A simple model for chalcophile element partitioning between sulphide and silicate liquids with geochemical applications
A simple model for chalcophile element partitioning between sulphide and silicate liquids with geochemical applications
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DOI：
10.1016/j.epsl.2013.09.034
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发表时间：
2013-12-01
影响因子：
5.3
通讯作者：
Wood, Bernard J.
中科院分区：
文献类型：
--
作者：
Kiseeva, Ekaterina S.;Wood, Bernard J.
本文测定了在高温高压下，铜、铟、铊、铅、银、锰、锌、铬、钴、镍、锑、镉等元素在富FeS硫化物液体和无水玄武岩熔体中的分配。发现硫化物液体中的氧含量与硅酸盐熔体中的FeO含量呈线性关系。我们还发现了硅酸盐熔体的FeO含量与各微量元素的硫化物-硅酸盐分配系数D-M(硫/硅)之间的简单关系。这些关系一般可表示为：logD-M(硫/硅)近似为A+n/2log[FeO]，其中A是与Fe-M交换自由能有关的常数，n是与元素价态有关的常数，[FeO]是以摩尔分数或重量百分比表示的硅酸盐熔体的FeO含量。这种简单的关系有效地消除了在考虑分区时定义逸度比f(O2)/f(S2)的需要，从而极大地简化了分区数据在自然系统中的应用。理论上，对于1+离子，n应该近似为1，对于2+离子，n应该近似为2，以此类推。N的回归值通常接近于预期的值，尽管某些元素会出现偏差。对于硫化物是FeS-NiS-Cu2S液体的情况，我们通过修正硅酸盐熔体的FeO含量获得了与纯FeS的结果很好的一致：[FeO](修正后)=[FeO](硅酸盐)/[Fe/(Fe+Ni+Cu)](硫化物)我们根据文献中的数据检验了我们的模型，其中测定了铜、钴、镍和锰的硫化物-硅酸盐分配系数。这些元素的文献数据遵循LOG D-M(硫/硅)与LOG[wt%FeO]的预测线性关系。此外，我们得到的D-M绝对值(硫/银)与文献中的值之间的差异可以从温度和基质的影响(如硫化物的Ni/Fe比)来量化。我们利用我们的结果来计算地幔部分熔融分离结晶所产生的玄武岩的Ce/Pb值和NdPb值。如果我们假设亏损地幔含有65 ppb的铅，则计算的NdPb值在较大的部分熔融和分离结晶范围内基本上是恒定的，其值类似于18.6。计算的Ce/Pb值在间歇部分熔化过程中变化不大，从21到29，在接近10%的部分熔化时达到标准值25。这些趋势与大洋玄武岩玻璃的测量结果非常一致。最后，我们利用我们的分配关系计算了亏损地幔中一些不相容的亲白微量元素的浓度。它们是：32 ppm铜、65 ppb铅、7.6 ppb Ag、12 ppb In、23 ppb Cd、1.7 ppb Sb和1.3 ppb Tl。(C)2013爱思唯尔B.V.保留所有权利。
We have determined the partitioning of the elements Cu, In, Tl, Pb, Ag, Mn, Zn, Cr, Co, Ni, Sb and Cd between FeS-rich sulphide liquids and anhydrous basaltic melts at high pressures and temperatures. The sulphide liquids were found to have oxygen contents which are linearly related to the FeO contents of the silicate melts. We also found simple relationships between the FeO contents of the silicate melts and the sulphide-silicate partition coefficients D-M(sulph/sil) for the individual trace elements. These relationships can be generally represented as follows:log D-M(sulph/sil) approximate to A + n/2 log[FeO]where A is a constant related to the free energy of Fe-M exchange, n is a constant related to the valence of the element and [FeO] is the FeO content of the silicate melt in mole fraction or weight %. This simple relationship effectively removes the need to define the fugacity ratio f(o2)/f(s2) when considering partitioning and hence greatly simplifies application of partitioning data to natural systems. In theory n should approximate 1 for 1+ ions, 2 for 2+ ions and so on. Regressed values of n are generally close to those expected, although deviations occur for some elements. The deviations can be understood in terms of the relative chalcophile and lithophile characteristics of the element of concern.For cases in which the sulphide is an FeS-NiS-Cu2S liquid we obtain excellent agreement with results for pure FeS by correcting the FeO content of the silicate melt as follows:[FeO](corrected) = [FeO](silicate)/[Fe/(Fe + Ni + Cu)](sulphide)We tested our model on data from the literature in which sulphide-silicate partition coefficients for Cu, Co, Ni and Mn were determined. Literature data for these elements follow the predicted linear dependence of log D-M(sulph/sil) on log [wt% FeO]. Furthermore, differences between the absolute values of D-M(sulph/sil) obtained by us and those in the literature are quantifiable in terms of temperature and matrix effects such as the Ni/Fe ratio of the sulphide.We used our results for Pb partitioning to calculate Ce/Pb and Nd/Pb ratios of basalts generated by partial melting of the mantle followed by fractional crystallization. Calculated Nd/Pb is essentially constant over wide ranges of partial melting and fractional crystallization with a value of similar to 18.6 if we assume that depleted mantle contains 65 ppb of Pb. Calculated Ce/Pb varies slightly during batch partial melting from 21 to 29 with the canonical value of 25 being achieved at similar to 10% partial melting. These trends are in excellent agreement with measurements of oceanic basalt glasses.Finally, we used our partitioning relationships to calculate the concentrations of a number of the incompatible chalcophile trace elements in depleted mantle. These are as follows: 32 ppm Cu, 65 ppb Pb, 7.6 ppb Ag, 12 ppb In, 23 ppb Cd, 1.7 ppb Sb and 1.3 ppb Tl. (C) 2013 Elsevier B.V. All rights reserved.