Report for the Joint Use/Research of the Institute for Planetary Materials,
Okayama University
2019 fiscal yearfirst term
31/May/2020

Category: International Joint Research
Name of the research project: The interaction of magnesium carbonates with reduced peridotite
and eclogite containing metallic iron at P-T parameters of the Earth's upper mantle.
Principal applicant: Dr. Naira Martirosyan
Affiliated institution and department:
GFZ German Research Centre for Geosciences, Telegrafenberg, 14473, Potsdam, Germany
Collaborator
Name: Prof. Dr. Takashi Yoshino
Affiliated institution and department:
Institute for planetary materials

Research report:
1. Introduction
The findings of syngenetic inclusions of calcuim and magnesium carbonates in the
diamonds from kimberlites (Bulanova et al., 2010; Jablon and Navon, 2016; Stachel et al., 1998,
2000; Zedgenizov et al., 2014 a, b), and carbonate - bearing rocks from the ultrahigh-pressure
metamorphic terranes, such as The Kokchetav Massif (Korsakov et al., 2009, 2011; Sobolev andShatsky, 1990), confirm the existence of carbonates deep in the upper mantle, transition zone, oreven the lower mantle and their role in diamond formation.
Although MgCO3 and CaCO3 are stable in a wide range of P-T conditions (Boulard et al.,2015; Lobanov et al., 2017), the deeper part of the mantle can be too reduced to favor presence ofcarbonates. Studies of the ferric – ferrous equilibria reconstructed from the garnet peridotites
suggest that mantle rocks become progressively more reduced (Frost and McCammon, 2008).
Thermodynamic calculations and experiments suggest that mantle becomes metal saturated at 250
km depth and in all mantle regions below (Frost et al., 2004; Rohrbach et al., 2007). Findings ofmetallic iron and iron carbides as inclusions in diamonds (Kaminsky and Wirth, 2011; Smith et al.,2016; Stachel et al., 1998) are in good agreement with this concept.
Thus, it is evident that the significant chemical heterogeneity in the redox conditions exists
in the mantle, and the oxygen fugacity varies from the CCO buffer in the carbonate-bearing

subducted rocks to the Fe-FeO buffer in the Fe0-saturated surrounding mantle. As consequence ofthe existing redox gradient redox reactions will occur, and diamonds or other reduced carbon
species can be formed directly by the reduction of carbonates or carbonatite melts. The mechanismand kinetics of these processes are extremely important for understanding the carbon behavior anddistribution in the deep Earth.
Current state of issue
Most of the previous experimental and theoretical studies on the reactions of carbonates withmetallic iron examine simplified carbonate-Fe0 systems: 1) MgCO3–Fe0 at 6 and 25 GPa (Gao et al.,2016; Martirosyan et al., 2015b); 2) CaCO3–Fe0 at 6 and 16 GPa (Martirosyan et al., 2015a, 2016);
3) (Ca,Mg)CO3–Fe0 at 6–7 GPa and 40–110 GPa (Dorfman et al., 2015; Palyanov et al., 2013). All
the works above revealed the occurrence of the redox reactions with the formation ofgraphite/diamond, Fe3C/Fe7C3 carbide and magnesiowistite or calcium wustite, depending on theinitial composition of the carbonate.
Despite the wide interest to the carbonates reduction in the presence of metallic iron, there
are only few works, which model the process in the presence of silicates. Among them areinvestigation of Bataleva et al. (2015) in the (Mg,Ca)CO3–SiO2–Al2O3–Fe0 system at 6.3 -7.5 GPa,and experiments with carbonated peridotite conducted by Rohrbach and Schmidt (2011) at
14–23 GPa.
It is evident that for the further understanding of this issue, experimental study in the model
systems, close to natural, are required.
Aims of the projectIn the present project we studied the interaction of Fe with magnesite in the complex natural
systems with peridotite and eclogite composition at 6-10 GPa and 900-1400°С. Based on the results
the model of the redox reaction of calcium and magnesium carbonates with metallic iron will bereconstrtucted.

