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Generation of some kimberlite magmas is realized as the process of partial melting of peridotite, in which the CO 2 and H 2 O fugacity is controlled by carbonates and hydrous phases (phlogopite, amphibole) at least at the initial stage [1]. Amphibole and mica are stable and the most abundant hydrous phases in the metaso matized mantle [2]. Their genesis is traditionally interpreted by the influence of hydrous fluids on man tle peridotite.The geochemical data show that the stage of kim berlite magma generation was preceded by intrusion of carbonatite melts into the protolith [3]. According to the data of the study of microinclusions in diamonds, the composition of such melts varied from ultra alka line carbonate to silicate-carbonate [4]. The finds of phlogopite inclusions in diamonds in association with the ultrabasic and eclogitic minerals [5] provide clear evidence for the stability of phlogopite in the dia mond forming medium.Experimental data do not provide unambiguous evidence for the stability of phlogopite in peridotite of the subcratonic lithosphere in the presence of carbon atite melts. It is shown in [6] that phlogopite is not sta ble in the system modeling kimberlite of group II at a pressure of >4 GPa at the expense of the reaction 2Phl + MgCO 2 → 2Opx + Ol + Grt + K 2 CO 3 (L) + 2H 2 O (L). On the other hand, study of the phlogopite-magnesite system at 4-8 GPa showed that the associations con taining phlogopite and magnesite could be stable at a thermal regime of the subcontinental lithosphere up tõ 6 GPa [7]. In this paper, we report the results of the experi mental study of the conditions of phlogopite crystalli zation upon interaction of a K rich hydrous carbonate melt (an assumed metasomatic agent) with a mineral association modeling mantle lherzolite and harzburg ite. Experiments were performed at 5.5 GPa and 1200°C, i.e., in the conditions typical of the lowermost subcratonic lithosphere. The duration of experiments (150 h) provided the formation of equilibrium associ ations. The data obtained allowed us to estimate the conditions of phlogopite stability/generation upon the interaction of peridotite with the hydrous carbonatite melt and to determine the composition of the melt in equilibrium with phlogopite bearing associations under the conditions of the subcratonic lithosphere.The composition of the melt formed at the expense of carbonated pelite melting at 8 GPa and 1100°С (hereinafter, GS) [8] was applied as an ultra alkaline carbonatite agent, which may be potentially formed in the subduction zones. The asthenospheric carbonate melts were modeled by the composition of the melt formed at the expense of melting of the K rich car bonated harzburgite at 10 GPa and 1400°С (B10) and at 6 GPa and 1400°С (B6) [9]. The composition HZ86[10] was used as garnet lherzolite (hereinafter, LC); the composition HC (without addition of K 2 CO 3 ) [9] was used as garnet harzburgite. The composition LC in the test experiment at 5.5 GPa and 1200°С generated lherzolite contained (wt %) Ol (52), Opx (19), Cpx (1...