Geobarometric evidence for a LM/TZ origin of CaSiO3 in a sublithospheric diamond
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Keywords: super-deep diamonds, inclusions, CaSiO3, breyite, single crystal X-ray diffraction, geobarometry
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Abstract
Figures and Tables
 Figure 1 (a) Overview of the front of diamond JU55 of this work. The black square shows the location of the breyite inclusion 2, while the larger white square shows two groups of colourless breyite inclusions, groups 1(1) and 1(2). The white square shows inclusions 9 and 13, resulted to be the two TiO2 polymorphs (inclusion 9) rutile and anatase, and magnesite (inclusion 13). (b) Overview of the back of diamond JU55. The white squares show the locations of the ferropericlase inclusions. (c) Detailed view of the breyite inclusion 2. (d) Detailed view of inclusion 9 (black square) and 13 (white square). (e) Detailed view of the first ferropericlase inclusion. (f) Detailed view of the second ferropericlase inclusion. |  Figure 2 Phase diagram of the CaSiO3 system for inclusion 2 in JU55, where the CaSiO3 phase relations of Sagatova et al. (2021) are given as black dashed lines. The graphite-diamond phase boundary is given as a grey dashed line (Day, 2012). The geotherm was taken from Agee (1998). The 410 and 660 km discontinuities are given as grey lines. The entrapment pressures of the breyite inclusion are indicated by the red area. |  Table 1 T–P entrapment conditions for breyite in this study. The table reports the Ttrap–Ptrap data calculated at Pinc = 5.4 ± 0.6 GPa obtained from our X-ray diffraction volume data. These data were used to plot the Ttrap–Ptrap area in Figure 2. The uncertainty given for Ptrap is an estimation given by using the minimum and maximum value of Pinc to calculate Ptrap with the EosFitPinc software (Angel et al., 2017, 2022). |
| Figure 1 | Figure 2 | Table 1 |
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Introduction
Diamond and its entrapped mineral inclusions represent the deepest natural materials from Earth’s interior. The stability field for diamond in Earth, determined by laboratory experiments, ranges from about 150 km down to a depth of 2900 km (Maeda et al., 2017
Maeda, F., Ohtani, E., Kamada, S., Sakamaki, T., Hirao, N., Ohishi, Y. (2017) Diamond formation in the deep lower mantle: a high-pressure reaction of MgCO3 and SiO2. Scientific Reports 7, 40602. https://doi.org/10.1038/srep40602
). Diamond often encloses surrounding mantle minerals during growth (e.g., Stachel, 2001Stachel, T. (2001) Diamonds from the asthenosphere and the transition zone. European Journal of Mineralogy 13, 883–892. https://doi.org/10.1127/0935-1221/2001/0013-0883
; Brenker et al., 2007Brenker, F.E., Vollmer, C., Vincze, L., Vekemans, B., Szymanski, A., Janssens, K., Szaloki, I., Nasdala, L., Joswig, W., Kaminsky, F. (2007) Carbonates from the lower part of transition or even the lower mantle. Earth and Planetary Science Letters 260, 1–9. https://doi.org/10.1016/j.epsl.2007.02.038
; Stachel and Harris, 2009Stachel, T., Harris, J.W. (2009) Formation of diamond in the Earth’s mantle. Journal of Physics: Condensed Matter 21, 364206. http://doi.org/10.1088/0953-8984/21/36/364206
; Bulanova et al., 2010Bulanova, 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 to Mineralogy and Petrology 160, 489–510. https://doi.org/10.1007/s00410-010-0490-6
), providing an exceptional window into the Earth’s deep interior. A rare category of diamonds (Stachel and Harris, 2008Stachel, T., Harris, J.W. (2008) The origin of cratonic diamonds — Constraints from mineral inclusions. Ore Geology Reviews 34, 5–32. https://doi.org/10.1016/j.oregeorev.2007.05.002
