On the P-T fO2 stability of Fe4O5, Fe5O6 and Fe4O5-rich solid solutions
On the P-T fO2 stability of Fe4O5, Fe5O6 and Fe4O5-rich solid solutions
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DOI：
10.1007/s00410-016-1258-4
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发表时间：
2016-05-01
影响因子：
3.5
通讯作者：
Miyajima, Nobuyoshi
中科院分区：
文献类型：
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作者：
Myhill, Robert;Ojwang, Dickson O.;Miyajima, Nobuyoshi
高压相Fe4O5和Fe506最近被添加到已知的氧化铁列表中。作为混合价相，有人认为，一旦主要矿物在铁中饱和，它们可能在地幔中形成。Fe4O5与Mg2+和Cr3+形成广泛的固溶体，也支持了Fe4O5在地幔中存在的可能性。在这项研究中，我们介绍了在1000-1400℃下，在5 - 24 GPa范围内进行的高压和高温多砧实验的结果，旨在限制Fe4O5相的稳定场。我们将这些结果与已发表的相平衡、状态方程和Fe - Mg分配数据结合起来，估计了Fe4O5、Fe5O6和（Mg,Fe）(2)Fe2O5固溶体的热力学性质。利用热力学模型，计算了高压铁氧化物稳定时的氧逸度，计算了（Mg,Fe）(2)Fe2O5在橄榄石和辉石组合中的氧化还原稳定性，并将其作为体积Fe/(Fe + Mg)比的函数。Fe4O5和（Mg,Fe）(2)Fe2O5在氧逸度高于金刚石稳定场时是稳定的，因此不太可能在金刚石中发现包裹体。另一方面，Fe5O6的稳定场扩展到与金刚石形成相容的氧逸度。利用Mg - Fe固溶体模型，我们发现fe4o5结构相将局限于地幔中的贫铝环境，如通过俯冲进入地幔的褐铁矿或富含二氧化硅氧化铁的沉积物。
The high-pressure phases Fe4O5 and Fe506 have recently been added to the list of known iron oxides. As mixed -valence phases, it has been suggested that they could form in the Earth's mantle once the dominant minerals become saturated in ferric iron. The possibility that Fe4O5 could exist in the mantle is also supported by the fact that it forms extensive solid solutions with both Mg2+ and Cr3+. In this study, we present the results of high-pressure and high-temperature multi -anvil experiments performed between 5 and 24 GPa at 1000-1400 degrees C aimed at constraining the stability field of the Fe4O5 phase. We combine these results with published phase equilibria, equation of state and Fe Mg partitioning data to estimate the thermodynamic properties of Fe4O5, Fe5O6 and the (Mg,Fe)(2)Fe2O5 solid solution. Using our thermodynamic model, the oxygen fugacity at which the high-pressure iron oxides become stable is calculated and the redox stability of (Mg,Fe)(2)Fe2O5 in an assemblage of olivine and pyroxene is calculated as a function of the bulk Fe/(Fe + Mg) ratio. Fe4O5 and (Mg,Fe)(2)Fe2O5 are stable at oxygen fugacities higher than the diamond stability field and are, therefore, unlikely to be found as inclusions in diamonds. The stability field of Fe5O6, on the other hand, extends to oxygen fugacities compatible with diamond formation. Using the Mg Fe solid solution model, we show that Fe4O5-structured phases would be restricted to aluminium -poor environments in the mantle such as dunites or silica iron oxide rich sediments transported into the mantle via subduction.