Crystal chemistry of sodium in the Earth's interior: The structure of Na2MgSi5O12 synthesized at 17.5 GPa and 1700  C

Bindi, Luca; Dymshits, A. M.; Бобров, А. В.; Litasov, Konstantin D.; Shatskiy, Anton; Ohtani, Eiji; Litvin, Yu. A.

doi:10.2138/am.2011.3716

Cited by 34 publications

(18 citation statements)

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“…As D 0 , r 0 and E are highly correlated with one another, instead of fitting each literature dataset for all three variables simultaneously a predictive model was employed to estimate E (van Westrenen and , adding a term for the Na content of garnet (X Na = 0.5*[Na+K], where Na and K are calculated per formula unit with 12 oxygens) to equation 3 Thomson et al revision 1 submitted 19/08/2015 8 (equations 2 and 3). The coefficient of X Na was estimated based on the size of the Na 2 MgSi 5 O 12 garnet X-site (Bindi et al, 2011). This predicted value of E is used to fit the experimental data for D 0 and r 0 using equation 1 …”

Section: Mineral/melt Partition Coefficientsmentioning

confidence: 99%

Trace element composition of silicate inclusions in sub-lithospheric diamonds from the Juina-5 kimberlite: Evidence for diamond growth from slab melts

Thomson

Kohn

Bulanova

et al. 2016

Lithos

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Trace element composition of silicate inclusions in sublithospheric diamonds from the juina-5 kimberlite: Evidence for diamond growth from slab melts, LITHOS (2016), doi: 10.1016/j.lithos.2016.08.035 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A C C E P T E DM A N U S C R I P T ACCEPTED MANUSCRIPT ABSTRACTThe trace element compositions of inclusions in sub-lithospheric diamonds from the Juina-5 kimberlite, Brazil, are presented. Literature data for mineral/melt partition coefficients were collated, refitted and employed to interpret inclusion compositions. As part of this process an updated empirical model for predicting the partitioning behaviour of trivalent cations for garnet-melt equilibrium calibrated using data from 73 garnet-melt pairs is presented. High levels of trace element enrichment in inclusions interpreted as former calcium silicate perovskite and majoritic garnet preclude their origin as fragments of an ambient deep mantle assemblage. Inclusions believed to represent former bridgmanite minerals also display a modest degree of enrichment relative to mantle phases. The trace element composition of 'NAL' and 'CF phase' minerals are also reported. Negative Eu, Ce, and Y/Ho anomalies alongside depletions of Sr, Hf and Zr in many inclusions are suggestive of formation from a low-degree carbonatitic melt of subducted oceanic crust. Observed enrichments in garnet and 'calcium perovskite' inclusions limit depths of melting to less than ~ 600 km, prior to calcium perovskite saturation in subducting assemblages. Less enriched inclusions in sub-lithospheric diamonds from other global localities may represent deeper diamond formation. Modelled source rock compositions that are capable of producing melts in equilibrium with Juina-5 'calcium perovskite' and majorite inclusions are consistent with subducted MORB. Global majorite inclusion compositions suggest a common process is responsible for the formation of many superdeep diamonds, irrespective of geographic locality. Global transition zone inclusion compositions are reproduced by fractional crystallisation from a single parent melt, suggesting that they record the crystallisation sequence and melt evolution during this interaction of slab melts with ambient mantle. All observations are consistent with the previous hypothesis that many superdeep diamonds are created as slab-derived carbonatites interact with peridotitic mantle in the transition zone.

