It is well known that water significantly lowers mantle solidi. But it turns out this paradigm is not always true. Here, we studied the interaction of K-rich carbonate melts with the natural garnet lherzolite from the Udachnaya kimberlite (Russia) in the presence of water at 3.0–6.5 GPa, corresponding to depths of 100–200 km. We found that at ≤ 1100 °C, the metasomatic interaction consumes garnet, orthopyroxene, and melt to produce phlogopite ± K-richterite + magnesite ± dolomite. Besides, primary clinopyroxene is replaced by one with a lower amount of jadeite component. Thus, the addition of water to the K-rich carbonate melt, infiltrating the subcontinental lithospheric mantle, should yield its partial or complete disappearance accompanied by phlogopitization and carbonation.

The studied systems have H₂O/K₂O = 2, like that in phlogopite, and therefore correspond to carbonated phlogopite peridotite under fluid-absent conditions. At 4.0–6.5 GPa, the solidus of carbonated phlogopite peridotite is controlled by the following reaction: phlogopite + clinopyroxene + magnesite = garnet + orthopyroxene + olivine + hydrous K-carbonatite melt, which is bracketed between 1100 and 1200 °C. At 3 GPa, the solidus temperature decreases to about 1050 °C presumably owing to the Ca-Mg exchange reaction, clinopyroxene + magnesite = orthopyroxene + dolomite, which stabilizes dolomite reacting with phlogopite at a lower temperature than magnesite.

Our results suggest that the phlogopite- and carbonate-rich metasomatic vein networks, weakening rigid lithosphere and promoting continental rifting, could be formed as a result of infiltration of hydrous K-carbonatite melt at the base of subcontinental lithospheric mantle. Stretching and thinning of the cratonic lithosphere make geotherms warmer and shifts their intersections with the solidus of carbonated phlogopite peridotite to shallower depths. Consequently, the successive erosion of the continental lithosphere and ascent of the lithosphere-asthenosphere boundary during continental rifting should be accompanied by remelting of phlogopite-carbonate metasomes, upward percolation of K-rich melt, and its solidification at the front of the magmatic-metasomatic mantle system.

众所周知，水会显着降低地幔固体。但事实证明，这种范式并不总是正确的。在这里，我们研究了富含钾的碳酸盐熔体与来自 Udachnaya 金伯利岩（俄罗斯）的天然石榴石二辉长岩在 3.0-6.5 GPa 的水存在下的相互作用，对应于 100-200 公里的深度。我们发现在 ≤ 1100 °C 时，交代相互作用消耗石榴石、斜方辉石和熔体，产生金云母 ± K-富锂辉石 + 菱镁矿 ± 白云石。此外，初级单斜辉石被一种翡翠成分较少的辉石所取代。因此，向富含钾的碳酸盐熔体中加入水，渗入次大陆岩石圈地幔，会导致其部分或完全消失，伴随着金云母化和碳酸盐化。

研究的系统具有 H ₂ O/K ₂ O = 2，就像金云母中的那样，因此对应于无流体条件下的碳酸化金云母橄榄岩。在 4.0–6.5 GPa 下，碳酸化金云母橄榄岩的固相线受以下反应控制：金云母 + 斜辉石 + 菱镁矿 = 石榴石 + 斜方辉石 + 橄榄石 + 含水碳酸钾熔体，其温度介于 1100 至 1200 °C 之间。在 3 GPa 时，固相线温度下降到约 1050 °C，这大概是由于 Ca-Mg 交换反应，单斜辉石 + 菱镁矿 = 斜辉石 + 白云石，这使白云石与金云母反应的温度比菱镁矿低。

我们的研究结果表明，富含金云母和碳酸盐的交代脉网络，削弱了刚性岩石圈并促进了大陆裂谷，可能是含水碳酸钾熔体在次大陆岩石圈地幔底部渗透的结果。克拉通岩石圈的拉伸和变薄使地温变暖，并将它们与碳化金云母橄榄岩固相线的交点转移到更浅的深度。因此，在大陆裂谷期间，大陆岩石圈的连续侵蚀和岩石圈-软流圈边界的上升应该伴随着金云母-碳酸盐交代体的重熔、富钾熔体的向上渗流及其在岩浆-交代前缘的凝固。地幔系统。