Water solubility in the dominant lower-mantle bridgmanite phase remains controversial. Discrepancies between previous results highlight the importance of the growth high-quality single crystals of bridgmanite under high-pressure and high-temperature conditions corresponding to the top of the lower mantle. Here we synthesized high-quality single crystals of aluminous bridgmanite up to 300 μm in size that were saturated with hydrous melt at 24–26 GPa and 1700–1900 K using both stoichiometric and MgO-rich non-stoichiometric hydrous starting materials in a multi-anvil press. Fourier-transform infrared spectroscopy measurements on clear and pure spots of the single-crystal bridgmanites did not detect any pronounced OH-stretching bands, which were prominent in some earlier studies. The present results support that the lower-mantle dominated bridgmanite is nearly dry, at least at the top of the lower mantle, and that Al³⁺ and Fe³⁺ cannot enhance water incorporation into the crystal structure even in the presence of oxygen vacancies. Large partition coefficients of water between transition-zone minerals and dry lower-mantle dominated bridgmanite further support dehydration melting at the top of the lower mantle. We suggest that the majority of the top of a pyrolitic lower mantle is nearly dry based on the dry principal minerals and stability of hydrous phases in this region.

在主要的下地幔布里奇曼石相中的水溶性仍然存在争议。先前结果之间的差异突出了在对应于下地幔顶部的高压和高温条件下生长高质量布里奇曼石单晶的重要性。在这里，我们使用化学计量和富含 MgO 的非化学计量含水起始材料合成了尺寸高达 300 μm 的高质量铝桥锰单晶，这些单晶在 24-26 GPa 和 1700-1900 K 下被含水熔体饱和。铁砧压榨机。傅立叶变换红外光谱对单晶桥锰矿的清晰和纯点的测量没有检测到任何明显的 OH 拉伸带，这在一些早期的研究中很突出。即使存在氧空位，³⁺和Fe ³⁺也不能增强水结合到晶体结构中。过渡带矿物和干燥的下地幔主导的布里格曼岩之间的水分配系数大，进一步支持下地幔顶部的脱水熔融。根据该地区干燥的主要矿物和水相的稳定性，我们认为热解岩下地幔的大部分顶部几乎是干燥的。