The dependence of the partitioning of iron and europium between plagioclase and hydrous tonalitic melt on oxygen fugacity
The dependence of the partitioning of iron and europium between plagioclase and hydrous tonalitic melt on oxygen fugacity
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DOI：
10.1007/s004100050585
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发表时间：
1999-10
影响因子：
3.5
通讯作者：
M. Wilke;H. Behrens
中科院分区：
文献类型：
--
作者：
M. Wilke;H. Behrens
研究了SiO_2（Q_2）-NaAlSi_3O_8（Ab）-CaAl_2Si_2O_8（An）-H_2O体系中Fe和Eu在斜长石和熔体间的分配与氧逸度的关系。实验在500 MPa和850 °C/750 °C下在水饱和条件下进行。氧逸度在logfO 2-范围内变化，从−7.27到−15.78。为了在最还原的条件下工作，对经典的双胶囊技术进行了修改。将样品和C-O-H轴承传感器胶囊彼此相邻地放置在BN夹套内，以使氢到容器气氛中的损失最小化。通过这种设置，即使在96小时的运行中，也可以保持比FeO-Fe_3 O_4缓冲液稍微更还原的氧化还原条件。拉曼光谱表明，BN通过与氢反应而改性，导致低的氢渗透性。在850 °C和500 MPa下测定的Eu的分配系数从Cu-Cu 2 O缓冲条件下的0.095变化到最还原条件下的1.81（C-O-H传感器）。在相同的fO 2区间内，Fe的分配系数从氧化条件下的0.55变化到最还原条件下的0.08。Sm的分配，这是作为一个三价稀土元素的参考，不随氧逸度，产生的平均值福特= 0.07。对于一定的fO 2，将温度降低到750 °C，降低Eu的分配系数，增加Fe的分配系数。在1个大气压和在更高的温度下与已公布的数据的比较表明，温度和组成的熔体上的分配行为有很强的影响。由于Eu和Fe在与地质有关的fO 2范围内的分配系数变化很大，因此Eu和Fe的分配系数可用来估计火成岩成因的氧化还原条件。此外，通过对分配数据进行建模，可以提取关于熔体的氧化还原状态的信息。由此产生的铁-铁的比率显示出显着的差异，从经验模型预测。
The dependence of iron and europium partitioning between plagioclase and melt on oxygen fugacity was studied in the system SiO2(Qz)—NaAlSi3O8(Ab)—CaAl2Si2O8(An)—H2O. Experiments were performed at 500 MPa and 850 °C/750 °C under water saturated conditions. The oxygen fugacity was varied in the logfO2-range from −7.27 to −15.78. To work at the most reducing conditions the classical double-capsule technique was modified. The sample and a C—O—H bearing sensor capsule were placed next to each other within a BN jacket to minimise loss of hydrogen to the vessel atmosphere. By this setup redox conditions slightly more reducing than the FeO—Fe3O4buffer could be maintained even in 96 h runs. Raman spectra showed that the BN was modified by reaction with hydrogen resulting in a low hydrogen permeability. The partition coefficients determined for Eu at 850 °C and 500 MPa vary from 0.095 at conditions of the Cu—Cu2O buffer to 1.81 at the most reducing conditions (C—O—H sensor). In the samefO2interval the partition coefficient for Fe varies from 0.55 at oxidising conditions to 0.08 at the most reducing conditions. The partitioning of Sm, which was added as a reference for a trivalent REE, does not vary with the oxygen fugacity, yielding an average value forD= 0.07. Lowering the temperature to 750 °C for a givenfO2decreases the partition coefficient of Eu and increases that of Fe. Comparison with published data at 1 atm and at higher temperatures shows that both temperature and composition of the melt have strong effects on the partitioning behaviour. As the change of the partition coefficients in the geologically relevantfO2range is quite strong, element partitioning of Eu and Fe might be used to estimate redox conditions for the genesis of igneous rocks. Furthermore, by modelling the partitioning data it is possible to extract information about the redox state of the melt. Resulting ferric-ferrous ratios show significant differences from those predicted by empirical models.