Sulfur degassing at Erta Ale (Ethiopia) and Masaya (Nicaragua) volcanoes: Implications for degassing processes and oxygen fugacities of basaltic systems
Sulfur degassing at Erta Ale (Ethiopia) and Masaya (Nicaragua) volcanoes: Implications for degassing processes and oxygen fugacities of basaltic systems
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DOI：
10.1002/ggge.20255
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发表时间：
2013-10-01
影响因子：
3.5
通讯作者：
Kelley, K. A.
中科院分区：
文献类型：
--
作者：
de Moor, J. M.;Fischer, T. P.;Kelley, K. A.
我们调查了埃尔塔阿莱和马萨亚火山的硫逸度和氧逸度之间的关系。氧逸度进行了评估，利用Fe 3 +/西格玛铁和主要元素组成的橄榄石托管熔体包裹体和基质玻璃测量。Erta Ale熔体的Fe 3 +/Sigma Fe为0.15-0.16，反映了Delta QFM 0.0 +/-0.3的fO（2），这与根据高温气体中的CO2/CO比率计算的fO（2）无法区分。马萨亚在Delta QFM + 1.7 +/- 0.4时氧化程度更高，这是典型的电弧设置。二塔阿勒火山气体和火山渣的硫同位素组成（δ S-34（气体）-千分之0.5; δ S-34（火山渣）+千分之0.9）和马萨亚（delta S-34（气体）+4.8ppm; δ S-34（矿渣）+7.4ppm）反映了不同的硫源，以及脱气过程中的同位素分馏（平衡和动力学分馏效应）。熔体中硫的形态对脱气过程中的同位素分馏起着重要作用，马萨亚熔体包裹体中S ~（6+）/σ S = 0.67。在Erta Ale处，随着S脱气的程度，没有观察到Fe 3 +/Sigma Fe或S6+/Sigma S的变化，这表明对fO（2）的影响可以忽略不计，并且进一步表明H2S是从富含S2的熔体中溶出的主要气体种类（即，没有电子的再分布）。在Erta Ale气体排放中观察到的高SO2/H2S是由于在低压和固定fO（2）下的气体再平衡。硫预算的考虑表明，大部分的S注入到系统中的气体排放，因此，这是岩浆S同位素组成的代表。马萨亚气体羽流的成分（+4.8 ‰）不能用分馏效应来解释，而是反映了高δ S-34氧化硫通过俯冲带的再循环。
We investigate the relationship between sulfur and oxygen fugacity at Erta Ale and Masaya volcanoes. Oxygen fugacity was assessed utilizing Fe3+/Sigma Fe and major element compositions measured in olivine-hosted melt inclusions and matrix glasses. Erta Ale melts have Fe3+/Sigma Fe of 0.15-0.16, reflecting fO(2) of Delta QFM 0.0 +/- 0.3, which is indistinguishable from fO(2) calculated from CO2/CO ratios in high-temperature gases. Masaya is more oxidized at Delta QFM + 1.7 +/- 0.4, typical of arc settings. Sulfur isotope compositions of gases and scoria at Erta Ale (delta S-34(gas) - 0.5 parts per thousand; delta S-34(scoria) + 0.9 parts per thousand) and Masaya (delta S-34(gas) + 4.8 parts per thousand; delta S-34(scoria) + 7.4 parts per thousand) reflect distinct sulfur sources, as well as isotopic fractionation during degassing (equilibrium and kinetic fractionation effects). Sulfur speciation in melts plays an important role in isotope fractionation during degassing and S6+/Sigma S is 0.67 in Masaya melt inclusions. No change is observed in Fe3+/Sigma Fe or S6+/Sigma S with extent of S degassing at Erta Ale, indicating negligible effect on fO(2), and further suggesting that H2S is the dominant gas species exsolved from the S2--rich melt (i.e., no redistribution of electrons). High SO2/H2S observed in Erta Ale gas emissions is due to gas re-equilibration at low pressure and fixed fO(2). Sulfur budget considerations indicate that the majority of S injected into the systems is emitted as gas, which is therefore representative of the magmatic S isotope composition. The composition of the Masaya gas plume (+4.8 parts per thousand) cannot be explained by fractionation effects but rather reflects recycling of high delta S-34 oxidized sulfur through the subduction zone.