Discovery of a hexagonal ultradense hydrous phase in (Fe,Al)OOH
Discovery of a hexagonal ultradense hydrous phase in (Fe,Al)OOH
复制标题
DOI：
10.1073/pnas.1720510115
复制
发表时间：
2018-03
期刊：
影响因子：
--
通讯作者：
Li Zhang;Hongsheng Yuan;Y. Meng;H. Mao
中科院分区：
文献类型：
--
作者：
Li Zhang;Hongsheng Yuan;Y. Meng;H. Mao
下地幔可能是我们星球上最大的水库，这在很大程度上取决于含水矿物的可用性，这些矿物可以储存和运输水到下地幔深处。在实验上，在与地球深部相对应的高压-高温条件下，在多相体系中识别未知的水相是一个巨大的挑战。我们结合粉末x射线衍射和多晶粒指数化发现（Fe,Al）OOH在107-136 GPa和2400 K下存在六方水相。数十个单独的晶体，每个都有其独特的取向矩阵，证实了六方相的存在。这项研究突出了水储存的候选物。深下地幔（DLM）水库依赖于含水矿物的可用性，这些矿物可以在不脱水的情况下将水储存和输送到DLM。最近发现了具有cacl2型结构的AlOOH （Z = 2）和具有立方黄铁矿型结构的FeOOH （Z = 4）的水相在DLM的高压-高温（P-T）条件下稳定存在。我们在107-136 GPa和2400 K下的实验进一步证明了（Fe,Al）OOH在六边形晶格中是稳定的。结合粉末x射线衍射技术和多晶指数法，我们可以在110 GPa下确定a = 10.5803(6) Å和c = 2.5897(3) Å的六方水相。六方（Fe,Al）OOH在低温度下可在相同密度下转变为立方黄铁矿结构。δ-AlOOH与水与Fe反应生成的FeOOH结合形成六方相，可在DLM中储存大量的水。
Significance The lower mantle is potentially the most massive water reservoir in our planet, which largely depends on availability of hydrous minerals which can store and transport water down to the deep lower mantle. Experimentally, it is a great challenge to identify an unknown hydrous phase in a multiphase system under high-pressure–temperature conditions corresponding to the deep Earth. We combined powder X-ray diffraction and multigrain indexation to discover a hexagonal hydrous phase in (Fe,Al)OOH at 107–136 GPa and 2,400 K. Tens of individual crystallites, each with its unique orientation matrix, confirm the existence of the hexagonal phase. This study highlights a candidate for water storage. A deep lower-mantle (DLM) water reservoir depends on availability of hydrous minerals which can store and transport water into the DLM without dehydration. Recent discoveries found hydrous phases AlOOH (Z = 2) with a CaCl2-type structure and FeOOH (Z = 4) with a cubic pyrite-type structure stable under the high-pressure–temperature (P-T) conditions of the DLM. Our experiments at 107–136 GPa and 2,400 K have further demonstrated that (Fe,Al)OOH is stabilized in a hexagonal lattice. By combining powder X-ray-diffraction techniques with multigrain indexation, we are able to determine this hexagonal hydrous phase with a = 10.5803(6) Å and c = 2.5897(3) Å at 110 GPa. Hexagonal (Fe,Al)OOH can transform to the cubic pyrite structure at low T with the same density. The hexagonal phase can be formed when δ-AlOOH incorporates FeOOH produced by reaction between water and Fe, which may store a substantial quantity of water in the DLM.