Static compression of hydrous silicate melt and the effect of water on planetary differentiation

High pressure experiments using the sink/float method have bracketed the density of hydrous iron-rich ultrabasic silicate melt from 1.35 to 10.0 GPa at temperatures from 1400 to 1860 °C. The silicate melt composition was a 50–50 mixture of natural komatiite and synthetic fayalite. Water was added in the form of brucite Mg(OH)₂ and was present in the experimental run products at 2 wt.% and 5 wt.% levels as confirmed by microprobe analyses of total oxygen. Buoyancy marker spheres were olivines and garnets of known composition and density. The density of the silicate melt with 5 wt.% water at 2 GPa and 1500 °C is 0.192 g cm^? 3 less than the anhydrous form of this melt at the same P and T. This density difference gives a partial molar volume of water in silicate melt of ～ 7 cm³ mol^? 1, which is similar to previous studies at high pressure. The komatiite–fayalite liquids with 0 and 2 wt.% H₂O, have extrapolated density crossovers with equilibrium liquidus olivine at 8 and 9 GPa respectively, but there is no crossover for the liquid with 5 wt.% H₂O. These results are consistent with the hypothesis that dense hydrous melts could be gravitationally stable atop the 410 km discontinuity in the Earth. The results also support the notion that equilibrium liquidus olivine could float in an FeO-rich hydrous martian magma ocean. Extrapolation of the data suggests that FeO-rich hydrous melt could be negatively buoyant in the Earth's D″-region or atop the core–mantle-boundary (CMB), although experiments at higher pressure are needed to confirm this prediction.     

Fragmentation in kimberlite: products and intensity of explosive eruption

The explosive eruption of kimberlite magma is capable of producing a variety of pyroclast sizes, shapes, and textures. However, all pyroclastic deposits of kimberlite comprise two main types of pyroclasts: (1) pyroclasts of kimberlite with or without enclosed olivine crystals and (2) olivine crystals which lack coatings of kimberlite. Here, we propose two hypotheses for how kimberlite magmas are modified due to explosive eruption: (1) olivine crystals break during kimberlite eruption, and (2) kimberlite melt can be efficiently separated from crystals during eruption. These ideas are tested against data collected from field study and image analysis of coherent kimberlite and fragmental kimberlite from kimberlite pipes at Diavik, NT. Olivines are expected to break because of rapid pressure changes during the explosive eruption. Disruption of kimberlite magma, and pyroclast production, is driven by ductile deformation processes, rather than by brittle fragmentation. The extent to which melt separates from olivine crystals to produce kimberlite-free crystals is a direct consequence of the relative proportions of gas, melt and crystals. Lastly, the properties of juvenile pyroclasts in deposits of pyroclastic kimberlite are used to index the relative intensity of kimberlite eruptions. A fragmentation index is proposed for kimberlite eruption based on: (a) crystal size distributions of olivine and on (b) ratios of selvage-free olivine pyroclasts to pyroclasts of kimberlite with or without olivine crystals.     

Experimental investigation of phase transformations of olivine and enstatite at the lower part of the mantle transition zone: Implications for structure of the 660 km seismic discontinuity

High-pressure polymorphs of olivine and enstatite are major constituent minerals in the mantle transition zone(MTZ).The phase transformations of olivine and enstatite at pressure and temperature conditions corresponding to the lower part of the MTZ are import for understanding the nature of the 660 km seismic discontinuity.In this study,we determine phase transformations of olivine(MgSi2O4) and enstatite(MgSiO3) systematiclly at pressures between 21.3 and 24.4 GPa and at a constant temperature of 1600℃.The most profound discrepancy between olivine and enstatite phase transformation is the occurency of perovskite.In the olivine system,the post-spinel transformation occures at 23.8 GPa,corresponding to a depth of 660 km.In contrast,perovskite appears at 23 GPa(640 km) in the enstatite system.The ~1 GPa gap could explain the uplifting and/or splitting of the 660 km seismic discountinuity under eastern China.     

