Loss of iron to gold capsules in rock-melting experiments
Loss of iron to gold capsules in rock-melting experiments
复制标题
岩石熔化实验中铁损失为金胶囊
DOI：
10.2138/am-1999-1005
复制
发表时间：
1999
影响因子：
3.1
通讯作者：
T. Sisson
中科院分区：
文献类型：
--
作者：
K. Ratajeski;T. Sisson
摘要金被广泛用于高温岩石熔融研究中的胶囊，因为通常认为它从硅酸盐样品中吸收的铁可以忽略不计。然而，我们观察到显着的损失，从流体熔融实验角闪石辉长岩在800-975 ℃和8千巴，使用标准的活塞缸技术。样品的Fe损失程度取决于样品和胶囊的相对质量。低样品与胶囊质量比（约0.04）导致最高的Fe损失（相对32 - 19%）。硅酸盐熔体和使用的金胶囊中的Fe浓度定义了表观平衡常数（K_（max）），其遵循线性In K_（max）与1/T关系（在QFM-1的估计log fO_（max）处）。的表观平衡常数是用来限制上限估计的Fe量，可能会失去在岩石熔化实验的范围内的fO和样品胶囊的质量比。在高fO_2（NNO + 2）下，对于宽范围的样品与胶囊质量比，Fe到金的损失是可忽略的（相对<2%）。在NNO的fO值下，通过使用0.2或更大的样品与胶囊质量比，Fe损失可以保持在<10%。在低fO值（QFM-1）下，必须用Fe预饱和Au，以确保Fe损失保持<10%。Fe损失可能会影响在低fO-条件下运行的小样品的实验结果，无论它们是缓冲的，由压力介质施加的，还是由固有还原的（石墨）起始材料产生的。
Abstract Gold is used widely for capsules in high-temperature rock-melting studies because it is generally thought to absorb negligible Fe from silicate samples. However, we observed significant losses of Fe from fluid-absent melting experiments on hornblende gabbros at 800-975 ℃ and 8 kbar, using standard piston-cylinder techniques. The extent of Fe loss from the sample is dependent on the relative masses of the sample and the capsule. Low sample to capsule mass ratios (~0.04) lead to the highest Fe losses (32 - 19% relative). Concentrations of Fe in silicate melt and used gold capsules define an apparent equilibrium constant (Kʹ) that follows a linear In Kʹ vs. 1/T relation (at an estimated log fO₂ of QFM-1). The apparent equilibrium constant is used to make limiting upper estimates on the amount of Fe that could be lost during rock-melting experiments for a range of fO₂ and sample to capsule mass ratios. At high fO₂ (NNO + 2), loss of Fe to gold is negligible (<2% relative) for a wide range of sample to capsule mass ratios. At an fO₂ of NNO, Fe loss can be kept to <10% relative by using a sample to capsule mass ratio of 0.2 or greater. At low fO₂ (QFM-1), presaturating the Au with Fe would be necessary to ensure that Fe losses remained <10% relative. Fe loss can compromise experimental results for small samples run at low fO₂ conditions, be they buffered, imposed by the pressure media, or produced by intrinsically reduced (graphitic) starting materials.