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Section: Mineral/melt Partition Coefficientsmentioning

confidence: 99%

Trace element composition of silicate inclusions in sub-lithospheric diamonds from the Juina-5 kimberlite: Evidence for diamond growth from slab melts

Thomson

Kohn

Bulanova

et al. 2016

Lithos

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“…It expands a set of petrologically significant phases, such as Na-bearing majoritic garnet (e.g., Bindi et al 2011) and Na(Mg x Si x Al 1−2x ) Si 2 O 6 pyroxene (e.g., Yang et al 2009), which are able to contain notable VI Si at pressures corresponding to the sublithospheric mantle depths.…”

Section: Resultsmentioning

confidence: 99%

“…Therefore, synthesis and structural characterization of dense phases, which are able to accommodate Na and K, are one of the priorities for highpressure experimental petrological studies. A great deal of various Na-bearing (see short reviews in Yang et al 2009 andBindi et al 2011) and K-bearing (see review in Harlow and Davies 2004) phases have been reported from experiments since 1990s. Most of these phases are just synthetic curiosities, whose presence in the real mantle assemblages has never been established.…”

Section: Introductionmentioning

confidence: 99%

“…Most of these phases are just synthetic curiosities, whose presence in the real mantle assemblages has never been established. Synthesis of other phases such as Na-bearing majoritic garnet (e.g., Bindi et al 2011), Na(Mg x Si x Al 1−2x )Si 2 O 6 pyroxene (e.g., Yang et al 2009), Na-bearing ferropericlase (e.g., Brey et al 2004), K-bearing pyroxene (e.g., Safonov et al 2011) bears a direct impact on understanding of the K and Na behavior in the deep mantle.…”

Section: Introductionmentioning

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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“…Basically, Li-maj and Na-maj have similar Raman patterns (Fig. 6), and thus they may be considered as analogs, even though Li-maj is cubic with space group Ia3d (Yang et al 2009a) while Na-maj is tetragonal with space group I4 1 /acd (Bindi et al 2011). Additionally Na-maj spectrum has well attended O-Si-O asymmetric bending (T 2g -n 4 ) mode (827 cm -1 ) typical for tetragonal majoritic garnets (Hofmeister et al 2004).…”

Section: Resultsmentioning

confidence: 99%

In situ observation of the pyroxene-majorite transition in Na2MgSi5O12 using synchrotron radiation and Raman spectroscopy of Na-majorite

Dymshits

Sharygin

Litasov

et al. 2015

American Mineralogist

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In situ X-ray diffraction study of the pyroxene to majorite transition in Na 2 MgSi 5 O 12 was carried out in Kawai-type high-pressure apparatus coupled with synchrotron radiation. The phase boundary between Na-pyroxene and Na-majorite was determined over the temperature interval of 1073-1973 K and was described by a linear equation P (GPa) = 12.39 + 0.0018×T (K). The Clapeyron slope (dP/ dT) determined in this study is similar to the one predicted by computer simulations (Vinograd et al. 2011) but smoother than the one obtained by quenched experiments (Dymshits et al. 2010). The presence of sodium in the system lowers the pressure of pyroxene-to-majorite transformation. For the first time Na-majorite was characterized using Raman spectroscopy. Raman peaks of Na-majorite are broader than pyrope due to the substitution of Mg 2+ for Na + at the X site. Both Si-O symmetric stretching (A 1g -n 1 ) and O-Si-O symmetric bending (A 1g -n 2 ) modes of Na-majorite are significantly shifted to higher frequencies relative to corresponding bands of pyrope. In contrast the A 1g -R (SiO 4 ) mode of Na-majorite (342 cm -1 ) displays a lower frequency than that of pyrope (365 cm -1 ). Our results enable further understanding of the mechanisms responsible for phase transformations in the Earth's transition zone and lower mantle.

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Crystal chemistry of sodium in the Earth's interior: The structure of Na2MgSi5O12 synthesized at 17.5 GPa and 1700 C

Cited by 34 publications

References 24 publications

Trace element composition of silicate inclusions in sub-lithospheric diamonds from the Juina-5 kimberlite: Evidence for diamond growth from slab melts

Trace element composition of silicate inclusions in sub-lithospheric diamonds from the Juina-5 kimberlite: Evidence for diamond growth from slab melts

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

In situ observation of the pyroxene-majorite transition in Na2MgSi5O12 using synchrotron radiation and Raman spectroscopy of Na-majorite

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