2. Experimental results
Methods
High-pressure experiments were carried out using uniaxial presses equipped with the
split-sphere guide blocks, USSA-1000 installed at the Institute for Planetary Materials, Okayama
University, Misasa, Japan (IPM). Octahedra made of Cr-doped MgO semi-sintered ceramics were
employed as pressure-transmitting media. The cell assembly with a/b = 18/11, where a is anoctahedron edge length and b is a truncation edge length, were employed at 6 and 10 GPa. Graphite
tubular heaters were used to generate high temperatures. The temperature was controlled using a
W97Re3–W75Re25 thermocouple with a junction at the centre of the heater. The high-pressure cell
contained two graphite capsules, placed symmetrically to the thermocouple junction, and separated
from the heater by a MgO sleeve.
Natural magnesite, Fe powder or plates (99.9% Rare Metallic Co) were used as starting
reagents. Silicate part of the sample was presented by San Carlos olivine (Fo 90.1%), or natural
eclogite and dunite with known compositions (Ragozin et al., 2006). The starting reagents weredried before the experiments at 320 °C.
To see more clearly the reaction front we used layered loading of the experimental capsules.
Iron and carbonates were initially separated by the silicate layer. The following systems werestudied:•Magnesite – dunite/olivine – Fe;•

Magnesite – eclogite – Fe;

Overall 12 samples were obtained and analysed by EDS.

3. Results and discussion
System Magnesite – peridotite – Fe
The Magnesite – olivine – Fe andMagnesite – dunite – Fe systems were studied at
6 and 10 GPa in the temperature range
1100–1400 °С in experiments with various
durations from 3 to 26 hours (Fig. 1). The
formationofmagnesiowüstite

(Mws)

and

graphite (Gr) was observed. Gr crystallized up to

Fig. 1 BSE images of the samples from the 6GPa experiments: (a)MgCO3–dunite–Fe (1100ºС, 26 h) ; (b) MgCO3–olivine–Fea temperature of 1400 °C, at which the diamond (Dia) was detected. In the silicate part of thesample, modal composition of olivine changes toward more Fe rich variety.
Based on our observations the following reactions could be proposed:
MgCO3 + Fe0 →(Fe,Mg)O +С0(1)

FeO + Mg2SiO4 → Fe2SiO4 +MgO

(2)

The reaction rate in the Magnesite – peridotite – Fe system increases exponentially withtemperature. After 26 hours of heating at 1100°C, only a small amount of Mws and Gr was foundnear the carbonate / silicate interface (Fig. 1a). At the same time, a significant part of MgCO3 andFe remain unaltered. At 1200 °C, the reaction zone reaches 200 microns after 12 hours of heating(Fig. 1b), while in 20 hours MgCO3 and Fe completely react.

System Magnesite – eclogite – FeTheexperiments

Magnesite-eclogite-Fe

in

the

systemwerecarried out at 6 GPa and 1100 ° C with aheating duration of 3 to 26 hours. Same as
in Magnesite - peridotite – Fe system, theformation of Mws and Gr is observed.

Fig. 2 BSE images of the samples from the Dolomite – eclogite-Fe experiment at

Mws reacted with diopside (Cpx),

1100ºС, 6GPa: (a)after 3h of heating; (b) 26h.

resulting in the formation of Ol. In the 26h experiment, we detected only relicts of magnesite andiron. Cpx was completely replaced by Ol. It is clear that the reaction carbonate-iron reaction isfaster in the eclogite system, compared to that in peridotite system.
The redox reaction in the system could be described by the equation (1). Additionally, theformation of olivine and disappearance of Cpx allows to propose the following reaction:(Fe,Mg)O + CaMgSi2O6 + Mg3Al2(SiO4)3 → (Mg,Fe)2SiO4 + (Ca,Fe)3Al2(SiO4)3 (3)4. Conclusions
In this project, we conducted experiments in the MgCO3 - peridotite / eclogite - Fe systems
at 6-10 GPa using multi-punch presses. The layered loading of reagents in experiments withdifferent durations and temperatures made it possible to establish the sequence of reactions
occurring in the systems under study.
The redox reaction of carbonate with Fe in all experiments was accompanied by theformation of Gr or Dia and Mws. It was found that oxide is not stable in silicate systems under theparameters of the upper mantle and react with Ol, Cpx and to form Fe-Ol.
Based on the obtained data, it can be concluded that in natural systems where carbonates andiron are separated by silicate media, the reaction is limited by slow diffusion rates in silicates andwill not have a significant effect on the preservation of magnesite in the conditions of subduction
zones (hot geotherm - 6 GPa, 1100 °C). At the same time, under the parameters of the mantle
adiabat, the reaction rate is sufficient to lead to a complete or significant substitution of magnesite
by Dia and Mws / Ol.

