The solubility of palladium and ruthenium in picritic melts: 2. The effect of sulfur
The solubility of palladium and ruthenium in picritic melts: 2. The effect of sulfur
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DOI：
10.1016/j.gca.2013.01.013
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发表时间：
2013-05-01
影响因子：
5
通讯作者：
Sylvester, Paul J.
中科院分区：
文献类型：
--
作者：
Laurenz, Vera;Fonseca, Raul O. C.;Sylvester, Paul J.
铂族元素（PGE）是行星分化的特殊示踪剂，因此是不同高温过程的有用判别因子。为了了解 PGE 在地幔熔化过程中的行为，许多最初的努力都涉及测量 PGE 在硅酸盐熔体中溶解度的实验。这些实验的结果表明，PGE 以氧化物形式溶解在硅酸盐熔体中，并且其饱和度取决于氧分压 (pO(2))。然而，这些实验研究大部分是针对与天然岩浆不太相似的 FeO 和无硫熔体成分进行的。特别是，硫的作用已被淡化，因为与氧相比，硫作为硅酸盐熔体中 PGE 配体的可用性较低。然而，来自大洋玄武岩和层状侵入体的岩浆硫化物在 PGE 中相对于与其平衡的硅酸盐熔体而言大大富集，这表明 PGE 具有强亲铜性。那么问题是 PGE 从硅酸盐熔体中溶出后是否会被主动清除到硫化物熔体中？或者，如果 PGE 在硫化物饱和之前已经与硅酸盐熔体中的 S2- 缔合。在这里，我们报告了实验结果，其中在天然苦味酸熔体中测量了 Ru 和 Pd 的溶解度，作为 pO(2) 的函数并在硫存在的情况下。结果表明，硅酸盐熔体中硫的存在使钌在苦味石中的溶解度提高了一个数量级以上。这些结果可用于量化 PGE 相对于氧与硫的关联偏好。例如，在铁橄榄石-磁铁矿-石英氧化还原平衡附近的 pO(2) 条件下，发现 Ru 与硫缔合的可能性比与氧缔合的可能性高 880 +/- 410 倍。 PGE与S2-配体的优先结合表明，一旦硫化物熔体溶出，它就已经富含PGE，从而排除了它从硅酸盐熔体中主动清除PGE的需要。 (C) 2013 Elsevier Ltd. 保留所有权利。
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 (pO(2)). 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 pO(2) 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 pO(2) 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. (C) 2013 Elsevier Ltd. All rights reserved.