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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AB 2 O 4化学计量比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）2SiO 4林伍德石是地球过渡带下半部分的主要相。不含硅的氧化物，如磁铁矿（FeFe 2 O 4）和镁铁氧体（MgFe 2 O 4）也作为包裹体出现在金刚石中，包括那些被认为在过渡带甚至下地幔中具有超深起源的包裹体。因此，这种氧化物的相关系是重要的解释这种情况下，特别是当纹理证据表明，他们形成的前体相，随后转化。冲击陨石也可能保存在高压下形成的后尖晶石相的证据。后尖晶石组合的MgFe 2 O 4的稳定性是以前的一项研究的主题，该研究说明了这些信息如何限制对天然样品的解释。这个项目是前一个项目的延伸，我们的目标是研究更复杂的组合物，接近那些在自然界中遇到的相位关系。一个主要目标是确定Al和Cr对P和T的后尖晶石范围内的Fe-Mg氧化物的相关系的影响。在这些条件下，组合物包含Fe 4 O 5，Fe 5 O 6或hp-Fe 3 O 4型相的固溶体。根据以前的经验，也可能遇到其他化学计量的氧化物相（即Mg3 Fe 4 O 9）。将对这些相进行表征，并将其组合整合到适用于上地幔深处和过渡区条件的相图中。我们将进一步关注Mg，Al和Cr在Fe 5 O 6中的固溶体行为，因为对该相知之甚少，初步热力学计算表明其氧化还原稳定性使其比Fe 4 O 5更可能成为地球深部地幔预期条件的候选相。还将测试其与地幔硅酸盐的潜在稳定性。为了建立O 5和O 6相的热力学模型，将研究它们的压缩行为