References
Alt, J.C., Teagle, D.A., 1999. The uptake of carbon during alteration of ocean crust.
Geochimica Et Cosmochimica Acta 63, 1527-1535.
Bataleva, Y.V., Palyanov, Y.N., Sokol, A., Borzdov, Y.M., Bayukov, O., 2015. The role ofrocks saturated with metallic iron in the formation of ferric carbonate-silicate melts: experimental
modeling under PT-conditions of lithospheric mantle. Russian Geology and Geophysics 56,
143-154.
Boulard, E., Pan, D., Galli, G., Liu, Z., Mao, W.L., 2015. Tetrahedrally coordinatedcarbonates in Earth’s lower mantle. Nature communications 6.
Bulanova, G.P., Walter, M.J., Smith, C.B., Kohn, S.C., Armstrong, L.S., Blundy, J., Gobbo,
L., 2010. Mineral inclusions in sublithospheric diamonds from Collier 4 kimberlite pipe, Juina,
Brazil: subducted protoliths, carbonated melts and primary kimberlite magmatism. Contributions toMineralogy and Petrology 160, 489-510.
Dasgupta, R., Hirschmann, M.M., 2006. Melting in the Earth's deep upper mantle caused bycarbon dioxide. Nature 440, 659-662.
Dasgupta, R., Hirschmann, M.M., 2010. The deep carbon cycle and melting in Earth's
interior. Earth Planet Sc Lett 298, 1-13.
Dorfman, S.M., Badro, J., Nabiei, F., Prakapenka, V., Gillet, P., 2015. Iron-carbonate
interaction at Earth's core-mantle boundary. AGU Fall Meeting Abstracts, V21C-3041.
Frost, D.J., Liebske, C., Langenhorst, F., McCammon, C.A., Tronnes, R.G., Rubie, D.C.,
2004. Experimental evidence for the existence of iron-rich metal in the Earth's lower mantle. Nature
428, 409-412.
Frost, D.J., McCammon, C.A., 2008. The redox state of Earth's mantle. Annual Review ofEarth and Planetary Sciences 36, 389-420.
Gao, J., Niu, J.J., Qin, S., Wu, X., 2016. Ultradeep diamonds originate from deep subducted
sedimentary carbonates. Science China Earth Sciences, 1-11.
Hilton, D.R., Fischer, T.P., Marty, B., 2002. Noble gases and volatile recycling at
subduction zones. Reviews in Mineralogy and Geochemistry 47, 319-370.

Jablon, B.M., Navon, O., 2016. Most diamonds were created equal. Earth Planet Sc Lett
443, 41-47.
Johnston, F.K.B., Turchyn, A.V., Edmonds, M., 2011. Decarbonation efficiency insubduction zones: Implications for warm Cretaceous climates. Earth Planet Sc Lett 303, 143-152.
Kaminsky, F.V., Wirth, R., 2011. Iron carbide inclusions in lower-mantle diamond from
Juina, Brazil. The Canadian Mineralogist 49, 555-572.
Kelemen, P.B., Manning, C.E., 2015. Reevaluating carbon fluxes in subduction zones, whatgoes down, mostly comes up. Proceedings of the National Academy of Sciences 112,
E3997-E4006.
Kerrick, D.M., Connolly, J.A.D., 2001a. Metamorphic devolatilization of subducted marine
sediments and the transport of volatiles into the Earth's mantle. Nature 411, 293-296.
Kerrick, D.M., Connolly, J.A.D., 2001b. Metamorphic devolatilization of subducted oceanic
metabasalts: implications for seismicity, arc magmatism and volatile recycling. Earth Planet Sc Lett
189, 19-29.
Korsakov, A.V., De Gussem, K., Zhukov, V.P., Perraki, M., Vandenabeele, P., Golovin,
A.V., 2009. Aragonite-calcite-dolomite relationships in UHPM polycrystalline carbonate inclusions
from the Kokchetav Massif, northern Kazakhstan. European Journal of Mineralogy 21, 1301-1311.
Korsakov, A.V., Vandenabeele, P., Perraki, M., Moens, L., 2011. First findings ofmonocrystalline aragonite inclusions in garnet from diamond-grade UHPM rocks (Kokchetav
Massif, Northern Kazakhstan). Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy 80, 21-26.
Litasov, K.D., 2011. Physicochemical conditions for melting in the Earth’s mantle
containing a C–O–H fluid (from experimental data). Russian Geology and Geophysics 52, 475-492.
Lobanov, S.S., Dong, X., Martirosyan, N.S., Samtsevich, A.I., Stevanovic, V., Gavryushkin,
P.N., Litasov, K.D., Greenberg, E., Prakapenka, V.B., Oganov, A.R., 2017. Raman spectroscopy
and x-ray diffraction of sp 3 CaC O 3 at lower mantle pressures. Physical Review B 96, 104101.
Martirosyan, N., Litasov, K., Shatskiy, A., Ohtani, E., 2015a. Reactions of iron with calcium
carbonate at 6 GPa and 1273–1873 K: implications for carbonate reduction in the deep mantle.
Russian Geology and Geophysics 56, 1322-1331.
Martirosyan, N., Yoshino, T., Shatskiy, A., Chanyshev, A., Litasov, K., 2016. The CaCO
3–Fe interaction: Kinetic approach for carbonate subduction to the deep Earth’s mantle. Physics ofthe Earth and Planetary Interiors 259, 1-9.

