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

Сафонов, О. Г.; Perchuk, L. L.; Litvin, Yu. A.

doi:10.1016/j.epsl.2006.10.020

Cited by 94 publications

(51 citation statements)

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“…Zedgenizov et al (2014) proposed that the Ca-rich assemblages including merwinite represented products of the interaction of mantle peridotites with Ca-rich carbonatite melt derived from subducted slabs. This conclusion is consistent with the results of experimental studies in a number of carbonate-silicate and carbonate-silicate-chloride systems at 2-7 GPa where merwinite appears as a product of interaction of various silicates (forsterite, enstatite, diopside, diopside-jadeite pyroxene) with CaCO 3 -rich carbonate-silicate and carbonate-chloride melts (Safonov et al 2007(Safonov et al , 2009Safonov 2011;Sharygin et al 2012). Compositions of these melts are close analogs of the melts found as microinclusions in kimberlitic fibrous diamonds worldwide (see review, comparison and references in Safonov et al 2007Safonov et al , 2009.…”

Section: Petrological Applicationssupporting

confidence: 88%

“…The unit cell is outlined. The vertical axis is the c axis However, the most extensive solid solution forms at 7 GPa, and miscibility between end-members seems to drastically decrease with the decreasing pressure, since no alkalirich merwinite has been found at 5.5 and 5 GPa (Safonov et al 2007(Safonov et al , 2009. No coexisting alkali-rich and alkalipoor merwinites were detected in the run products.…”

Section: Discussion and Applicationsmentioning

confidence: 99%

“…Open circles-compositions of phases produced at 7 GPa and 1370 °C (large open circle shows composition of the alkali-rich merwinite); gray circles-compositions of phases produced at 7 GPa and 1460 °C; gray squarescompositions of phases produced at 5.5 GPa. Black squares-merwinites produced in the experiments on interaction of various silicate with the melts CaCO 3 + Na 2 CO 3 + KCl at 5 GPa (Safonov et al 2007(Safonov et al , 2009). Cross-merwinite reported by Moriyama et al (1992), white rhomb-composition of merwinite inclusion in diamond from the São Luiz alluvial deposit, Juina Province, Brazil (Zedgenizov et al 2014) Si 2.00 O 8 (Table 1), which can be represented as a solid solution of Ca 3 MgSi 2 O 8 (Mrw) and a hypothetical "alkali merwinite" (Na,K) 2 CaSiSi 2 O 8 (AMrw).…”

Section: Number Of Least-squares Parameters 131mentioning

confidence: 99%

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Merwinite-structured phases as a potential host of alkalis in the upper mantle

Bindi

Сафонов

Zedgenizov

2015

Contrib Mineral Petrol

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c = 9.130(2) Å, β = 92.36(1)°, V = 604.3(2) Å 3 , and Z = 4. The structure was refined to R 1 = 0.031 using 2619 independent reflections. In the structure, Na is hosted at the large Ca sites, whereas Si replaces Mg at the octahedral site and occurs in the usual tetrahedral coordination. Ordering-induced distortion provokes a change in coordination of the (Ca, Na) atoms with respect to pure merwinite. Merwinite phases with lower K + Na contents (0.08-0.18 a.p.f.u.) coexist with forsterite, clinopyroxene and immiscible carbonate-chloride and silicate melts at higher temperatures (up to 1510 °C) at 7 and 5.5 GPa. These phases (including alkali-rich ones at solidus) show a general formula [Ca 3−2x (Na,K) 2x ][Mg 1−x Si x ]Si 2 O 8 (with x up to 0.45), where the Na + K content negatively correlates with Ca and positively correlates with Si. The present experimental and crystal-chemical data prove that merwinite-structured phases may be efficient hosts for alkalis in the upper mantle. They are mineralogical indicators of either the interaction of mantle peridotites with alkaline carbonatitic liquids or highpressure crystallization of silica-undersaturated CaO and alkali-rich melts.Keywords Merwinite structure · Alkalis · Upper mantle · High-pressure · Crystal structure · Microprobe analysis · Synthesis AbbreviationsAk Åkermanite Cal Calcite Di Diopside En Enstatite Fo Forsterite Mrw Merwinite Per Periclase Prv Perovskite Abstract Two previously unknown Na-and K-rich phases were synthesized near the solidus of the model CMAS lherzolite interacted with the CaCO 3 + Na 2 CO 3 + KCl melt at 7 GPa. They coexist with forsterite, garnet and chloride-carbonate melt. Stoichiometry and unit-cell parameters measured by means of powder diffraction indicate that one of the phases corresponds to (K,Na) 2 Ca 4 Mg 2 Si 4 O 15 (with about 0.1 a.p.f.u. Al). Although single-crystal X-ray measurements of this phase did not allow the solution of the crystal structure, we suggest that the structure of this phase includes mixed SiO 4 and Si 2 O 7 units. Single-crystal diffraction experiments of the other alkali-rich phase with composition (Ca 2.06 Na 0.86 K 0.08 ) Σ=3.00 (Mg 0.53 Si 0.45 Al 0.03 ) Σ=1.01 Si 2.00 O 8 showed that it exhibits the merwinite structure, space group P2 1 /a, with lattice parameters a = 12.987(2), b = 5.101(1),

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Section: Petrological Applicationssupporting

confidence: 88%

Section: Discussion and Applicationsmentioning

confidence: 99%

Section: Number Of Least-squares Parameters 131mentioning

confidence: 99%

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Merwinite-structured phases as a potential host of alkalis in the upper mantle