), the so-called super-deep diamonds (or sublithospheric diamonds), are interpreted to crystallise between 300 km and a minimum of 800 km depth (Harte, 2010Harte, B. (2010) Diamond formation in the deep mantle: the record of mineral inclusions and their distribution in relation to mantle dehydration zones. Mineralogical Magazine 74, 189–215. https://doi.org/10.1180/minmag.2010.074.2.189
). This interpretation is based on mineral phases found as inclusions in these diamonds, although some are thought to be products of retrograde transformations from the transition zone or lower mantle precursors (e.g., Shirey et al., 2013Shirey, S.B., Cartigny, P., Frost, D.J., Keshav, S., Nestola, F., Nimis, P., Pearson, D.G., Sobolev, N.V., Walter, M.J. (2013) Diamonds and the Geology of Mantle Carbon. Reviews in Mineralogy and Geochemistry 75, 355–421. https://doi.org/10.2138/rmg.2013.75.12
).The Earth’s lower mantle mainly consists of ∼75–80 % bridgmanite (∼MgSiO3), 10–15 % ferropericlase [(Mg,Fe)O], and 5–10 % of a CaSiO3-phase with perovskite structure (e.g., Harte, 2010
Harte, B. (2010) Diamond formation in the deep mantle: the record of mineral inclusions and their distribution in relation to mantle dehydration zones. Mineralogical Magazine 74, 189–215. https://doi.org/10.1180/minmag.2010.074.2.189
). If these phases become trapped inside a diamond during its growth, they can be transported to the Earth’s surface without reacting kimberlite magma or ambient mantle material (e.g., Brenker et al., 2021Brenker, F.E., Nestola, F., Brenker, L., Peruzzo, L., Harris, J.W. (2021) Origin, properties, and structure of breyite: The second most abundant mineral inclusion in super-deep diamonds. American Mineralogist 106, 38–43. https://doi.org/10.2138/am-2020-7513
). During ascent, the inclusions remain chemically pristine but often transform to their lower-pressure polymorphs. However, in all other cases reported so far, a direct pressure determination that breyite (formerly called CaSiO3-walstromite) formed at lower-pressure after CaSiO3-perovskite has not been possible. After ferropericlase, breyite is the second most abundant (Brenker et al., 2021Brenker, F.E., Nestola, F., Brenker, L., Peruzzo, L., Harris, J.W. (2021) Origin, properties, and structure of breyite: The second most abundant mineral inclusion in super-deep diamonds. American Mineralogist 106, 38–43. https://doi.org/10.2138/am-2020-7513
) and the dominant Ca-bearing mineral found in super-deep diamonds (Joswig et al., 1999Joswig, W., Stachel, T., Harris, J.W., Baur, W.H., Brey, G.P. (1999) New Ca-silicate inclusions in diamonds — tracers from the lower mantle. Earth and Planetary Science Letters 173, 1–6. https://doi.org/10.1016/S0012-821X(99)00210-1
). The CaSiO3-phases are amenable to hosting elements such as Nd, Sr, U and Pb that allow radiometric dating and tracer isotopic studies. Therefore, constraining the ultimate depth of origin of CaSiO3-inclusions is critical to understanding the geochemical information coming from these studies.When breyite is simply considered to be the product of back-transformation from CaSiO3-perovskite, it would be derived from a high-pressure assemblage of peridotitic/eclogitic mantle rocks at depths below 520 km (Kaminsky, 2012
Kaminsky, F. (2012) Mineralogy of the lower mantle: A review of ‘super-deep’ mineral inclusions in diamond. Earth-Science Reviews 110, 127–147. https://doi.org/10.1016/j.earscirev.2011.10.005
; Anzolini et al., 2018Anzolini, C., Prencipe, M., Alvaro, M., Romano, C., Vona, A., Lorenzon, S., Smith, E.M., Brenker, F.E., Nestola, F. (2018) Depth of formation of super-deep diamonds: Raman barometry of CaSiO3-walstromite inclusions. American Mineralogist 103, 69–74. https://doi.org/10.2138/am-2018-6184
