Abstract We develop a new method to quantify the reducing capacity (ΔO2) of a wide range of geological materials. The protocol consists in a high temperature chalcometric titration by which a known amount of pure O2 gas is exchanged between an oxygen donor, CuO, and an oxygen acceptor, the sample, at elevated temperature. Calibration of the method using elemental C, native S and magnetite demonstrates that the method effectively oxidizes C, S and Fe to their terminal oxidation state, C4+, S6+ and Fe3+, respectively. Moreover, because the metric is independent of pressure and temperature, it provides a measure that can be used for quantitative assessments of redox fluxes in open geological systems. Preliminary results suggest that the specific reducing capacity, dO2, of geological materials span many orders of magnitude, ranging from less than 300 μmol O2/g for ultramafic rocks and tholeiitic basalts, to more than 0.1 mol O2/g for black shales. This highlights a counterintuitive, and yet physically consistent, characteristic of the redox structure of our planet. Rocks characterized by elevated dO2 values are ubiquitous at the Earth surface, while the upper mantle and lower crust are typically composed of rocks with much lower dO2. This work will contribute to provide a more nuanced and complete perspective on the redox structure of the Earth and its evolution.

中文翻译：

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用高温硫醚滴定法降低岩石的容量

摘要 我们开发了一种新方法来量化各种地质材料的还原能力 (ΔO2)。该协议包括高温硫醚滴定，通过该滴定，已知数量的纯 O2 气体在氧供体 CuO 和氧受体（样品）之间在升高的温度下进行交换。使用元素 C、天然 S 和磁铁矿校准该方法表明，该方法有效地将 C、S 和 Fe 分别氧化为它们的末端氧化态 C4+、S6+ 和 Fe3+。此外，由于该指标与压力和温度无关，因此它提供了一种可用于定量评估开放地质系统中氧化还原通量的度量。初步结果表明，地质材料的比还原能力 dO2 跨越多个数量级，从超基性岩和拉斑玄武岩的小于 300 μmol O2/g 到黑色页岩的大于 0.1 mol O2/g。这突出了我们星球氧化还原结构的一个违反直觉但物理上一致的特征。以 dO2 值升高为特征的岩石在地球表面无处不在，而上地幔和下地壳通常由 dO2 值低得多的岩石组成。这项工作将有助于对地球的氧化还原结构及其演化提供更细致、更完整的视角。而上地幔和下地壳通常由 dO2 低得多的岩石组成。这项工作将有助于对地球的氧化还原结构及其演化提供更细致、更完整的视角。而上地幔和下地壳通常由 dO2 低得多的岩石组成。这项工作将有助于对地球的氧化还原结构及其演化提供更细致、更完整的视角。