TY - JOUR
T1 - An experimental study of the solubility and partitioning of iridium, osmium and gold between olivine and silicate melt
AU - Brenan, James M.
AU - McDonough, William F.
AU - Ash, Richard
N1 - Funding Information:
We are grateful to Kevin Righter, Wim van Westrenen and an anonymous reviewer for their comments on the manuscript. Funding for this research was provided by grants to JMB from the Natural Sciences and Engineering Research Council of Canada and to WFM from the U.S. National Science Foundation and NASA.
PY - 2005/9/15
Y1 - 2005/9/15
N2 - We have performed metal solubility and olivine-melt partitioning experiments to understand the behaviour of iridium, osmium and gold during crust-mantle differentiation. All experiments were performed metal-saturated, with molten gold added to suppress nugget formation. Coexisting olivine and iron-bearing basalt glass produced in experiments at 1 bar (105 Pa), 1260-1350 °C and fO2 of FMQ + 0.6 to + 5.4 were analysed by laser ablation ICPMS. Olivine-melt partition coefficients (Ds) for Ir increase from ∼0.4 at FMQ + 5.4 to ∼2 at FMQ + 2.5, with the latter value being consistent with the behaviour of Ir in lavas that have evolved by olivine fractionation. The increase in DIr with decreasing fO2 is consistent with an increase in the relative proportion of Ir2+ in the melt, as it has an estimated ionic radius close to the "strain-free" value for octahedral coordination in olivine. Gold is highly incompatible in olivine (D = 1 - 2 × 10-3 or less), consistent with its relatively large ionic radius in the Au1+ oxidation state. This, together with our previous measurements of olivine-melt partitioning for Pt, Pd, Ru and Rh, indicates that olivine-equilibrated melts will have depletions in Ir, Rh and Ru relative to Pt, Pd and Au, consistent with that measured in primitive, sulfur-poor magmas. Our data provide an upper bound on Os solubility in silicate melt of 10 ppb at FMQ + 0.6, even though Os partition coefficients could not be measured. The solubility of Os, Ru and Ir in silicate melt is comparable to the concentrations of these elements in primitive, sulfur-poor magmas, suggesting they could be metal-saturated.
AB - We have performed metal solubility and olivine-melt partitioning experiments to understand the behaviour of iridium, osmium and gold during crust-mantle differentiation. All experiments were performed metal-saturated, with molten gold added to suppress nugget formation. Coexisting olivine and iron-bearing basalt glass produced in experiments at 1 bar (105 Pa), 1260-1350 °C and fO2 of FMQ + 0.6 to + 5.4 were analysed by laser ablation ICPMS. Olivine-melt partition coefficients (Ds) for Ir increase from ∼0.4 at FMQ + 5.4 to ∼2 at FMQ + 2.5, with the latter value being consistent with the behaviour of Ir in lavas that have evolved by olivine fractionation. The increase in DIr with decreasing fO2 is consistent with an increase in the relative proportion of Ir2+ in the melt, as it has an estimated ionic radius close to the "strain-free" value for octahedral coordination in olivine. Gold is highly incompatible in olivine (D = 1 - 2 × 10-3 or less), consistent with its relatively large ionic radius in the Au1+ oxidation state. This, together with our previous measurements of olivine-melt partitioning for Pt, Pd, Ru and Rh, indicates that olivine-equilibrated melts will have depletions in Ir, Rh and Ru relative to Pt, Pd and Au, consistent with that measured in primitive, sulfur-poor magmas. Our data provide an upper bound on Os solubility in silicate melt of 10 ppb at FMQ + 0.6, even though Os partition coefficients could not be measured. The solubility of Os, Ru and Ir in silicate melt is comparable to the concentrations of these elements in primitive, sulfur-poor magmas, suggesting they could be metal-saturated.
KW - Gold
KW - Highly siderophile elements
KW - Iridium
KW - Olivine
KW - Osmium
KW - Partitioning
KW - Platinum group elements
UR - http://www.scopus.com/inward/record.url?scp=24344479265&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=24344479265&partnerID=8YFLogxK
U2 - 10.1016/j.epsl.2005.06.051
DO - 10.1016/j.epsl.2005.06.051
M3 - Article
AN - SCOPUS:24344479265
SN - 0012-821X
VL - 237
SP - 855
EP - 872
JO - Earth and Planetary Sciences Letters
JF - Earth and Planetary Sciences Letters
IS - 3-4
ER -