高温高压下碳酸盐熔体对地幔岩电导率的影响

为了观测含碳酸盐地幔岩部分熔融过程中电导率的变化,厘清碳酸盐熔体在金伯利岩岩浆形成过程中所起的作用,并探讨Slave克拉通中部Lac de Gras地区约80～120km深处的高导成因,我们利用DS 3600t六面顶压机和Solartron 1260阻抗/增益-相位分析仪在1.0～3.0GPa、673～1873K温压条件下分别测量了含碳酸钠(Na_2CO_3)、碳酸钙(CaCO_3)和大洋中脊玄武岩(MORB)的地幔岩样品的电导率.实验结果表明,地幔岩样品的电导率主要受到温度和组分的影响,而压力对其影响较小.在温度低于1023K时,含Na_2CO_3地幔岩样品的电导率明显高于含同比重CaCO_3和MORB的;温度达到1023K时,含Na_2CO_3地幔岩样品开始熔融;但在之后的200K温度区间内,该部分熔融样品的电导率随温度的增加几乎不发生变化.这一现象或许揭示:地幔深部的碳酸质岩浆在快速上升过程中会同化吸收岩石圈地幔中的斜方辉石(Opx),进而形成金伯利岩岩浆,期间岩浆的电导率几乎不发生变化.含CaCO_3和MORB的地幔岩样品分别在1723K和1423K开始熔融,其部分熔融样品的电导率随温度的增加而快速增加.依据前人的研究结果和我们的实验结果,我们认为可以用含碳酸盐的部分熔融样品来解释Slave克拉通中部Lac de Gras地区约80～120km深处的异常高导现象,并推测熔体中碳酸盐的熔体比例小于2wt.%.     

Reaction experiments between tonalitic melt and mantle olivine and their implications for genesis of high-Mg andesites within cratons

High-Mg (Mg#>45) andesites (HMA) within cratons attract great attention from geologists. Their origin remains strongly debated. In order to examine and provide direct evidence for previous assumptions about HMA’s genesis inferred from petrological and geochemical investigations, we performed reaction experiments between tonalitic melt and mantle olivine on a six-anvil apparatus at high-temperature of 1250–1400°C and high-pressure of 2.0–5.0 GPa. Our experiments in this work simulated the interaction between the tonalitic melt derived from partial melting of eclogitized lower crust foundering into the Earth’s mantle and mantle peridotite. The experimental results show that the reacted melts have very similar variations in chemical compositions to the HMAs within the North China Craton. Therefore, this interaction is probably an important process to generate the HMAs within crations.     

Closure of the Fe-S-Si liquid miscibility gap at high pressure

A high pressure investigation of melting relationships in the Fe-S-Si system has been conducted in a multi-anvil apparatus from 10 to 27 GPa and up to 2343 K. At 1 atm, the Fe-S-Si ternary system exhibits a vast miscibility gap [Raghavan, V., 1988. Phase diagrams of ternary iron alloys. Part 2: Ternary systems containing iron and sulphur. Indian Institute of Metals, Calcutta]. Quenched samples from experiments conducted at 10 and 12 GPa show an emulsion of immiscible liquids (an Fe-S melt and an Fe-Si melt). The liquid miscibility gap persists to at least 2343 K at 10 GPa. At 15 GPa, only one liquid is quenched, with a fine homogeneous dendritic texture. The results provide a mechanism to incorporate both S and Si as the light elements into the Earth’s core during a moderately high-pressure differentiation, consistent with geochemical models predicting up to 15 wt.% of light elements in the Earth’s core with 2-5 wt.% S and 7-10 wt.% Si. In contrast, for small planets such as Mars and Ganymede, differentiation took place within the pressure range of the miscibility gap. The composition of these cores is likely to be S-rich but Si-poor.     

Experimental reproduction of textures of chondrules

The textures of chondrules have been reproduced by crystallizing melts of three different compositions at 1 atm with cooling rates ranging from 400 to 20°C/min under 10^?9 to 10^?12 atmP_O2. A porphyritic olivine texture has been formed from a melt of olivine-rich composition (SiO₂ = 45 wt.%), a barred-olivine texture from melt of intermediate composition (SiO₂ = 47 wt.%), and radial-olivine texture from melt of pyroxene-rich composition (SiO₂ = 57 wt.%). The cooling rate for producing barred olivine is most restricted; the rate ranges from 120 to 50°C/min. Other textures can be formed with wider ranges of cooling rate. The results of the experiments indicate that some of the major types of textures of chondrules can be formed with cooling rate of about 100°C/min. With this cooling rate, the texture varies depending on the composition of melt.     