). However, there are indications that breyite can also be a primary inclusion phase originating from much shallower depths within the upper mantle (Anzolini et al., 2016Anzolini, C., Angel, R.J., Merlini, M., Derzsi, M., Tokár, K., Milani, S., Krebs, M.Y., Brenker, F.E., Nestola, F., Harris, J.W. (2016) Depth of formation of CaSiO3-walstromite included in super-deep diamonds. Lithos 265, 138–147. https://doi.org/10.1016/j.lithos.2016.09.025
; Thomson et al., 2016Thomson, A.R., Walter, M.J., Kohn, S.C., Brooker, R.A. (2016) Slab melting as a barrier to deep carbon subduction. Nature 529, 76–79. https://doi.org/10.1038/nature16174
). Recently, Brenker et al. (2021)Brenker, F.E., Nestola, F., Brenker, L., Peruzzo, L., Harris, J.W. (2021) Origin, properties, and structure of breyite: The second most abundant mineral inclusion in super-deep diamonds. American Mineralogist 106, 38–43. https://doi.org/10.2138/am-2020-7513
summarised possible formation scenarios for breyite that do not necessarily require great depths and showed that breyite formation is possible within the upper mantle as well. Thus, the abundance of breyite as an inclusion in sublithospheric diamonds makes determining its primary or retrograde mineral history essential in understanding mantle dynamics.Breyite formation via exsolution from a CaSiO3-CaTiO3-perovskite solid solution only requires pressures below 10 GPa, corresponding to depths of 270–300 km within the upper mantle, shown experimentally (Kubo et al., 1997
Kubo, A., Suzuki, T., Akaogi, M. (1997) High pressure phase equilibria in the system CaTiO3-CaSiO3: stability of perovskite solid solutions. Physics and Chemistry of Minerals 24, 488–494. https://doi.org/10.1007/s002690050063
) and through natural intergrowths between the two phases (e.g., Bulanova et al., 2010Bulanova, 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 to Mineralogy and Petrology 160, 489–510. https://doi.org/10.1007/s00410-010-0490-6
; Zedgenizov et al., 2016Zedgenizov, D.A., Ragozin, A.L., Kalinina, V.V., Kagi, H. (2016) The mineralogy of Ca-rich inclusions in sublithospheric diamonds. Geochemistry International 54, 890–900. https://doi.org/10.1134/S0016702916100116
). Further, breyite can form as a product of the retrograde reaction of larnite (β-Ca2SiO4) and titanite-structured CaSi2O5 at pressures between 9 and 10 GPa at depths not greater than 270–300 km (Brenker et al., 2005Brenker, F.E., Vincze, L., Vekemans, B., Nasdala, L., Stachel, T., Vollmer, C., Kersten, M., Somogyi, A., Adams, F., Joswig, W., Harris, J.W. (2005) Detection of a Ca-rich lithology in the Earth’s deep (>300 km) convecting mantle. Earth and Planetary Science Letters 236, 579–587. https://doi.org/10.1016/j.epsl.2005.05.021
; Anzolini et al., 2016Anzolini, C., Angel, R.J., Merlini, M., Derzsi, M., Tokár, K., Milani, S., Krebs, M.Y., Brenker, F.E., Nestola, F., Harris, J.W. (2016) Depth of formation of CaSiO3-walstromite included in super-deep diamonds. Lithos 265, 138–147. https://doi.org/10.1016/j.lithos.2016.09.025
, 2018Anzolini, C., Prencipe, M., Alvaro, M., Romano, C., Vona, A., Lorenzon, S., Smith, E.M., Brenker, F.E., Nestola, F. (2018) Depth of formation of super-deep diamonds: Raman barometry of CaSiO3-walstromite inclusions. American Mineralogist 103, 69–74. https://doi.org/10.2138/am-2018-6184
