Direct measurements of copper speciation in basaltic glasses: understanding the relative roles of sulfur and oxygen in copper complexation in melts
Direct measurements of copper speciation in basaltic glasses: understanding the relative roles of sulfur and oxygen in copper complexation in melts
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DOI：
10.1016/j.gca.2019.09.029
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发表时间：
2019-12-15
影响因子：
5
通讯作者：
Wallace, Paul J.
中科院分区：
文献类型：
--
作者：
Lanzirotti, Antonio;Lee, Lopaka;Wallace, Paul J.
微量分析测定的铜（Cu）形态的天然岩浆玻璃，下面的镍-氧化镍（NNO）缓冲液平衡，揭示了两个铜物种通常是稳定的玄武岩熔体。对大洋中脊玄武岩（MORB）、Nyamuragira、埃特纳和基拉韦厄火山的玄武岩基质玻璃和熔体包裹体的X射线吸收精细结构（XAFS）光谱分析表明，硅酸盐熔体中的Cu络合物既有Cu（I）-硫化物，也有Cu（I）-氧化物。每种物质的比例与玻璃中测得的硫（S）丰度相关。在玻璃中的S丰度大于类似于1000 ppm，铜（I）-硫化物物种是占主导地位的，而在玻璃中的S丰度在500和1000 ppm之间，这两个物种被发现共存。Cu（I）-氧化物物种在低于500 ppm的S浓度下占主导地位。在我们分析的1 atm无S玄武岩组成的实验玻璃中，仅Cu（I）-氧化物物种是可检测的，而不管氧逸度（fO（2）），即使在远高于NNO缓冲区的相对高的fO（2）值下。我们的研究结果表明，XAFS技术是高度敏感的测量还原（NNO以下）玄武玻璃中的铜形态，氧化物和硫化物络合物可以稳定。这两种物质的相对比例高度依赖于熔体中S的浓度，因此随着低压脱气从熔体中损失S，自然熔体中Cu的形态发生变化。(C)2019爱思唯尔有限公司版权所有。
Micro-analytical determination of copper (Cu) speciation in natural magmatic glasses, equilibrated below the nickel - nickel oxide (NNO) buffer, reveals that two copper species are commonly stabilized in such basaltic melts. X-ray absorption fine structure (XAFS) spectroscopic analysis of basaltic matrix glasses and melt inclusions (MI) from samples of mid-ocean ridge basalt (MORB), and from Nyamuragira, Etna and Kilauea volcanoes shows that Cu complexes as both Cu(I)-sulfide and Cu (I)-oxide species in silicate melts. The proportion of each species correlates with the measured sulfur (S) abundance of the glass. In glasses with S abundances greater than similar to 1000 ppm, Cu(I)-sulfide species are dominant, whereas in glasses with S abundances between 500 and 1000 ppm, both species are found to coexist. The Cu(I)-oxide species dominate at S concentrations below 500 ppm. In 1 atm S-free experimental glasses of basaltic composition that we analyzed, only Cu(I)-oxide species are detectable, regardless of the oxygen fugacity (fO(2)), even at relatively high fO(2) values well above the NNO buffer. Our results demonstrate that XAFS techniques are highly sensitive in measuring Cu speciation in reduced (below NNO) basaltic glasses and that both oxide and sulfide complexes can be stabilized. The relative proportion of these two species is highly dependent on the concentration of S in the melt, and thus the Cu speciation in natural melts changes as S is lost from the melt by low pressure degassing. (C) 2019 Elsevier Ltd. All rights reserved.