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Stabilities and properties of Mg, Al and Cr-bearing solid solutions of newly discovered Fe3+-Fe2+ oxides at transition zone conditions: approaching geologically relevant compositions

新发现的 Fe3 -Fe2 氧化物在过渡区条件下的含 Mg、Al 和 Cr 固溶体的稳定性和性能：接近地质相关成分

基本信息

批准号：
232955929
负责人：
Dr. Tiziana Boffa Ballaran
金额：
--
依托单位：
Bayerisches Forschungsinstitut für Experimentelle Geochemie und Geophysik (BGI)
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2013
资助国家：
德国
起止时间：
2012-12-31 至 2022-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/232955929?language=en
关键词：
Stabilities properties Mg Al Cr

项目摘要

Spinel-structured phases with AB2O4 stoichiometry are common in the Earth and can have a variety of compositions. For example, (Mg,Fe)2SiO4 ringwoodite is a dominant phase in the lower half of the Earths transition zone. Si-free oxides such as magnetite (FeFe2O4) and magnesioferrite (MgFe2O4) also occur as inclusions in diamond, including those considered as having a super deep origin in the transition zone or even lower mantle. Thus, the phase relations of such oxides are important for interpreting such occurrences, especially when textural evidence suggests that they formed from a precursor phase that has subsequently transformed. Shocked meteorites may also preserve evidence for post-spinel phases that formed at high pressures. The stability of post-spinel assemblages of MgFe2O4 was the subject of a previous study that illustrated how such information can constrain the interpretation of natural samples. This project is an extension of the preceding project where we aim to investigate the phase relations of more complex compositions that approach those encountered in nature. One primary goal is to determine the effect that Al and Cr have on the phase relations of Fe-Mg oxides in the post-spinel range of P and T. Under these conditions, assemblages containing solid solutions of Fe4O5, Fe5O6 or hp-Fe3O4-type phases are expected. Based upon previous experience, oxide phases with other stoichiometries may also be encountered (i.e. Mg3Fe4O9). These phases will be characterised and their assemblages integrated into phase diagrams applicable to the conditions of the deep upper mantle and transition zone. We will further focus on the solid solution behavior of Mg, Al and Cr in Fe5O6, since very little is known about this phase and preliminary thermodynamic calculations suggest its redox stability makes it a more likely candidate phase for the expected conditions in the Earths deep mantle than Fe4O5. Its potential stability with mantle silicates will also be tested. In order to develop thermodynamic models for the O5 and O6 phases, their compression behavior will be investigated

具有 AB2O4 化学计量的尖晶石结构相在地球中很常见，并且可以具有多种成分。例如，(Mg,Fe)2SiO4 尖晶石是地球过渡带下半部的主要相。无硅氧化物，如磁铁矿 (FeFe2O4) 和镁铁氧体 (MgFe2O4) 也以包裹体形式出现在金刚石中，包括那些被认为具有超深起源于过渡带甚至下地幔的氧化物。因此，此类氧化物的相关系对于解释此类事件非常重要，特别是当结构证据表明它们是由随后发生转变的前体相形成时。震惊的陨石还可能保留高压下形成的后尖晶石相的证据。 MgFe2O4 后尖晶石组合的稳定性是先前研究的主题，该研究说明了此类信息如何限制对天然样品的解释。该项目是前一个项目的延伸，我们的目标是研究接近自然界中遇到的更复杂成分的相位关系。一个主要目标是确定 Al 和 Cr 对尖晶石后 P 和 T 范围内 Fe-Mg 氧化物相关系的影响。在这些条件下，预计会出现含有 Fe4O5、Fe5O6 或 hp-Fe3O4 型相固溶体的组合体。根据以前的经验，也可能会遇到具有其他化学计量的氧化物相（即 Mg3Fe4O9）。这些相将被表征，并将它们的组合整合到适用于深部上地幔和过渡带条件的相图中。我们将进一步关注 Mg、Al 和 Cr 在 Fe5O6 中的固溶行为，因为人们对这一相知之甚少，初步的热力学计算表明，其氧化还原稳定性使其比 Fe4O5 更有可能成为地球深部地幔预期条件的候选相。其与地幔硅酸盐的潜在稳定性也将得到测试。为了开发 O5 和 O6 相的热力学模型，将研究它们的压缩行为