Study on the rheology of subducting slabs

We calculate thermal and phase structures of subducting slabs for different subducting velocities by a modified coupling code of the kinetic phase-transformation equations and the heat-diffusion equation with latent-heat release. Whereafter, we estimate their rheology structures based on the thermal and phase structures from the mineral physical point of view. At shallow depth, the upper layer has a high effective viscosity greater than 10³⁴Pa · s; while the lower layer has a relatively low effective viscosity, which is greater than 10²⁶Pa · s nevertheless. The effective viscosities below the kinetic phase boundary of olivine to wadsleyite decrease obviously, and reach a minimum of 10²²Pa · s. Small areas with higher effective viscosities exist above the depth of about 700 km in subducting slabs, which are produced by lower temperatures that are related with endothermic phase transformation of spinel to perovskite and magnesiowustite. The 1% and 99% isograds of spinel proportion delineate tortuous belts with low effective viscosities, which would affect the geodynamic behavior of subducting slabs.     

Viscosity measurements of subliquidus magmas: Alkali olivine basalt from the Higashi-Matsuura district, Southwest Japan

We carried out viscosity measurements and sampling of a crystal suspension derived from alkali olivine basalt from the Matsuura district, SW Japan, at subliquidus temperatures from 1230 °C to 1140 °C under 1 atm with NNO oxygen buffered conditions. Viscosity increased from 31 to 1235 Pa s with a decrease in temperature from 1230 to 1140 °C. On cooling, olivine first appeared at 1210 °C, followed by plagioclase at 1170 °C. The crystal content of the sample attained 31 vol.% at 1140 °C (plagioclase 22%, olivine 9%). Non-Newtonian behaviors, including thixotropy and shear thinning, were pronounced in the presence of tabular plagioclase crystals. The cause of such behavior is discussed in relation to shear-induced changes in melt–crystal textures. Relative viscosities, η_r (= η_s / η_m, where η_s and η_m are the viscosities of the suspension and the melt, respectively), were obtained by calculating melt viscosities from the melt composition and temperature at 1 atm using the equation proposed by Giordano and Dingwell [Giordano, D., Dingwell, D.B., 2003. Non-Arrhenian multicomponent melt viscosity: a model. Earth and Planetary Science Letters, 208, 337–349.]. The obtained relative viscosities are generally consistent with the Einstein–Roscoe relation, which represents η_r for suspensions that contain equant and equigranular crystals, even though the crystal suspension analyzed in the present experiments contained tabular plagioclase and granular olivine of various grain sizes. This consistency is attributed to the fact that the effect of crystal shape was counterbalanced by the effect of the dispersion of crystal size. The applicability of the Einstein–Roscoe equation with respect to crystal shape is discussed on the basis of the present experimental results. Our experiments and those of Sato [Sato, H., 2005. Viscosity measurement of subliquidus magmas: 1707 basalt of Fuji volcano. Journal of Mineralogical and Petrological Sciences, 100, 133–142.] show that the relationship between relative viscosity and crystal fraction is consistent with the Einstein–Roscoe relationship for axial ratios that are smaller than the critical value of 4–6.5, but discrepancies occur for higher ratios.     

Hugoniot equation of state of olivine and its geodynamic implications

Large olivine samples were hot-pressed synthesized for shock wave experiments. The shock wave experiments were carried out at pressure range between 11 and 42 GPa. Shock data on olivine sample yielded a linear relationship between shock wave velocity D and particle velocity u described by D=3.56(?0.13)+2.57(?0.12)u. The shock temperature is determined by an energy relationship which is approximately 790°C at pressure 28 GPa. Due to low temperature and short experimental duration, we suggest that no phase change occurred in our sample below 30 GPa and olivine persisted well beyond its equilibrium boundary in metastable phase. The densities of metastable olivine are in agreement with the results of static compression. At the depth shallower than 410 km, the densities of metastable olivine are higher than those of the PREM model, facilitating cold slab to sink into the mantle transition zone. However, in entire mantle transition zone, the shock densities are lower than those of the PREM model, hampering cold slab to flow across the "660 km" phase boundary.     

