208 Pb/ 206 Pb of volcanic glasses and melt inclusions. The high F/Nd (up to 40) endmember is represented by HIMU melt inclusions and the low F/Nd (down to 14) by EM1 Pitcairn glasses. São Miguel melt inclusions have an intermediate F/Nd = 23.1±3.4.
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Estelle Rose-Koga, K.T. Koga, M. Moreira, Ivan Vlastélic, M.G. Jackson, et al.. Geochemical systematics of Pb isotopes, fluorine, and sulfur in melt inclusions from São Miguel, Azores. Chemical Geology, Elsevier, 2017, 458, pp.22 - 37. ⟨10.1016/j.chemgeo.2017.03.024⟩. ⟨hal-01636195⟩



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