). The reaction of carbonate and a Si-rich component can also lead to breyite formation (Brenker et al., 2005Brenker, F.E., Vincze, L., Vekemans, B., Nasdala, L., Stachel, T., Vollmer, C., Kersten, M., Somogyi, A., Adams, F., Joswig, W., Harris, J.W. (2005) Detection of a Ca-rich lithology in the Earth’s deep (>300 km) convecting mantle. Earth and Planetary Science Letters 236, 579–587. https://doi.org/10.1016/j.epsl.2005.05.021
, 2007Brenker, F.E., Vollmer, C., Vincze, L., Vekemans, B., Szymanski, A., Janssens, K., Szaloki, I., Nasdala, L., Joswig, W., Kaminsky, F. (2007) Carbonates from the lower part of transition or even the lower mantle. Earth and Planetary Science Letters 260, 1–9. https://doi.org/10.1016/j.epsl.2007.02.038
). For this last scenario, two different pressure estimates were postulated: one at very low pressures of about 6 GPa or less (Fedoraeva et al., 2019Fedoraeva, A.S., Shatskiy, A., Litasov, K.D. (2019) The join CaCO3-CaSiO3 at 6 GPa with implication to Ca-rich lithologies trapped by kimberlitic diamonds. High Pressure Research 39, 547–560. https://doi.org/10.1080/08957959.2019.1660325
) under SiO2-poor conditions, and another at a maximum pressure of about 6–8 GPa (Woodland et al., 2020Woodland, A.B., Girnis, A.V., Bulatov, V.K., Brey, G.P., Höfer, H.E. (2020) Breyite inclusions in diamond: experimental evidence for possible dual origin. European Journal of Mineralogy 32, 171–185. https://doi.org/10.5194/ejm-32-171-2020
) in SiO2-enriched environments.These different formation mechanisms show that the sole occurrence of breyite in a diamond cannot be used as a stand-alone criterion to propose its depth of origin (Brenker et al., 2021
Brenker, F.E., Nestola, F., Brenker, L., Peruzzo, L., Harris, J.W. (2021) Origin, properties, and structure of breyite: The second most abundant mineral inclusion in super-deep diamonds. American Mineralogist 106, 38–43. https://doi.org/10.2138/am-2020-7513
) without other independent geobarometric determinations. It is known that diamond retains a certain pressure on its inclusions, known as “residual pressure” Pinc (or internal pressure) (see Supplementary Information; Angel et al., 2022Angel, R.J., Alvaro, M., Nestola, F. (2022) Crystallographic Methods for Non-destructive Characterization of Mineral Inclusions in Diamonds. Reviews in Mineralogy and Geochemistry 88, 257–305. https://doi.org/10.2138/rmg.2022.88.05
). By determining the residual pressure of an inclusion by single-inclusion elastic geobarometry, a minimum pressure for a given temperature of the entrapment of a mineral inclusion in its host diamond can be calculated (Angel et al., 2014Angel, R.J., Alvaro, M., Gonzalez-Platas, J. (2014) EosFit7c and a Fortran module (library) for equation of state calculations. Zeitschrift für Kristallographie - Crystalline Materials 229, 405–419. https://doi.org/10.1515/zkri-2013-1711
, 2015Angel, R.J., Alvaro, M., Nestola, F., Mazzucchelli, M.L. (2015) Diamond thermoelastic properties and implications for determining the pressure of formation of diamond-inclusion systems. Russian Geology and Geophysics 56, 211–220. https://doi.org/10.1016/j.rgg.2015.01.014
). The presence of fractures and/or cracks around the inclusions can affect and decrease the residual pressure as discussed in detail by Angel et al. (2022)Angel, R.J., Alvaro, M., Nestola, F. (2022) Crystallographic Methods for Non-destructive Characterization of Mineral Inclusions in Diamonds. Reviews in Mineralogy and Geochemistry 88, 257–305. https://doi.org/10.2138/rmg.2022.88.05
.A very reliable way to measure Pinc is by X-ray diffraction getting the unit-cell volumes of the inclusion before and after release from the host diamond (Anzolini et al., 2019