A numerical model of the fractionation of olivine and molten sulfide from komatiite magma

A numerical model has been formulated that simulates the differentiation of mafic and ultramafic magmas by the fractionation of olivine and molten sulfide. The model is used to simulate the low-pressure differentiation of a komatiite magma series under both sulfide-undersaturated and sulfide-saturated conditions. Under sulfide-saturated conditions, the molecular ratio of olivine to sulfide removed from the silicate liquid is39 ± 2. Separation of this relatively small proportion of sulfide melt results in significantly different chemical trends in derivative liquids and fractionated material than are produced in the sulfide-undersaturated system, and this observation may be useful in mineral exploration. Comparison of the model results with published analyses of natural rocks indicate that the liquid equivalent members of the komatiite suite at Yakabindie, Western Australia, could be derivative liquids produced by fractional crystallization of olivine from a sulfide-undersaturated parental magma containing about 32 wt.% MgO. Derivation of a komatiitic pyroxenite with 20 wt.% MgO would require fractionation of 43.4 mol.% olivine whereas production of a komatiitic basalt with 12 wt.% MgO would involve removal of 58.5 mol.% olivine. Synvolcanic intrusive dunitic lenses at Yakabindie could have been produced by accumulation of material separated during about 3.8 mol.% fractionation of a similar parental magma, but the concentration of chalcophile elements in these bodies requires that the magma was sulfide-saturated.     

Role of water in the origin of podiform chromitite deposits

We report experiments in basalt oversaturated with water to duplicate the nodular ore textures of podiform chromitite ores. In immiscible basalt-water systems saturated with olivine and chromite, olivine will reside in the melt while chromite will collect in the fluid phase. Fractionation is physical and is driven by differential wetting properties of melt and fluid against silicate and oxide surfaces. There is no need to suppress olivine from the liquidus of a primitive basaltic melt as suggested by Irvine [Irvine, T.N., Geology 5 (1977) 273-277], to achieve chromite accumulations as observed in natural podiform ore deposits. The results imply that podiform chromitite ores will form where a primitive olivine-chromite-saturated mantle melt is sufficiently water-rich to exsolve a fluid phase during passage through the uppermost mantle. The most likely geodynamic environment for podiform chromite mineralization to take place is a supra-subduction zone setting.     

Dehydration melting of solid amphibolite at 2.0 GPa: Effects of time and temperature

The dehydration melting of the natural rock at high pressure is important to investigating the magma formation in the earth’s interior. Since the 1970s, a lot of geological scientists have paid more atten- tion to the dehydration melting of the natural rock[1―5]. Previous experiments of dehydration melting and observations of fieldwork argued that the dehy- dration melting of the rock was probably the most important fashion for the melting of the lower crust rock[6―12]. The genesis of most …     

Eruption of kimberlite magmas: physical volcanology, geomorphology and age of the youngest kimberlitic volcanoes known on earth (the Upper Pleistocene/Holocene Igwisi Hills volcanoes, Tanzania)

The Igwisi Hills volcanoes (IHV), Tanzania, are unique and important in preserving extra-crater lavas and pyroclastic edifices. They provide critical insights into the eruptive behaviour of kimberlite magmas that are not available at other known kimberlite volcanoes. Cosmogenic ³He dating of olivine crystals from IHV lavas and palaeomagnetic analyses indicates that they are Upper Pleistocene to Holocene in age. This makes them the youngest known kimberlite bodies on Earth by >30?Ma and may indicate a new phase of kimberlite volcanism on the Tanzania craton. Geological mapping, Global Positioning System surveying and field investigations reveal that each volcano comprises partially eroded pyroclastic edifices, craters and lavas. The volcanoes stand <40?m above the surrounding ground and are comparable in size to small monogenetic basaltic volcanoes. Pyroclastic cones consist of diffusely layered pyroclastic fall deposits comprising scoriaceous, pelletal and dense juvenile pyroclasts. Pyroclasts are similar to those documented in many ancient kimberlite pipes, indicating overlap in magma fragmentation dynamics between the Igwisi eruptions and other kimberlite eruptions. Characteristics of the pyroclastic cone deposits, including an absence of ballistic clasts and dominantly poorly vesicular scoria lapillistones and lapilli tuffs, indicate relatively weak explosive activity. Lava flow features indicate unexpectedly high viscosities (estimated at >10² to 10⁶?Pa?s) for kimberlite, attributed to degassing and in-vent cooling. Each volcano is inferred to be the result of a small-volume, short-lived (days to weeks) monogenetic eruption. The eruptive processes of each Igwisi volcano were broadly similar and developed through three phases: (1) fallout of lithic-bearing pyroclastic rocks during explosive excavation of craters and conduits; (2) fallout of juvenile lapilli from unsteady eruption columns and the construction of pyroclastic edifices around the vent; and (3) effusion of degassed viscous magma as lava flows. These processes are similar to those observed for other small-volume monogenetic eruptions (e.g. of basaltic magma).     

