ABSTRACT The chance of apparent isotope anomalies either in closed systems at equilibrium or during Rayleigh processes is investigated. The term ‘apparent’ is chosen to highlight that only mass-dependent fractionation (MDF) processes are considered. A goal is finding analytical expressions that could be used for dealing with the complexity of real systems. For example, the formula for calculating the isotopic fractionation in systems with any desired number of phases involved is identified. Terrestrial samples could exhibit artificially low MIF signatures because Δ is not invariant with the choice of the reference material. An alternative parameter Δ* only depending on β is therefore introduced. The potential transfer of sample points in a three-isotope plot to parallel lines during reversible processes is also investigated. Larger apparent anomalies are expected in systems lacking an infinite reservoir and for large enrichment factors. Pyrite is stable beyond the conditions for a reducing environment and MIF signatures from Archaean sediments could be compatible with reversible processes involving oxidised species. Isotope anomalies in pyrite from the Dresser Formation, Australia, are compatible with post-depositional incorporation of 2–5% sulphur of atmospheric origin. Overall, observed delta values could mainly be related to changes in the local absolute isotope abundances.

中文翻译：

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关于来自平衡相分配的表观质量独立分馏 (MIF) 特征

摘要 研究了处于平衡状态的封闭系统中或瑞利过程中出现明显同位素异常的可能性。选择“明显”一词是为了强调仅考虑质量相关分馏 (MDF) 过程。一个目标是找到可用于处理真实系统复杂性的分析表达式。例如，确定了在涉及任何所需相数的系统中计算同位素分馏的公式。地面样本可能会人为地表现出较低的 MIF 特征，因为 Δ 不会随参考材料的选择而变化。因此引入了仅取决于 β 的替代参数 Δ*。还研究了可逆过程中三同位素图中的样本点向平行线的潜在转移。在缺乏无限储层和大富集因子的系统中，预计会有更大的明显异常。黄铁矿在还原环境的条件下是稳定的，来自太古代沉积物的 MIF 特征可能与涉及氧化物质的可逆过程兼容。澳大利亚德莱瑟地层黄铁矿的同位素异常与大气来源的 2-5% 硫的沉积后掺入相容。总体而言，观测到的 delta 值可能主要与当地绝对同位素丰度的变化有关。澳大利亚德莱瑟地层黄铁矿的同位素异常与大气来源的 2-5% 硫的沉积后掺入相容。总体而言，观测到的 delta 值可能主要与当地绝对同位素丰度的变化有关。澳大利亚德莱瑟地层黄铁矿的同位素异常与大气来源的 2-5% 硫的沉积后掺入相容。总体而言，观测到的 delta 值可能主要与当地绝对同位素丰度的变化有关。