Solubility of Os and Ir in sulfide melt: Implications for Re/Os fractionation during mantle melting

Autor(es)

Fonseca, Raul O. C. ^[1] ; Mallmann, Guilherme ^{[2, 3]} ; O'Neill, Hugh St C. ^[3] ; Campbell, Ian H. ^[3] ; Laurenz, Vera

Afiliação do(s) autor(es)

^[1] Univ Bonn, Steinmann Inst, Poppelsdorfer Schloss Museum, D-53115 Bonn - Germany

^[2] Univ Sao Paulo, Inst Geociencias, BR-05508080 Sao Paulo - Brazil

^[3] Australian Natl Univ, Res Sch Earth Sci, Canberra, ACT 0200 - Australia

• Tipo de documento: Artigo Científico
• Fonte: Earth and Planetary Science Letters; v. 311, n. 3-4, p. 339-350, NOV 15 2011.
• Citações Web of Science: 46

Resumo

Although both rhenium (Re) and osmium (Os) are highly siderophile elements (HSE), they show contrasting geochemical behaviors during partial melting of the mantle - Re is mildly incompatible whereas Os appears to be compatible. This fundamental difference, unique among commonly used isotopic chronometers, causes large variations of Re/Os in oceanic basalts. However, which mantle phases control the geochemical behavior of these elements during partial melting is controversial. Sulfide is typically regarded as a major host for these elements, but recent studies have shown that silicate phases and spinel may also play a role. Here we report the results of an experimental study on the solubilities of Os and Ir in sulfide melts (or mattes) over a large range of oxygen (fO(2)) and sulfur (fS(2)) fugacities at 1300 degrees C. Our experiments indicate that the solubilities of Os and It in mattes increase with increasing fS(2). with both Os and Ir dissolving as trivalent species at high fS(2) and metallic species at low fS(2). The effect of fO(2) on Os and It solubilities appears to be related to oxygen being dissolved into the matte at more oxidizing conditions. Our results coupled with solubility data for Os and Ir in silicate melts have enabled matte/silicate melt partition coefficients for these elements (D(i)(matte/sil)) to be calculated. Assuming a relative oxygen fugacity equal to the quartz-fayalite-magnetite redox equilibrium (i.e. QFM) and a sulfur fugacity of 10(-0.5) bar, calculated D(Os)(matte/sil) is similar to 10(4) and D(lr)(matte/sil) is similar to 10(6). The low solubilities of Os and It in silicate melts, coupled with their high matte/silicate melt partition coefficients, suggest that Os and It in fertile mantle with similar to 200 ppm S are held in the mantle matte phase. However, we show that the empirical range of Re/Os in mid-ocean ridge basalts (MORB) can only be reproduced when sulfide is exhausted by high degrees of partial melting, leaving Os-It-rich metal alloy in the mantle residue. (C) 2011 Elsevier B.V. All rights reserved. (AU)

• Processo FAPESP: 10/05512-1 - Estudos experimentais de acresção e diferenciação planetária
• Beneficiário: Guilherme Mallmann
• Modalidade de apoio: Auxílio à Pesquisa - Jovens Pesquisadores