Bindi

Сафонов

Zedgenizov

2015

Contrib Mineral Petrol

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“…K-rich pyroxenes might form on the liquidus of a silicate magma mixed or coexisting with K-rich brine (42). Recent attention to chlorides is also due to new evidence of their participation in metasomatic processes in the mantle (43)(44)(45)(46) and deep zones of the crust (47). Speculation of the possible nature of Cl in the mantle has also been recently reviewed (48).…”

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confidence: 99%

The role of mantle ultrapotassic fluids in diamond formation

Palyanov

Shatsky

Sobolev

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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Analysis of data on micro-and nano-inclusions in mantle-derived and metamorphic diamonds shows that, to a first approximation, diamond-forming medium can be considered as a specific ultrapotassic, carbonate/chloride/silicate/water fluid. In the present work, the processes and mechanisms of diamond crystallization were experimentally studied at 7.5 GPa, within the temperature range of 1,400 -1,800°C, with different compositions of melts and fluids in the KCl/K 2CO3/H2O/C system. It has been established that, at constant pressure, temperature, and run duration, the mechanisms of diamond nucleation, degree of graphite-to-diamond transformation, and formation of metastable graphite are governed chiefly by the composition of the fluids and melts. The experimental data suggest that the evolution of the composition of deep-seated ultrapotassic fluids/melts is a crucial factor of diamond formation in mantle and ultrahigh-pressure metamorphic processes. high-pressure experimentA n important stage in solving problems of diamond genesis is constructing a clear physical model of diamond formation (1). One of the key parameters to be modeled is the composition of the diamond crystallization medium, with a fluid being largely considered as a crucial agent in diamond formation. It is generally agreed that the mantle media of diamond crystallization were volatile-saturated melts or fluids (1-7). Carbonbearing fluids and carbonates could be sources of carbon, and the medium could have been saturated with it by redox reactions. Recent studies have been aimed at searching and examining fluid and fluid-containing inclusions in genetically different diamonds. Also, experiments have been performed to model the processes of diamond crystallization in the media compositionally corresponding to the inclusions. It is the combination of these two approaches that permits us to gain deeper insight into diamond genesis and to better understand the specific character of processes of deep-seated mineral formation.Studies of mineral inclusions in diamonds have determined the main types of diamondiferous parageneses: ultramaffic, eclogitic (4,8,9), and intermediate websterite (10) and calc-silicate types (11). Some mineral inclusions, e.g., intergrowths of phlogopite with pyroxene (8, 12, 13) and phlogopite with calcite (14), are unambiguously evidence that K and H 2 O were present in the diamond-forming medium. It is pertinent to note that, as early as 30 years ago, neutron activation analysis of diamonds without visible inclusions, taken from three South African deposits, revealed a mixture of mostly K and of other components, which was interpreted as evidence of the presence of entrapped melt (15). Principally, more recent information has accrued from micro-and nano-inclusions in mantle-derived and metamorphic diamonds. Analysis of the composition of the inclusions in fibrous or cloudy mantle diamonds shows that, at the time of entrapment, the inclusion matter was a specific fluid whose composition belongs to one of the three main types: (i) ...

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“…Potassium is also an incompatible element in silicate melts and may have a strong influence on melting behaviour (and melt density) at deep mantle conditions (Karato et al 2006). Potassium is considered as a leading alkalic component in metasomatic fluids (Frost 2006) and in diamond-forming Cl-rich brine, silicate and carbonate-silicate liquids, as recorded by inclusions in kimberlitic diamonds worldwide (Navon et al 2003;Safonov et al 2007 and references therein). The high efficiency of K-rich silicate-carbonate melts for diamond formation was established in experimental runs at 7.0 and 8.5 GPa and 1,500-1,800°C (Bobrov and Litvin 2009) where diamond coexisted with orthopyroxene, phase-X and carbonate-silicate melt.…”

Section: Introductionmentioning

confidence: 99%

Equation of state of Fe3+-bearing phase-X

et al. 2012

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We investigated the high-pressure behaviour of Fe 3? -bearing hydrous phase-X, (K 1.307 Na 0.015 )(Mg 1.504-Fe 0.373 3? Al 0.053 Ti 0.004 4? )Si 2 O 7 H 0.36 , up to 34 GPa at room temperature by synchrotron X-ray powder diffraction. The lattice parameters behave anisotropically, with the [001] direction stiffer than [100]. In the 10 -4 to 22 GPa pressure range, the axial bulk moduli are K 0a = 112(3) GPa and K 0 = 4, and K 0c = 158(2) GPa and K 0 = 4, and the anisotropy of the lattice parameters is b 0c :b 0a = 0.71:1. The cell volumes are fitted by a second-order Birch-Murnaghan equation of state giving a bulk modulus of K 0 = 127(1) GPa and K 0 = 4 in the same pressure range. After 22 GPa, a discontinuity in volume and lattice parameters can be recognized. Sample did not become amorphous up to 34 GPa. The coupled substitution K ? Mg = [] ? Fe 3? has only a limited influence on the bulk modulus and structural stability of phase-X.

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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

Cited by 94 publications

References 43 publications

Merwinite-structured phases as a potential host of alkalis in the upper mantle

Merwinite-structured phases as a potential host of alkalis in the upper mantle

The role of mantle ultrapotassic fluids in diamond formation

Equation of state of Fe3+-bearing phase-X

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