TY - JOUR
T1 - The solubility of palladium and ruthenium in picritic melts
T2 - 2. The effect of sulfur
AU - Laurenz, Vera
AU - Fonseca, Raúl O.C.
AU - Ballhaus, Chris
AU - Jochum, Klaus Peter
AU - Heuser, Alexander
AU - Sylvester, Paul J.
N1 - Funding Information:
We thank Bélinda Godel, Etienne Médard and an anonymous reviewer for their constructive reviews that helped to improve the manuscript, as well as Mark Rehkämper for his editorial handling. We are indebted to Brigitte Stoll, Ulrike Weis (MPI, Mainz, Germany), and Mike Tubrett (MUN, St. John’s, Canada) for their invaluable assistance in LA-ICP-MS work. Hugh O’Neill is thanked for fruitful discussions. We are also grateful to Henrik Blanchard, Andreas Vogt, Herbert Phiesel and Dieter Lülsdorf for maintaining the 1-atm lab in excellent running order, as well as Nils Jung for sample preparation. Harald Euler and Bruno Barbier are thanked for XRD analyses. Financial support by the DFG to Chris Ballhaus (Grant No. Ba 964/26 ) and to Raul Fonseca ( FO 698/1-1 ) is acknowledged.
PY - 2013/5/1
Y1 - 2013/5/1
N2 - The platinum-group elements (PGE) are exceptional tracers of planetary differentiation and therefore are useful discriminants of different high-temperature processes. Many of the initial efforts to understand how PGE behave during mantle melting involved experiments where PGE solubility in silicate melt was measured. The results of these experiments showed that PGE dissolve in silicate melts as oxide species, and that their saturation depends on oxygen partial pressure (pO2). However, the majority of these experimental studies were conducted on FeO and sulfur-free melt compositions that little resemble natural magmas. In particular, the role of sulfur has been downplayed because of its lower availability as a ligand to the PGE in silicate melt when compared to oxygen. However, magmatic sulfides from oceanic basalts and layered intrusions are greatly enriched in the PGE relative to the silicate melts in equilibrium with them, suggesting that the PGE are strongly chalcophile. The question then is whether the PGE are actively scavenged into sulfide melt after it exsolves from a silicate melt; or if the PGE are already associated with S2- in a silicate melt prior to sulfide saturation.Here we report the results of experiments where the solubilities of Ru and Pd have been measured in natural picritic melt, as a function of pO2 and in the presence of sulfur. Results show that the presence of sulfur in the silicate melt enhances the solubility of Ru in picrite by over an order of magnitude. These results can be used to quantify the preference that PGE have to associate with sulfur relative to oxygen. For example, Ru was found to be 880±410 times more likely to associate with sulfur than with oxygen at pO2 around the fayalite-magnetite-quartz redox equilibrium. The preferential association of the PGE with S2- ligand indicates that once a sulfide melt exsolves, it will already be enriched in PGE precluding the need for it to actively scavenge PGE from a silicate melt.
AB - The platinum-group elements (PGE) are exceptional tracers of planetary differentiation and therefore are useful discriminants of different high-temperature processes. Many of the initial efforts to understand how PGE behave during mantle melting involved experiments where PGE solubility in silicate melt was measured. The results of these experiments showed that PGE dissolve in silicate melts as oxide species, and that their saturation depends on oxygen partial pressure (pO2). However, the majority of these experimental studies were conducted on FeO and sulfur-free melt compositions that little resemble natural magmas. In particular, the role of sulfur has been downplayed because of its lower availability as a ligand to the PGE in silicate melt when compared to oxygen. However, magmatic sulfides from oceanic basalts and layered intrusions are greatly enriched in the PGE relative to the silicate melts in equilibrium with them, suggesting that the PGE are strongly chalcophile. The question then is whether the PGE are actively scavenged into sulfide melt after it exsolves from a silicate melt; or if the PGE are already associated with S2- in a silicate melt prior to sulfide saturation.Here we report the results of experiments where the solubilities of Ru and Pd have been measured in natural picritic melt, as a function of pO2 and in the presence of sulfur. Results show that the presence of sulfur in the silicate melt enhances the solubility of Ru in picrite by over an order of magnitude. These results can be used to quantify the preference that PGE have to associate with sulfur relative to oxygen. For example, Ru was found to be 880±410 times more likely to associate with sulfur than with oxygen at pO2 around the fayalite-magnetite-quartz redox equilibrium. The preferential association of the PGE with S2- ligand indicates that once a sulfide melt exsolves, it will already be enriched in PGE precluding the need for it to actively scavenge PGE from a silicate melt.
UR - http://www.scopus.com/inward/record.url?scp=84875145949&partnerID=8YFLogxK
U2 - 10.1016/j.gca.2013.01.013
DO - 10.1016/j.gca.2013.01.013
M3 - Article
AN - SCOPUS:84875145949
SN - 0016-7037
VL - 108
SP - 172
EP - 183
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
ER -