Stabilities and properties of high-pressure oxide phases containing Cr with focus on solid solutions of (Mg,Fe2+)3Fe2O6 – testing for possible precursor phases for inclusions in diamond

含 Cr 的高压氧化物相的稳定性和性能，重点关注 (Mg,Fe2)3Fe2O6 的固溶体 â 测试金刚石中夹杂物可能的前体相

• 批准号: 504772250
• 负责人: Professor Dr. Alan Butler Woodland
• 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: 2022
• 资助国家: 德国
• 起止时间: 2021-12-31 至 2023-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/504772250?language=en
• 关键词: Stabilities; properties; pressure; oxide; phases

A variety of Fe-oxides with different stoichiometries and crystal structures are now known to be stable at high-pressure conditions corresponding to the lower part of the upper mantle and transition zone. This includes Fe4O5 and Fe5O6, both of which are known to be stable over a wide range in pressure and temperature. Such phases are potential candidates to occur as accessory phases in the mantle assemblage and can be involved in the process of diamond formation. In addition to high-pressure Fe-oxide polymorphs occurring in shocked meteorites, structural investigations of magnetite in an inclusion from a sublithospheric diamond from Orapa point to a precursor phase having been present, possibly with a Fe4O5 or Fe5O6 stoichiometry. Whether Fe5O6 can be considered a viable precursor phase depends its ability to accommodate minor elements like Cr that have been observed in many inclusions in diamonds. However, no information is available on the extent of Cr solid solution in the Fe5O6 structure. It is also unknown if the presence of Cr might help stabilise Mg-rich compositions or even other Mg-rich oxide phases like Mg4Fe2O7, for which only indirect evidence for their stability currently exists.This proposed project aims to experimentally investigating the behavior of Cr in high-pressure Fe-Mg-oxide phases that may be relevant for the Earth’s mantle. The focus will be on the stability of O6-structured phases containing Cr. The project has two major goals: 1) to experimentally determine if the Fe3Cr2O6 and Mg3Cr2O6 end members are stable, and 2) to determine the extent of Cr incorporation in (Mg,Fe2+)3Fe3+2O6. The first part involves a short series of multi-anvil experiments at 14-20 GPa and temperatures of 1300° and 1500°C using pre-synthesised Cr-spinels and oxides as starting materials. Experiments investigating the Mg3Cr2O6 end member will also enable a test of the stability of a potential Mg4Cr2O7 phase, the structure of which is currently unknown. The approach to the second goal will depend on the results from the first part, but will involve experiments using compositions along the Fe2+3Fe3+2O6 – Fe2+3Cr2O6 binary as well as compositions containing Mg. Through knowledge of the systematics of Cr incorporation in the Fe5O6-type structure at high pressures and temperatures we will be able to assess whether the "O6"-phase is a viable candidate to be found as an inclusion or as a potential precursor phase in sublithospheric diamonds. In addition we will be able to provide a crystal chemical characterization of Cr-bearing Fe5O6

现在已知，具有不同化学计量和晶体结构的各种铁氧化物在对应于上地幔下部和过渡带的高压条件下是稳定的。这包括Fe 4 O 5和Fe 5 O 6，已知这两者在宽的压力和温度范围内是稳定的。这些相是地幔组合中可能出现的副相，并可能参与金刚石的形成过程。除了高压铁氧化物的多晶型物发生在冲击陨石，结构调查的磁铁矿夹杂物从岩石圈下的金刚石从Orapa点的前体相已经存在，可能与Fe 4 O 5或Fe 5 O 6的化学计量。Fe 5 O 6是否可以被认为是一种可行的前体相，取决于它容纳微量元素如Cr的能力，这些微量元素在金刚石的许多内含物中已经观察到。然而，没有关于Cr固溶体在Fe 5 O 6结构中的程度的信息。这也是未知的，如果铬的存在可能有助于稳定富镁的组合物，甚至其他富镁的氧化物相，如Mg 4Fe 2 O 7，其中只有间接的证据，他们的稳定性目前存在。重点将是在O 6结构相含铬的稳定性。该项目有两个主要目标：1）通过实验确定Fe 3Cr 2 O 6和Mg3 Cr2 O 6端元是否稳定，以及2）确定Cr掺入（Mg，Fe 2+）3Fe 3 + 2 O 6的程度。第一部分涉及在14-20 GPa和1300° C和1500°C的温度下使用预合成的铬尖晶石和氧化物作为起始材料的一系列短的多砧实验。研究Mg3 Cr2 O 6端元的实验也将能够测试潜在的Mg 4Cr 2 O 7相的稳定性，其结构目前尚不清楚。实现第二个目标的方法将取决于第一部分的结果，但将涉及使用沿着Fe 2 + 3Fe 3 + 2 O 6-Fe 2 + 3Cr 2 O 6二元系的组合物以及含Mg的组合物的实验。通过知识的系统化的Cr掺入在Fe 5 O 6型结构在高压和高温下，我们将能够评估是否“O 6”相是一个可行的候选人被发现作为一个包含物或作为一个潜在的前体相在岩石圈下的钻石。此外，我们将能够提供含铬Fe 5 O 6的晶体化学表征