Behaviour of Fe4O5–Mg2Fe2O5 solid solutions and their relation to coexisting Mg–Fe silicates and oxide phases
Behaviour of Fe4O5–Mg2Fe2O5 solid solutions and their relation to coexisting Mg–Fe silicates and oxide phases
复制标题
Fe4O5âMg2Fe2O5 固溶体的行为及其与共存 MgâFe 硅酸盐和氧化物相的关系
DOI：
10.1007/s00410-018-1443-8
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发表时间：
2018
影响因子：
3.5
通讯作者：
Frost D
中科院分区：
文献类型：
--
作者：
Uenver-Thiele L;Woodland AB;Miyajima N;Boffa Ballaran T;Frost D
在过去的几年里，后尖晶石相引起了越来越多的关注，由于发现了几个高压（hp）氧化物相的化学计量比以外的M3 O 4。具有M4 O 5、M5 O 6和M7 O 9化学计量比的相现已添加到可能存在于地球深层上地幔和过渡区的潜在后尖晶石相列表中（例如，Enomoto et al. 2009; Lavina et al. 2011; Lavina and Meng 2015; Woodland et al. 2012，2013，2015; Guignard and Crichton 2014;石井et al. 2014，2015; Myhill et al. 2016; Sinmyo et al. 2016; Uenver-Thiele et al. 2017 a，B）。在许多简单的化学体系中发现了具有M 4 O 5化学计量比的相（O 5-相），包括含有Cr、Al、Fe 3+作为三价阳离子以及Mg和Fe 2+作为二价阳离子的体系（例如，Enomoto等人，2009; Woodland等人，2012，2013;石井等人，2014，2015; Uenver-Thiele等人，2017 a，B）。O 5相常出现在M4 O 5+ M2 O3后尖晶石组合中，如Fe 4 O 5+ Fe 2 O3，FeMgFe 2 O 5+ Fe 2 O3 Fe 2Cr 2 O 5+ Cr2 O3或Fe 2Cr 2 O 5+ Cr2 O3在深部上地幔条件下以尖晶石结构相为代价而变得稳定（Woodland et al. 2012;石井et al. 2014，2015; Uenver-Thiele et al. 2017 a，B）。涉及Fe 4 O 5组分的固溶体特别令人感兴趣，因为同时含有Fe 2+和Fe 3+的能力使其稳定性对氧化还原过程敏感。Woodland等人首次报道了Mg与Fe 4 O 5的结合.（2013）;博法·巴拉兰等人。（2015）随后证明Mg可以完全取代Fe 2+，产生Mg端元Mg 2 Fe 2 O 5。两种端元组成具有相同的空间群Cmcm，具有CaFe 3 O 5型结构（Lavina et al. 2011;博法Ballaran et al. 2015），表明整个Mg-Fe 2+固溶体系列在高压和高温下稳定。Myhill等人（2016）质疑Fe 4 O 5是否可能出现在橄榄岩上地幔或过渡带环境中，因为他们的初步计算表明，其稳定性需要超过预期地幔范围的氧逸度（例如，Frost和McCammon 2008）。然而，这样的结论是基于潜在的相组合，特别是那些富含镁的硅酸盐的不完整的知识。此外，即使这样的情况通常是真实的，这并不排除在局部环境中的O 5-相的稳定性，如那些负责金刚石形成的橄榄石和辉石不共存。实际上，Jacob等人描述的金刚石包裹体中磁铁矿的显微结构是由一种特殊的结构组成的。（2016）导致Uenver-Thiele et al.（2017 b）得出结论，这种磁铁矿在金刚石形成的条件下最初是Fe 4 O 5。
Over the past few years, post-spinel phases have attracted more and more attention due to the discovery of several high-pressure (hp) oxide phases with stoichiometries other than M 3 O 4. Phases with M 4 O 5, M 5 O 6 and M 7 O 9 stoichiometry have now been added to the list of potential post-spinel phases that might be present in the Earth's deep upper mantle and transition zone (eg, Enomoto et al. 2009; Lavina et al. 2011; Lavina and Meng 2015; Woodland et al. 2012, 2013, 2015; Guignard and Crichton 2014; Ishii et al. 2014, 2015; Myhill et al. 2016; Sinmyo et al. 2016; Uenver-Thiele et al. 2017a, b). Phases with an M 4 O 5 stoichiometry (O 5-phase) were found in a number of simple chemical systems, including those containing Cr, Al, Fe 3+ as trivalent cations, and Mg and Fe 2+ as divalent cations (eg, Enomoto et al. 2009; Woodland et al. 2012, 2013; Ishii et al. 2014, 2015; Uenver-Thiele et al. 2017a, b). Often the O 5-phase occurs in an M 4 O 5+ M 2 O 3 post-spinel assemblage, as in the case of Fe 4 O 5+ Fe 2 O 3, FeMgFe 2 O 5+ Fe 2 O 3, Fe 2 Cr 2 O 5+ Cr 2 O 3 or Fe 2 Cr 2 O 5+ Cr 2 O 3 becoming stable at the expense of the spinel-structured phase at conditions of the deep upper mantle (Woodland et al. 2012; Ishii et al. 2014, 2015; Uenver-Thiele et al. 2017a, b).Solid solutions involving the Fe 4 O 5 component are of particular interest because the ability to contain both Fe 2+ and Fe 3+ makes their stability sensitive to redox processes. The incorporation of Mg into Fe 4 O 5 was first reported by Woodland et al.(2013); Boffa Ballaran et al.(2015) subsequently demonstrated that Mg can completely substitute for Fe 2+, producing an Mg endmember, Mg 2 Fe 2 O 5. Both endmember compositions share the same space group Cmcm with a CaFe 3 O 5-type structure (Lavina et al. 2011; Boffa Ballaran et al. 2015), suggesting that the entire Mg-Fe 2+ solid solution series is stable at high pressures and temperatures. Myhill et al.(2016) questioned whether Fe 4 O 5 could occur in a peridotitic upper mantle or transition zone environment since their preliminary calculations implied that its stability required an oxygen fugacity that exceeded the expected mantle range (eg, Frost and McCammon 2008). However, such a conclusion was based upon incomplete knowledge of potential phase assemblages, particularly those with Mg-rich silicates. In addition, even if such a situation were generally true, this does not rule out the stability of an O 5-phase in localized environments, such as those responsible for diamond formation where olivine and pyroxene do not coexist. In fact the microtexture of magnetite in an inclusion in diamond described by Jacob et al.(2016) led Uenver-Thiele et al.(2017b) to conclude that this magnetite was originally Fe 4 O 5 at the conditions of diamond formation.
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DOI：
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发表时间：
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期刊：
影响因子：
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