Shear viscosity of rhyolite-vapor emulsions at magmatic temperatures by concentric cylinder rheometry

The viscosity of natural rhyolitic melt from Lipari, Aeolian Islands and melt-bubble emulsions (30–50 vol% porosity) generated from Lipari rhyolite have been measured in a concentric cylinder rheometer at temperatures and shear rates in the range 925–1150°C and 10⁻³–10^−1.2 s⁻¹, respectively, in order to better understand the dependence of emulsion shear viscosity on temperature and shear rate in natural systems. Bubble-free melt exhibits Newtonian–Arrhenian behavior in the temperature range 950–1150°C with an activation energy of 395±30 kJ/mol; the shear viscosity is given by log η_m=−8.320+20624/T. Suspensions were prepared from natural rhyolite glass to which small amounts of Na₂SO₄ were added as a ‘foaming agent’. Reasonably homogeneous magmatic mixtures with an approximate log-normal distribution of bubbles were generated by this technique. Suspension viscosity varied from 10^6.1 to 10^8.37 Pa s and systematically correlates with temperature and porosity in the shear stress range (10^4.26–10^5.46 Pa) of the experiments. The viscosity of melt-bubble emulsions is described in terms of the relative viscosity, η_r=η_e/η_m where η_e is the emulsion viscosity and η_m is the viscosity of melt of the same composition and temperature. The dependence of relative viscosity on porosity for magmatic emulsions depends on the magnitude of the capillary number Ca≡G/(σr_b⁻¹η_m⁻¹), the ratio of viscous forces acting to deform bubbles to interfacial forces resisting bubble deformation. For inviscid bubbles in magmatic flows three regimes may be identified. For Ca<0.1, bubbles are nearly spherical and relative viscosity is an increasing function of porosity. For dilute systems, η_r=1+φ given by the classical result of Taylor [Proc. R. Soc. London A 138 (1932) 41–48]. For Ca in the range 0.1<Ca<10, emulsions behave as power law fluids and the relative viscosity depends on shear rate (or Ca) as well as porosity. At high Ca (Ca>10) an asymptotic regime is reached in which relative viscosity decreases with increasing porosity and is independent of Ca. Our experiments were carried out for 30<Ca<925 in order to quantify the maximal effect of bubbles in reducing the viscosity of magmatic emulsions relative to single-phase melt at identical conditions of shear rate and temperature. The viscosity of a 50 vol% emulsion is a factor of five smaller than that of melt alone. Rheometric measurements obtained in this study are useful in constraining models of magma transport and volcanic eruption mechanics relevant to transport of volatile-saturated magma in the crust and upper mantle.     

Metal-olivine associations and NiCo contents in two Apollo 12 mare basalts

Olivine crystals in mare basalts 12004,8 and 12022,12 are normally zoned with Cr-poor rims. The Ni content of rare 2–10-μm metal inclusions in olivine decreases markedly as Fe/Mg in their immediate olivine hosts increases. Each metal grain appears to have been enclosed by late olivine almost immediately after it crystallized. The fractionation trend for the olivine and metal contrasts with the subsolidus equilibration trend for pallasites. For the basalts, not even local equilibration of Fe, Ni and Co at metal/olivine interfaces can be detected by microprobe. Ni and Co concentrations range from about 300 ppm in olivine cores to about 70 ppm in rims. The limits of detection, at 95% confidence, are 36 ppm (Ni) and 25 ppm (Co). The distribution of Ni and Co in olivine, like that of Mg and Cr, records the depletion of these elements in the melt.Fractional solidification models, using the Ni and Co concentrations of the whole rock, and Ni and Co concentrations of the earliest formed olivine, metal and “opaques” as initial compositions, allow metal and olivine compositions to be predicted if the order of crystallization is known. Conversely the order of crystallization can be established if known olivine and metal compositions are reproduced. Calculated Ni and Co contents for metal and olivine in these basalts correspond to observed concentrations only where metal precipitation is delayed until the liquid has crystallized 4–5 wt.% olivine.     

