The partitioning of sulfur and chlorine between andesite melts and magmatic volatiles and the exchange coefficients of major cations
The partitioning of sulfur and chlorine between andesite melts and magmatic volatiles and the exchange coefficients of major cations
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DOI：
10.1016/j.gca.2012.04.039
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发表时间：
2012-07
影响因子：
5
通讯作者：
Z. Zajacz;P. Candela;P. Piccoli;C. Sanchez‐Valle
中科院分区：
文献类型：
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作者：
Z. Zajacz;P. Candela;P. Piccoli;C. Sanchez‐Valle
安山岩熔体平衡与H-O-S轴承挥发相，以确定分配系数为S和Cl作为熔体组成和氧逸度的函数。实验在200 MPa和1000°C下在快速淬火MHC容器组件中进行，并且在NNO−1.2和NNO+1.8之间的强加fO 2范围内进行。采用高流体/熔体质量比（0.15），可以通过质量平衡计算获得精确且准确的分配系数。氯在ClO− 0.5活度下表现出亨利行为，这是典型的弧岩浆，DCl挥发/熔融=1.36±0.06（1σ）低于0.2wt.%熔体中的Cl;在较高的ClO− 0.5活性下，DClvolatile/熔体在1 wt.%时线性增加至2.11±0.02熔体中的氯。在挥发相中：FeCl_2> NaCl>KCl> HCl。测定了主要阳离子的阳离子交换系数：KK，Navolatile/melt=1.23±0.10（1σ）和KFe，Navolatile/melt= DF，Navolatile/melt/DNNavolatile/melt=1.08±0.16（1σ）。在此条件下，HCl在蒸汽中的浓度与熔体中的（Na+K）/（Al+ Fe 3+）比值呈负相关。在低于磁黄铁矿饱和度的fH 2S条件下，安山岩熔体-挥发体系中的还原硫（S2−）似乎遵循亨利定律。在fO 2 =NNO-0.5时，S的分配系数与熔体中FeO的浓度呈负相关，在4.0wt.%时为254±25 FeO至88±6（7.5wt.%）FeO。当挥发相中的硫含量约为3.2mol%时，磁黄铁矿达到饱和，此时fO 2 =NNO−0.5。当FeO含量为1.6wt.%时，在硫化物/硫酸盐转变时，S的分配系数从171±23下降到21±1在融化。当fO_2 =NNO+1.8时，挥发相中S的含量为0.33mol%时，硬石膏达到饱和。中基性岩浆溶出的水溶性挥发分能有效地提取硫，并影响硫向岩浆热液成矿存款场所的迁移。
Andesite melts were equilibrated with an H–O–S-bearing volatile phase to determine the partition coefficients for S and Cl as a function of melt composition and oxygen fugacity. The experiments were conducted in rapid-quench MHC vessel assemblies at 200MPa and 1000°C, and over a range of imposed fO2between NNO−1.2 and NNO+1.8. High fluid/melt mass ratios (∼15) were employed, allowing precise and accurate partition coefficients to be obtained by mass balance calculations. Chlorine exhibits Henrian behavior at ClO−0.5activities typical for arc magmas, with DClvolatile/melt=1.36±0.06 (1σ) below 0.2wt.% Cl in the melt; at higher ClO−0.5activities, DClvolatile/meltincreases linearly to 2.11±0.02 at 1wt.% Cl in the melt. In the volatile phase: FeCl2∼NaCl>KCl∼HCl. The determination of cation exchange coefficients for major cations yielded: KK,Navolatile/melt=1.23±0.10 (1σ) and∗KFe,Navolatile/melt=DFevolatile/melt/DNavolatile/melt=1.08±0.16 (1σ). Under these conditions, the concentration of HCl in the vapor is negatively correlated with the (Na+K)/(Al+Fe3+) ratio in the melt. Reduced sulfur (S2−) appears to obey Henry’s law in andesite melt–volatile system at fH2S below pyrrhotite saturation. The partition coefficient for S at fO2=NNO−0.5 correlates negatively with the FeO concentration in the melt, changing from 254±25 at 4.0wt.% FeO to 88±6 at 7.5wt.% FeO. Pyrrhotite saturation is reached when approximately 3.2mol% S is present in the volatile phase at fO2=NNO−0.5. At the sulfide/sulfate transition, the partition coefficient of S drops from 171±23 to 21±1 at a constant FeO content of ∼6wt.% in the melt. At fO2=NNO+1.8, anhydrite saturation is reached at ∼3.3mol% S present in the volatile phase. Aqueous volatiles exsolving from intermediate to mafic magmas can efficiently extract S, and effect its transfer to sites of magmatic-hydrothermal ore deposit formation.