Anzolini, C., Nestola, F., Mazzucchelli, M.L., Alvaro, M., Nimis, P., Gianese, A., Morganti, S., Marone, F., Campione, M., Hutchison, M.T., Harris, J.W. (2019) Depth of diamond formation obtained from single periclase inclusions. Geology 47, 219–222. https://doi.org/10.1130/G45605.1
) or by comparison to a second, stand-alone reference sample of the inclusion mineral. Using this approach, we present the highest residual pressure ever measured for a breyite-diamond pair, which allows us to constrain the origin and geological implications of this super-deep diamond.top
Results
Entrapment pressure of breyite. Single-crystal X-ray diffraction (SCXRD) measurement resulted in the following unit-cell parameters for JU55 inclusion 2 (Fig. 1a, inclusion in the black square): a = 6.31(3) Å, b = 6.60(1) Å, c = 9.24(3) Å, α = 84.3(2)°, β = 71.8(3)°, γ = 77.38(3)°, and V = 356(2) Å3. This unit-cell volume was used to calculate the residual pressure (Pinc) using the EoSFit7c software (Angel et al., 2014
Angel, R.J., Alvaro, M., Gonzalez-Platas, J. (2014) EosFit7c and a Fortran module (library) for equation of state calculations. Zeitschrift für Kristallographie - Crystalline Materials 229, 405–419. https://doi.org/10.1515/zkri-2013-1711
) and the equation of state of breyite published by Anzolini et al. (2016)Anzolini, C., Angel, R.J., Merlini, M., Derzsi, M., Tokár, K., Milani, S., Krebs, M.Y., Brenker, F.E., Nestola, F., Harris, J.W. (2016) Depth of formation of CaSiO3-walstromite included in super-deep diamonds. Lithos 265, 138–147. https://doi.org/10.1016/j.lithos.2016.09.025
. This was possible comparing our unit-cell volume with that of the holotype breyite (Brenker et al., 2021Brenker, F.E., Nestola, F., Brenker, L., Peruzzo, L., Harris, J.W. (2021) Origin, properties, and structure of breyite: The second most abundant mineral inclusion in super-deep diamonds. American Mineralogist 106, 38–43. https://doi.org/10.2138/am-2020-7513
), which was measured using exactly the same instrumental set-up used in this work. The room pressure volume determined in Brenker et al. (2021)Brenker, F.E., Nestola, F., Brenker, L., Peruzzo, L., Harris, J.W. (2021) Origin, properties, and structure of breyite: The second most abundant mineral inclusion in super-deep diamonds. American Mineralogist 106, 38–43. https://doi.org/10.2138/am-2020-7513
was 376.72(4) Å3. Comparing this volume with our volume determination and using the P–V equation of state of breyite (Anzolini et al., 2016Anzolini, C., Angel, R.J., Merlini, M., Derzsi, M., Tokár, K., Milani, S., Krebs, M.Y., Brenker, F.E., Nestola, F., Harris, J.W. (2016) Depth of formation of CaSiO3-walstromite included in super-deep diamonds. Lithos 265, 138–147. https://doi.org/10.1016/j.lithos.2016.09.025
), we obtained a residual pressure Pinc value of 5.4 ± 0.6 GPa. This is the highest residual pressure ever stored in a diamond existing at Earth’s surface in a single-phase breyite inclusion. Using this Pinc along with the thermo-elastic properties of breyite (Anzolini et al., 2016Anzolini, C., Angel, R.J., Merlini, M., Derzsi, M., Tokár, K., Milani, S., Krebs, M.Y., Brenker, F.E., Nestola, F., Harris, J.W. (2016) Depth of formation of CaSiO3-walstromite included in super-deep diamonds. Lithos 265, 138–147. https://doi.org/10.1016/j.lithos.2016.09.025
), of diamond (Angel et al., 2015Angel, R.J., Alvaro, M., Nestola, F., Mazzucchelli, M.L. (2015) Diamond thermoelastic properties and implications for determining the pressure of formation of diamond-inclusion systems. Russian Geology and Geophysics 56, 211–220. https://doi.org/10.1016/j.rgg.2015.01.014
) and the EosFit-Pinc software (Angel et al., 2017Angel, R.J., Mazzucchelli, M.L., Alvaro, M., Nestola, F. (2017) EosFit-Pinc: A simple GUI for host-inclusion elastic thermobarometry. American Mineralogist 102, 1957–1960. https://doi.org/10.2138/am-2017-6190
