超高压高温下三价铁和铝对布里奇曼石的化学缺陷和物理性质的影响

Although bridgmanite (Brg) mainly consist of Si4+, Mg2+ and Fe2+, it also contains trivalent cations, Al3+ and Fe3+. Al3+ is contained as the AlAlO3 (charged-coupled, CC) and MgAlO2.5 (oxygen vacancy, OV) components. Fe3+ could be contained similarly as FeFeO3 (CC) and MgFeO2.5 (OV). When both Fe3+ and Al3+ are contained, FeAlO3 forms even at a reduced enviroment. Among these components, the OV component should have special significance in geoscience because the presence of OV will enhance creep, and therefore decrease lower-mantle viscosity. Moreover, OV in bridgmanite may transport volatiles such as H2O and noble gas (Ar，He and Xe) into the lower mantle. Hence, the OV and CC contents in bridgmanite under given conditions are vital for understanding dynamics and geochemical cycling in the lower mantle. For these reasons, we investigated the effect of Al3+ and Fe3+ on the chemistry defect of bridgmanite under lower-mantle conditions. Here, we will develop ultrahigh-pressure and high temperature technique in a large volume press to investigate the stability and solubility of the FeAlO3 component in bridgmanite and ternary phase relations in the system MgO-FeAlO3-SiO2。Finally, we will discuss the chemistry and thermoelastic properties of bridgmanite and implication for the FeAlO3 component， slab stagnation and volatiles storage in the lower mantle.

下地幔一直是地球内部最复杂的区域之一，其物理结构和化学组成一直存在科学争议。布里奇曼石，此区域最主要的矿物，可以储存大量的Al3+和Fe3+。Al3+和Fe3+的掺杂不仅可以显著改变布里奇曼石的物理和化学性质，而且可以创造氧缺位的化学缺陷，从而可以引入挥发性成分（惰性气体和水）到下地幔中。本项目将发展和利用大腔体压机的超高压高温实验技术，通过调控初始物的Mg/Si比值、Al3+和Fe3+含量以及合成的氧化还原环境，获得可以达到化学平衡的毫米级别的布里奇曼石，研究Al3+和Fe3+的掺杂对布里奇曼石的氧缺位和密度的影响，探索布里奇曼石中的FeAlO3含量，建立MgSiO3-FeAlO3体系的布里奇曼石的热力学计算模型和下地幔温压条件下的MgO-FeAlO3-SiO2体系的三相图。从而帮助了解下地幔的物质组成和储存挥发性成分的能力，同时为下地幔中部观测到的俯冲带的滞留提供新的解释角度。

布里奇曼石是下地幔最主要的矿物，可以储存大量的Al3+和Fe3+，其化学性质的研究可以帮助了解地球下地幔的物质组成和性质。通过本项目的资助，开发了国产碳化钨压砧组装体，发展了商用大腔体压机的超高压高温实验技术，在室温和高温下，毫米级样品仓均超过35GPa;利用硼掺杂金刚石加热器将温度产生进一步达到4300K以上；通过调控初始物的Mg/Si比值、Al3+和Fe3+含量以及合成氧化还原环境，在27GPa和1700-2000K进行了系列高温高压实验，获得了与刚玉、三氧化二铁、方镁石或者富Al/Fe相共存的布里奇曼石，发现Al3+和Fe3+主要以电荷耦合替代形式FeAlO3存在布里奇曼石中，其FeAlO3最大固溶量大约在67mol%，发现Al3+和Fe3+的掺杂可以降低布里奇曼石的氧缺位含量，增加其摩尔体积；进一步建立了下地幔顶部温压条件下的MgO-FeAlO3-SiO2体系的三相图，阐明了在地幔模型pyrolite和玄武岩MORB 中FeAlO3成分的含量的差异性；本项目的研究有助于了解下地幔最主要矿物布里奇曼石的物理和化学性质，进一步帮助了解下地幔的物质组成和性质。