研究人员报道了在幔源金刚石中观察到的作为包裹体的硅镁石族的羟基成分。在巴西的一颗金刚石中发现与橄榄石、镁铬铁矿、含镁方解石、白云石、石英、云母，和一种蛇纹石类矿物共生的含水粒硅镁石和含水斜硅镁石。
橄榄石为高镁橄榄石(Mg#97)，具有非地幔氧同位素组成(δ18O+6.2‰)，与流体包裹体和含水矿物有关，其特征可能继承自蛇纹岩原岩。研究结果构成了下克拉通地幔龙骨中存在脱镁橄榄岩原岩的直接证据，对地幔中含水相的稳定性和金刚石形成流体的来源提出了重要的限制。
据悉，地球上地幔中的水是决定地幔性质(如强度和熔融行为)的一个次要但至关重要的组成部分。含有元素量水的矿物，如硅美石族矿物，是上地幔中重要但特征不明确的挥发物潜在储集层。
附：英文原文
Title: Dense hydrated in Mg-silicates diamond: Implications for transport of H2O into the mantle
Author: Luísa D. V. Carvalho, Thomas Stachel, Robert W. Luth, Andrew J. Locock, D. Graham Pearson, Matthew Steele-MacInnis, Richard A. Stern, Fabrizio Nestola, Ricardo Scholz, Tiago Jalowitzki, Reinhardt A. Fuck
Issue&Volume: 2024-03-15
Abstract: Water in Earth’s upper mantle is a minor and yet critically important component that dictates mantle properties such as strength and melting behavior. Minerals with stoichiometric water, such as those of the humite group, are important yet poorly characterized potential reservoirs for volatiles in the upper mantle. Here, we report observation of hydroxyl members of the humite group as inclusions in mantle-derived diamond. Hydroxylchondrodite and hydroxylclinohumite were found coexisting with olivine, magnesiochromite, Mg-bearing calcite, dolomite, quartz, mica, and a djerfisherite-group mineral in a diamond from Brazil. The olivine is highly forsteritic (Mg#97), with non–mantle-like oxygen isotope composition (δ18O+6.2‰), and is associated with fluid inclusions and hydrous minerals—features that could be inherited from a serpentinite protolith. Our results constitute direct evidence for the presence of deserpentinized peridotitic protoliths in subcratonic mantle keels, placing important constraints on the stability of hydrous phases in the mantle and the origin of diamond-forming fluids.
DOI: adl4306
Source: https://www.science.org/doi/10.1126/sciadv.adl4306