Schiano Pierre, David K., Vlastelic I., Gannoun A., Klein M., Nauret F., Bonnand P. (2012). Osmium isotope systematics of historical lavas from Piton de la Fournaise (Réunion Island, Indian Ocean). Contributions to Mineralogy and Petrology, 164 (5), p. 805-820. ISSN 0010-7999.
Titre du document
Osmium isotope systematics of historical lavas from Piton de la Fournaise (Réunion Island, Indian Ocean)
Schiano Pierre, David K., Vlastelic I., Gannoun A., Klein M., Nauret F., Bonnand P.
Source
Contributions to Mineralogy and Petrology, 2012,
164 (5), p. 805-820 ISSN 0010-7999
Re-Os isotope and elemental data have been obtained for 20 historical picrites and basalts (1931-2006) from the Piton de la Fournaise volcano on R,union Island and two old (> 0.78 Ma) cumulates from a drill hole in the eastern part of the volcano. The Os-187/Os-188 ratios of the historical lava samples, selected to cover the MgO concentration and Pb isotopic ranges of Piton de la Fournaise lavas, range from 0.1311 to 0.1374. This result, together with previous results on 66-Ma-old lavas from the Deccan Traps (AllSgre et al. in. Earth Planet Sci Lett, 170:197-204, 1999), supports the idea that the Os isotopic signature of the R,union plume is relatively uniform and is at the less radiogenic end of the ocean island basalt spectrum. In detail, lavas erupted before 1992 seem to have higher Os-187/Os-188 than the lavas erupted after the 1992-1998 period of quiescence. Comparison of Os-187/Os-188 ratios with Pb, Sr and Nd isotopic data on the same set of samples shows no correlation between Os and Sr-Nd isotopes, whereas a broad positive relationship with Pb isotopes is observed, which is interpreted to reflect coupled fractionation of Re/Os and U-Th/Pb in the mantle due to the partitioning of Pb and Os into sulphides. Lavas inferred to be recording the Os isotopic signature of the R,union plume source have higher Os-187/Os-188 ratios than the primitive mantle values. While this might be ascribed to melting of a lithologically heterogeneous source comprising recycled oceanic crust and/or continental sediment, the expected coupled Os-Sr-Nd-Pb isotopic variations are not observed. It is thus proposed that the mantle source for Piton de la Fournaise has inherently slightly radiogenic Os-187/Os-188 values that could reflect a mantle domain almost isolated from recycling processes.