The peculiarities of magma rise in presence of water

The viscosity of basalts (quartz and olivine tholeiite) was studied under pressure in dry conditions and in the presence of water. In dry conditions at 1400°C when pressure increases to 20 kbars the viscosity reduces by a factor of 2. In conditions of water saturation of basalt melts at 5 kbar the viscosity is smaller by a factor of ～ 50 than that in dry conditions. In the water undersaturated conditions when water content is fixed (3.3% H₂O) in melt the viscosity considerably decreases with pressure and takes intermediate value between those in dry and water saturated conditions. Experimental data recently obtained permit us to consider the peculiarities of physical properties of magma in the presence of water on a new base. Ascending magma can reach critical velocities of transition to the turbulent regime under negligible pressure drop, as a result of low viscosity. It is known at present that water influences on the viscosity of acidic melt under pressure of 1–8 kbars and at temperatures between 800–1200°C. Various authors gave physico-chemical evaluation of the dynamics of granite melts on the basis of these data. The viscosity of basalt melts and their dynamics under normal pressure is also well-known. The known new experimental data of basaltic melt viscosity under pressure in dry conditions (Kushiro et al., 1976;Khitarov et al., 1978) and in the presence of water (Khitarov et al., 1976) embrace broader intervals of physico-chemical conditions as on the pressure (up to 20–30 kbar) as well on the content of water (from 3% up to 12 %). These data permitted to evaluate on a new base the dynamics of magmatic melts under pressure.     

Solidus and liquidus temperatures and mineralogies for anhydrous garnet-lherzolite to 15 GPa

A review of experimental data for systems, pertaining to anhydrous fertile garnet-lherzolite shows strong convergence in the liquidus and solidus temperatures for the range 6.5–15 GPa. These can converge either to a common temperature or to temperatures which differ by only ～ 100°C. The major-element composition of magmas generated by even minor degrees of partial melting may be similar to the primordial bulk silicate Earth composition in an upper-mantle stratigraphic column extending over 160 km in depth.The convergence of the solidus and liquidus temperatures is a consequence of the highly variable $\text{d}\text{T}\text{d}\text{P}$ of the fusion curves for minerals which crystallize in peridotite systems. In particular, $\text{d}\text{T}\text{d}\text{P}$ for the forsterite fusion curve is much less than that for diopside and garnet. Whether or not the solidus and liquidus intersect, the liquidus mineralogy for undepleted garnet-lherzolite compositions changes from olivine at low pressures to pyroxene, garnet, or a complex pyroxene-garnet solid solution at pressures in excess of 10–15 GPa. Geochemical data for the earliest Archean komatiites are consistent with an upper-mantle phase diagram having garnet as a liquidus phase for garnet-lherzolite compositions at high pressures. All estimates of the anhydrous solidus and liquidus for the range 10–15 GPa are consistent with silicate liquid compressibility data, which indicate that olivine may be neutrally buoyant in ultramafic magmas at these pressures.     

Melting relations in the chloride–carbonate–silicate systems at high-pressure and the model for formation of alkalic diamond–forming liquids in the upper mantle

The experiments in the model system CaMgSi₂O₆–(Na₂CO₃, CaCO₃)–KCl are performed at 5 GPa and 1400–1600 °C in order to study the phase relations, including liquid immiscibility, in the chloride–carbonate–silicate systems with application to alkali and chlorine-rich liquids preserved in kimberlitic diamonds. Experiments in the boundary joins of the system demonstrated that both the carbonate–silicate and chloride–carbonate melts are homogeneous; while high-temperature (above 1800 °C) liquid immiscibility is assumed for the chloride–silicate join of the above system. Addition of silicate component into the chloride–carbonate melts and chloride component into the carbonate–silicate melts results in splitting of the homogeneous liquids into the immiscible chloride–carbonate brine and carbonate–silicate melt. Carbonate–silicate and chloride–carbonate branches of the miscibility gap converge within the carbonate-rich region of the system. Regular temperature evolution of the shape and size of the miscibility gap is deduced. With decreasing temperature, the convergence point moves toward more Si-rich compositions, expanding fields of homogeneous chloride–carbonate silica-saturated melts. This effect is governed by the precipitation of the silicate phases even from silica-bearing chloride–carbonate melts. In addition, experiments revealed regular evolution of both Cl-bearing carbonate–silicate melt and Si-bearing chloride–carbonate brine toward the low-temperature chlorine–bearing carbonatitic liquid with decreasing temperature. These trends are similar to the evolution of the melt and brine inclusions in some diamonds from Botswana, Brazil, Canada, and Yakutia, indicating their growth during cooling. The model for interaction of the chloride–carbonate brine with the mantle rocks is developed on the basis of the present experimental data. This model is applied to the chlorine-enriched kimberlites of the Udachnaya–East pipe.