, 2022Angel, R.J., Alvaro, M., Nestola, F. (2022) Crystallographic Methods for Non-destructive Characterization of Mineral Inclusions in Diamonds. Reviews in Mineralogy and Geochemistry 88, 257–305. https://doi.org/10.2138/rmg.2022.88.05
), we calculated the so-called “isomekes” (see Supplementary Information), which provide the entrapment pressure (Ptrap) of the diamond-breyite pair over a temperature range from 1000 to 2000 °C (Table 1). This approach yielded a pressure of formation ranging from ∼9 ± 1 GPa (about 270 km depth) at 1000 °C to ∼10 ± 1 GPa (310 km depth) at 2000 °C. These pressures are only minimum estimates because the inclusion shows small, optically visible cracks (Fig. 1c). The uncertainty given for Ptrap only represents an estimation. The minimum and maximum variation of Ptrap was determined as a function of Pinc and its uncertainty (Table 1). The entire range of T–P entrapment conditions of our breyite is plotted in Figure 2 within the phase diagram of the CaSiO3-system. Our calculated Ttrap–Ptrap plots in the deepest possible area of the breyite stability field, close to the phase boundary between CaSi2O5-titanite and larnite (β-Ca2SiO4). At ambient mantle temperatures close to 1400–1500 °C, our calculated Ptrap (Fig. 2) definitively exceeds the breyite T–P stability field. The diamond contains further breyite inclusions [Fig. 1a; at least four colourless inclusions are visible within the largest white rectangle indicated by two groups, 1(1) and 1(2)]; however, the diffraction and micro-Raman data (see Supplementary Information) on such inclusions indicated very low residual pressure Pinc likely due to typical pervasive presence of fractures that likely led to a significant pressure release.Figure 1 (a) Overview of the front of diamond JU55 of this work. The black square shows the location of the breyite inclusion 2, while the larger white square shows two groups of colourless breyite inclusions, groups 1(1) and 1(2). The white square shows inclusions 9 and 13, resulted to be the two TiO2 polymorphs (inclusion 9) rutile and anatase, and magnesite (inclusion 13). (b) Overview of the back of diamond JU55. The white squares show the locations of the ferropericlase inclusions. (c) Detailed view of the breyite inclusion 2. (d) Detailed view of inclusion 9 (black square) and 13 (white square). (e) Detailed view of the first ferropericlase inclusion. (f) Detailed view of the second ferropericlase inclusion.
Table 1 T–P entrapment conditions for breyite in this study. The table reports the Ttrap–Ptrap data calculated at Pinc = 5.4 ± 0.6 GPa obtained from our X-ray diffraction volume data. These data were used to plot the Ttrap–Ptrap area in Figure 2. The uncertainty given for Ptrap is an estimation given by using the minimum and maximum value of Pinc to calculate Ptrap with the EosFitPinc software (Angel et al., 2017
Angel, R.J., Mazzucchelli, M.L., Alvaro, M., Nestola, F. (2017) EosFit-Pinc: A simple GUI for host-inclusion elastic thermobarometry. American Mineralogist 102, 1957–1960. https://doi.org/10.2138/am-2017-6190
, 2022Angel, R.J., Alvaro, M., Nestola, F. (2022) Crystallographic Methods for Non-destructive Characterization of Mineral Inclusions in Diamonds. Reviews in Mineralogy and Geochemistry 88, 257–305. https://doi.org/10.2138/rmg.2022.88.05
).| Ttrap (°C) | Ptrap (GPa) for Pinc = 5.4 ± 0.6 GPa |
| 1000 | 8.9 |
| 1100 | 9.1 |
| 1200 | 9.2 |
| 1300 | 9.4 |
| 1400 | 9.5 |
| 1500 | 9.7 |
| 1600 | 9.8 |
| 1700 | 9.9 |
| 1800 | 10.1 |
| 1900 | 10.2 |
| 2000 | 10.3 |
Note: the estimated uncertainty in Ptrap is ±1 GPa.
