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首页> 外文期刊>Contributions to Mineralogy and Petrology >Behaviour of Fe4O5-Mg2Fe2O5 solid solutions and their relation to coexisting Mg-Fe silicates and oxide phases
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Behaviour of Fe4O5-Mg2Fe2O5 solid solutions and their relation to coexisting Mg-Fe silicates and oxide phases

机译：Fe4O5-Mg2Fe2O5固体溶液的行为及其与共存Mg-Fe硅酸盐和氧化术的关系

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摘要

Experiments at high pressures and temperatures were carried out (1) to investigate the crystal-chemical behaviour of Fe4O5-Mg2Fe2O5 solid solutions and (2) to explore the phase relations involving (Mg, Fe)(2)Fe2O5 (denoted as O-5-phase) and Mg-Fe silicates. Multi-anvil experiments were performed at 11-20 GPa and 1100-1600 degrees C using different starting compositions including two that were Si-bearing. In Si-free experiments the O-5-phase coexists with Fe2O3, hp-(Mg, Fe)Fe2O4, (Mg, Fe)(3)Fe4O9 or an unquenchable phase of different stoichiometry. Si-bearing experiments yielded phase assemblages consisting of the O-5-phase together with olivine, wadsleyite or ringwoodite, majoritic garnet or Fe3+-bearing phase B. However, (Mg, Fe) 2Fe2O5 does not incorporate Si. Electron microprobe analyses revealed that phase B incorporates significant amounts of Fe2+ and Fe3+ (at least similar to 1.0 cations Fe per formula unit). Fe-L-2,L-3-edge energy-loss near-edge structure spectra confirm the presence of ferric iron [Fe3+/Fe-tot = similar to 0.41(4)] and indicate substitution according to the following charge-balanced exchange: [4]Si4+ + [6]Mg2+ = 2Fe(3+). The ability to accommodate Fe2+ and Fe3+ makes this potential "water-storing" mineral interesting since such substitutions should enlarge its stability field. The thermodynamic properties of Mg2Fe2O5 have been refined, yielding H degrees(1bar, 298) = -1981.5 kJ mol(-1). Solid solution is complete across the Fe4O5-Mg2Fe2O5 binary. Molar volume decreases essentially linearly with increasing Mg content, consistent with ideal mixing behaviour. The partitioning of Mg and Fe2+ with silicates indicates that (Mg, Fe) 2Fe2O5 has a strong preference for Fe2+. Modelling of partitioning with olivine is consistent with the O-5-phase exhibiting ideal mixing behaviour. Mg-Fe2+ partitioning between (Mg, Fe)(2)Fe2O5 and ringwoodite or wadsleyite is influenced by the presence of Fe3+ and OH incorporation in the silicate phases.
机译：进行高压和温度的实验（1），研究Fe4O5-Mg2Fe2O5固溶体的晶体化学行为和（2）探讨涉及（Mg，Fe）（2）Fe2O5的相位关系（表示为O-5 - 相）和Mg-Fe硅酸盐。使用不同的起始组合物在11-20GPa和1100-1600摄氏度下进行多脂族实验，其中包括两个轴承。在Si-Fee实验中，O-5相与Fe 2 O 3，HP-（Mg，Fe）Fe 2 O 4，（Mg，Fe）（3）Fe4O9或不同化学计量的未容量相位的共存。 Si-轴承实验产生了由O-5相和橄榄石，鲸类矿石或英茅斯，吉米菌素或Fe3 + + + Bearing阶段B组成的相位组合。然而，（Mg，Fe）2Fe2O5不含Si。电子微探针分析显示，相B含有大量的Fe2 +和Fe 3 +（至少与每配方单元的1.0阳离子Fe相似）。 FE-L-2，L-3边 - 边缘能量损失近边缘结构光谱确认存在铁铁[Fe3 + / Fe-Tot =类似于0.41（4）]，并根据以下电荷平衡交换表示替代：[4] Si4 + + [6] Mg2 + = 2Fe（3+）。容纳Fe2 +和Fe3 +的能力使得这种潜在的“水资源存放”矿物有趣，因为这些替换应该扩大其稳定场。 Mg2Fe2O5的热力学性质已被精制，得到H度（1bar，298）= -1981.5kJ摩尔（-1）。在Fe4O5-Mg2Fe2O5二进制中完成固溶体。摩尔体积基本上随着Mg含量的增加而降低，与理想的混合行为一致。用硅酸盐的Mg和Fe2 +的分配表明（Mg，Fe）2Fe2O5对Fe2 +具有强烈偏好。用橄榄石分配的建模与表现出理想混合行为的O-5相符一致。 （Mg，Fe）（2）Fe2O5和Ringwoodite或Wadsleyite之间的Mg-Fe2 +分配受Fe3 +和OH掺入硅酸盐相的影响。

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