An Experimental Study of the Sulfur Content in Basaltic Melts Saturated with Immiscible Sulfide or Sulfate Liquids at 1300°C and 1·0 GPa
An Experimental Study of the Sulfur Content in Basaltic Melts Saturated with Immiscible Sulfide or Sulfate Liquids at 1300°C and 1·0 GPa
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DOI：
10.1093/petrology/egh097
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发表时间：
2004-12
影响因子：
3.9
通讯作者：
P. Jugo;R. Luth;J. Richards
中科院分区：
文献类型：
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作者：
P. Jugo;R. Luth;J. Richards
实验测定了与硫化物或硫酸盐熔体共存的玄武岩熔体中的硫含量。实验条件为13 0 0~135 5�C和1�0~1�6 Gpa，适合俯冲带以上上地幔熔融。在这种条件下，硫化物和硫酸盐都以不相容的液体形式存在，这是从硫化物和硫酸盐相的圆形几何形状推断出来的。在饱和硫酸盐液体的玄武岩熔体中测得的S含量([S]≈1�5�0�2 wt%)比饱和硫化物液体的玄武岩熔体中的S含量([S]≈0�14�0�02 wt%)高10倍。在我们的实验中，硫酸盐液体在低fO2下是稳定的，低至dfmq1�85[dfmq(FO2)Sample-log(FO2)fmq，其中fmq是铁沸石-磁铁矿-石英氧缓冲液]，来自其他来源的证据表明，在二氧化硅活度较低的熔体中，硫酸盐在低fO2下将是稳定的。由于亲硫元素和高度亲铁元素，如铜、镍、金和钯，优先分配到硫化物相中，充分氧化的硫化物不稳定的来源的熔融将有利于这些元素进入所产生的硅酸盐熔体。这种熔体将有更高的潜力产生矿藏。这项研究表明，这种氧化玄武岩的高硫含量还意味着，相对少量的这种岩浆可以提供大量的硫来溶解挥发相，并解释了一些火山喷发，如1991年皮纳图博火山喷发时排出的大部分硫。
The sulfur content in basaltic melts coexisting with either sulfide or sulfate melts was determined experimentally. The experimental conditions were in the range of 1300–1355 � C and 1� 0– 1� 6GPa, conditions appropriate for the melting of the upper mantle above subduction zones. Under these conditions, both sulfide and sulfate were present as immiscible liquids, as inferred from the round geometries of the quenched sulfide and sulfate phases. The measured S content in basaltic melts saturated with sulfate liquids ([S] ¼ 1� 5 � 0� 2 wt %) was 10 times higher than the S content in basaltic melts saturated with sulfide liquids ([S] ¼ 0� 14 � 0� 02 wt %). In our experiments, sulfate liquids were stable at fO2 as low as DFMQ ¼þ 1� 85 [DFMQ ¼ log (fO2)sample – log (fO2)FMQ, where FMQ is the fayalite–magnetite–quartz oxygen buffer], and evidence from other sources indicates that sulfates will be stable at lower fO2 in melts with lower activities of silica. Because chalcophile and highly siderophile elements, such as Cu, Ni, Au, and Pd, are partitioned preferentially into sulfide phases, melting of sufficiently oxidized sources, in which sulfides are not stable, would favor incorporation of these elements into the silicate melt produced. Such melts would have a higher potential to generate ore deposits. This study shows that the high sulfur contents of such oxidized basalts also means that relatively small amounts of such magmas can provide significant amounts of sulfur to exsolving volatile phases and account for the bulk of the sulfur expelled in some volcanic eruptions, such the 1991 eruption of Mount Pinatubo.