Figure 2 Phase diagram of the CaSiO3 system for inclusion 2 in JU55, where the CaSiO3 phase relations of Sagatova et al. (2021)
Sagatova, D.N., Shatskiy, A.F., Sagatov, N.E., Litasov, K.D. (2021) Phase Relations in CaSiO3 System up to 100 GPa and 2500 K. Geochemistry International 59, 791–800. https://doi.org/10.1134/S0016702921080073
are given as black dashed lines. The graphite-diamond phase boundary is given as a grey dashed line (Day, 2012Day, H.W. (2012) A revised diamond-graphite transition curve. American Mineralogist 97, 52–62. https://doi.org/10.2138/am.2011.3763
). The geotherm was taken from Agee (1998)Agee, C.B. (1998) Phase transformation and seismic structure in the upper mantle and transition zone. In: Hemley, R.J. (Ed.) Ultrahigh-Pressure Mineralogy. Reviews in Mineralogy 37, Mineralogical Society of America, Washington, D.C., De Gruyter, Berlin/Munich/Boston, 165–204. https://doi.org/10.1515/9781501509179-007
. The 410 and 660 km discontinuities are given as grey lines. The entrapment pressures of the breyite inclusion are indicated by the red area.Phase identification by optical microscopy. Optical microscopy was used to identify phases which could not be analysed by micro-Raman spectroscopy and X-ray diffraction (see Supplementary Information). Most inclusions were black and small; based on their black colour these inclusions were interpreted to be graphite. Two inclusions showed a bright metallic and typical iridescent blue colour and we interpreted them as two ferropericlases (Fig. 1e, f). Unfortunately, the extremely small size of these two inclusions did not allow us to identify them by X-ray diffraction.
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Discussion
An individual breyite inclusion in a super-deep diamond can form in the upper mantle by a variety of mechanisms, as described in Brenker et al. (2021)
Brenker, F.E., Nestola, F., Brenker, L., Peruzzo, L., Harris, J.W. (2021) Origin, properties, and structure of breyite: The second most abundant mineral inclusion in super-deep diamonds. American Mineralogist 106, 38–43. https://doi.org/10.2138/am-2020-7513
. Yet, breyite can also form as the higher-pressure polymorph of Ca-silicate perovskite encapsulated in diamond in the transition zone or lower mantle. Distinguishing between these two crystallisation scenarios is essential to better understand geochemical recycling and mantle convection across the mantle transition zone. With the direct determination of residual pressure by X-ray diffraction in the lab and the elastic geobarometric calculation tools available now for this mineral, as proposed by Anzolini et al. (2016Anzolini, C., Angel, R.J., Merlini, M., Derzsi, M., Tokár, K., Milani, S., Krebs, M.Y., Brenker, F.E., Nestola, F., Harris, J.W. (2016) Depth of formation of CaSiO3-walstromite included in super-deep diamonds. Lithos 265, 138–147. https://doi.org/10.1016/j.lithos.2016.09.025
, 2018Anzolini, C., Prencipe, M., Alvaro, M., Romano, C., Vona, A., Lorenzon, S., Smith, E.M., Brenker, F.E., Nestola, F. (2018) Depth of formation of super-deep diamonds: Raman barometry of CaSiO3-walstromite inclusions. American Mineralogist 103, 69–74. https://doi.org/10.2138/am-2018-6184