Martirosyan, N.S., Litasov, K.D., Shatskiy, A., Ohtani, E., 2015b. The reactions between
iron and magnesite at 6 GPa and 1273–1873 K: Implication to reduction of subducted carbonate in
the deep mantle. Journal of Mineralogical and Petrological Sciences 110, 49-59.
Palyanov, Y.N., Bataleva, Y.V., Sokol, A.G., Borzdov, Y.M., Kupriyanov, I.N., Reutsky,
V.N., Sobolev, N.V., 2013. Mantle–slab interaction and redox mechanism of diamond formation.
Proceedings of the National Academy of Sciences 110, 20408-20413.
Palyanov, Y.N., Sokol, A., Borzdov, Y.M., Khokhryakov, A., Shatsky, A., Sobolev, N.,
1999a. The diamond growth from Li2CO3, Na2CO3, K2CO3 and Cs2CO3 solvent-catalysts at P= 7
GPa and T= 1700–1750oC. Diamond and Related Materials 8, 1118-1124.
Palyanov, Y.N., Sokol, A., Borzdov, Y.M., Khokhryakov, A., Sobolev, N., 1999b. Diamondformation from mantle carbonate fluids. Nature 400, 417-418.
Plank, T., Langmuir, C.H., 1998. The chemical composition of subducting sediment and its
consequences for the crust and mantle. Chemical Geology 145, 325-394.
Rohrbach, A., Ballhaus, C., Golla-Schindler, U., Ulmer, P., Kamenetsky, V.S., Kuzmin,
D.V., 2007. Metal saturation in the upper mantle. Nature 449, 456-458.
Rohrbach, A., Schmidt, M.W., 2011. Redox freezing and melting in the Earth's deep mantle
resulting from carbon-iron redox coupling. Nature 472, 209-212.
Smith, E.M., Shirey, S.B., Nestola, F., Bullock, E.S., Wang, J., Richardson, S.H., Wang, W.,
2016. Large gem diamonds from metallic liquid in Earth’s deep mantle. Science 354, 1403-1405.
Sobolev, N.V., Shatsky, V.S., 1990. Diamond inclusions in garnets from metamorphic
rocks: a new environment for diamond formation. Nature 343, 742.
Stachel, T., Harris, J.W., Brey, G.P., 1998. Rare and unusual mineral inclusions in diamonds
from Mwadui, Tanzania. Contributions to Mineralogy and Petrology 132, 34-47.
Stachel, T., Harris, J.W., Brey, G.P., Joswig, W., 2000. Kankan diamonds (Guinea) II: lower
mantle inclusion parageneses. Contributions to Mineralogy and Petrology 140, 16-27.
Staudigel, H., 2014. Chemical fluxes from hydrothermal alteration of the oceanic crust, in:Turekian, K.K., Holland, H. D. (Ed.), Treatise on Geochemistry (Second Edition). Elsevier, Oxford,
pp. 583-606.
Yaxley, G.M., Crawford, A.J., Green, D.H., 1991. Evidence for carbonatite metasomatismin spinel peridotite xenoliths from western Victoria, Australia. Earth Planet Sc Lett 107, 305-317.
Zedgenizov, D.A., Kagi, H., Shatsky, V.S., Ragozin, A.L., 2014a. Local variations of carbon
isotope composition in diamonds from São-Luis (Brazil): Evidence for heterogenous carbon
reservoir in sublithospheric mantle. Chemical Geology 363, 114-124.

Zedgenizov, D.A., Shatskiy, A., Ragozin, A.L., Kagi, H., Shatsky, V.S., 2014b. Merwinite
in diamond from Sao Luiz, Brazil: A new mineral of the Ca-rich mantle environment. American
Mineralogist 99, 547-550.