Understanding the interaction between fluids and the depleted peridotite is essential in deciphering the geochemical and mineralogical variability of the sub-continental lithospheric mantle (SCLM). High-density fluid (HDF) inclusions trapped in diamonds during their formation in the SCLM are potential metasomatic agents. In this study, experiments were performed on a harzburgite + silicic fluid system at an 80:20 rock:fluid ratio (bulk 5 wt% H₂O and 3 wt% CO₂), simulating the infiltration of a slab-derived silicic fluid into the SCLM. Experiments were performed at 3–6 GPa and 900–1200 °C on a rocking multi-anvil apparatus, conditions corresponding to the deep SCLM. The fluid and melt compositions were directly determined using the cryogenic LA-ICP-MS technique. The metasomatized peridotite consisted of olivine, clinopyroxene, phlogopite, orthopyroxene, amphibole, and magnesite. The H₂O-CO₂-saturated solidus in this system is located between 900–1000 °C at 3 GPa and between 1000–1100 °C at 4–6 GPa. The fluids at all pressures are alkali-rich. With increasing temperature and crossing the solidus, the melts evolve towards the initial silicic fluid composition.

Together with previous studies on various peridotite + H₂O ± CO₂ systems, the results presented here suggest a positive correlation between the bulk alkali/volatile ratio and the solidus temperatures. An increase in this parameter and in the mantle fertility (i.e., Ca#) increases the near-solidus isobaric melt production rate. The experimental fluid compositions found in this study are similar to saline HDFs. We propose a scenario where the percolation of a slab-derived silicic fluid into the depleted cratonic peridotite leads to the formation of near-solidus saline fluids. Such sequence of metasomatic events was reported from fluid inclusions in diamonds from several localities in the Kaapvaal craton in South Africa (e.g., De Beers, Finsch, Voorspoed).

了解流体与贫化橄榄岩之间的相互作用对于解读次大陆岩石圈地幔 (SCLM) 的地球化学和矿物学变异性至关重要。在 SCLM 中形成过程中被困在钻石中的高密度流体 (HDF) 内含物是潜在的交代物质。在本研究中，实验是在 80:20 的岩石：流体比（散装 5 wt% H ₂ O 和 3 wt% CO ₂)，模拟板片衍生的硅流体渗入 SCLM。实验是在 3-6 GPa 和 900-1200°C 的摇摆多砧装置上进行的，条件对应于深 SCLM。使用低温 LA-ICP-MS 技术直接测定流体和熔体成分。交代橄榄岩由橄榄石、单斜辉石、金云母、斜方辉石、闪石和菱镁矿组成。该系统中的 H ₂ O-CO ₂饱和固相线在 3 GPa 时位于 900–1000 °C 之间，在 4–6 GPa 时位于 1000–1100 °C 之间。所有压力下的流体都富含碱。随着温度升高和穿过固相线，熔体向初始硅流体组成演变。

连同先前对各种橄榄岩 + H ₂ O ± CO ₂系统的研究，这里提出的结果表明本体碱/挥发比与固相线温度之间存在正相关。该参数和地幔肥力（即Ca#）的增加会增加近固相线等压熔体的产率。本研究中发现的实验流体成分类似于盐水 HDF。我们提出了一种方案，其中板片衍生的硅质流体渗入贫化的克拉通橄榄岩中导致近固相盐流体的形成。据报道，这种交代事件序列来自南非 Kaapvaal 克拉通几个地方（例如，De Beers、Finsch、Voorspoed）的钻石中的流体包裹体。