水在地球深部下地幔中的后钙钛矿（post-perovskite, PPv）和布里奇曼石（bridgmanite, Bdg）中的高溶解度
High solubility of water in post-perovskite and bridgmanite in the Earth's deep lower mantle
AI总结：
本研究通过熔融实验结合Cryo-SIMS测量，发现水在深部下地幔的Bdg和PPv中溶解度极高，表明俯冲板块到地幔底部不释放水，提出富水矿物可能构成深部地幔的低D/H水储层。
AI中文摘要：
地球地幔中的水会引发熔融，产生强烈的化学异质性，并改变其流变学和传输性质，这些是理解地震波速异常、对流运动和电导率的关键。然而，水的丰度及其在深部地幔中的作用仍不确定且存在争议，尤其是在核幔边界（CMB）区域的条件下。本研究针对含水的天然地幔成分（包含H₂O和D₂O），在地球整个下地幔压力范围内开展熔融实验，实验中熔体与布里奇曼石（Bdg）和/或后钙钛矿（PPv）共存，这两种矿物分别是下地幔和最底部地幔的主要成分。高分辨率二次离子质谱（Cryo-SIMS）测量显示，Bdg中的水浓度高达5500重量ppm，PPv中的水浓度高达1.22重量%，且相对于共存熔体，氘/氢（D/H）存在强烈富集。水在CMB条件下于Bdg和PPv中的高溶解度表明，俯冲板块到达地幔底部时不会释放水，该过程无法解释最底部地幔和最顶部外核中推断出的强烈化学异质性，也无法解释地震高速区域的超低速带（ULVZ）状结构。富水的Bdg和PPv可能存在于大型低速剪切省和ULVZ中，这些区域可能是原始岩浆洋的残余，预计会拥有源自早期地球的深部低D/H水储层，该储层偶尔会被最底部地幔来源的地幔柱采样。
英文摘要：
Water in the Earth's mantle induces melting, giving rise to strong chemical heterogeneity, and alters its rheological and transport properties, which are keys to understanding seismic-wave speeds anomalies, convective motions and electrical conductivity. However, the abundance of water and its role in the deep mantle remain uncertain and controversial, particularly at conditions of the core-mantle boundary (CMB) region. Here we carry out melting experiments on a hydrous, natural mantle composition including both $H_2O$ and $D_2O$ over the entire pressure range of the Earth's lower mantle, in which melt coexists with bridgmanite (Bdg) and/or post-perovskite (PPv), the primary constituents of the respective lower and lowermost mantle. High-resolution secondary-ion mass spectroscopy (Cryo-SIMS) measurements reveal high water concentrations in Bdg (up to 5,500 ppm by weight) and PPv (up to 1.22 wt%) with strong enrichment in deuterium/hydrogen (D/H) relative to coexisting melt. The high solubilities of water in Bdg and PPv at CMB conditions suggest that subducting slabs do not release water when they reach the bottom of the mantle, and such a process cannot account for strong chemical heterogeneities inferred in the lowermost mantle and the topmost outer core, nor for ultralow-velocity zone (ULVZ)-like structures in seismically fast regions. Water-rich Bdg and PPv may be present in the large low shear velocity provinces and ULVZs, which may be the residue of a basal magma ocean and are predicted to host a deep low D/H water reservoir inherited from the early Earth that is occasionally sampled by plumes of a lowermost-mantle origin.