), we can more accurately estimate the minimum pressure of breyite crystallisation at depth. Our results in this study indicate that the single breyite shows extremely high entrapment pressures (Fig. 2). These entrapment pressures are too high for the maximum T–P stability field determined experimentally for breyite and are not physically possible.The logical explanation is that our breyite was formed originally as CaSiO3-perovskite, likely in the transition zone or in the lower mantle. Two iridescent inclusions, optically identified as ferropericlase but too small to confirm by other methods (Fig. 1e, f), would support this explanation because CaSiO3-perovskite + ferropericlase is a typical assemblage of the lower mantle in presence of bridgmanite and would be stable at least from a minimum depth of 450 km (Liu, 1979
Lui, L.-G. (1979) The high-pressure phase transformations of monticellite and implications for upper mantle mineralogy. Physics of the Earth and Planetary Interiors 20, 25–29. https://doi.org/10.1016/0031-9201(79)90101-8
). We interpret the absence of bridgmanite as due to the generally poor ability of diamond to capture a complete modal mineral assemblage from its host rock; this is typical in diamond crystallisation. The alternative explanation, i.e. our breyite formed as a back transformation from larnite + CaSi2O5-titanite above 11–12 GPa, can be ruled out because, at least to our knowledge, no HP–HT experimental evidence exists for larnite + CaSi2O5-titanite + ferropericlase as a stable assemblage in the upper mantle down to 410 km depth.The ability to use common minerals such as breyite, often found singly in super-deep diamonds, as a reliable pressure indicator contributes greatly to understanding the geology of the mantle transition zone and lower mantle—especially when combined with other inclusions in the same diamond. Important constraints are needed on the fate of subducted slabs, how slabs release fluids at depth, how much fluid is in this region, and even the longstanding question of material transport across the 410 and 660 km seismic discontinuities. For example, the presence of magnesite (see Supplementary Information) in diamond JU55, combined with our geobarometric determinations on breyite, provides direct evidence for the existence of carbonate at lower mantle conditions. Given the link between super-deep diamonds and subducting slabs (e.g., Shirey et al., 2021
Shirey, S.B., Wagner, L.S., Walter, M.J., Pearson, D.G., van Keken, P.E. (2021) Slab Transport of Fluids to Deep Focus Earthquake Depths—Thermal Modeling Constraints and Evidence From Diamonds. AGU Advances 2, e2020AV000304. https://doi.org/10.1029/2020AV000304
; Walter et al., 2022Walter, M.J., Thomson, A.R., Smith, E.M. (2022) Geochemistry of Silicate and Oxide Inclusions in Sublithospheric Diamonds. Reviews in Mineralogy and Geochemistry 88, 393–450. https://doi.org/10.2138/rmg.2022.88.07
), along with constraints from slab thermal modelling and phase equilibria showing the possibility of transporting carbonate to the lower mantle in the carbonated crust of subducting slabs (Walter et al., 2022Walter, M.J., Thomson, A.R., Smith, E.M. (2022) Geochemistry of Silicate and Oxide Inclusions in Sublithospheric Diamonds. Reviews in Mineralogy and Geochemistry 88, 393–450. https://doi.org/10.2138/rmg.2022.88.07
), we suggest that the breyite T–P estimates and magnesite in diamond JU55 are evidence of carbon transport to lower mantle depths.top
Acknowledgement
This study was founded by the German Science Foundation DFG (project BR 2015/36-1).
Editor: Francis McCubbin
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References
Agee, C.B. (1998) Phase transformation and seismic structure in the upper mantle and transition zone. In: Hemley, R.J. (Ed.) Ultrahigh-Pressure Mineralogy. Reviews in Mineralogy 37, Mineralogical Society of America, Washington, D.C., De Gruyter, Berlin/Munich/Boston, 165–204. https://doi.org/10.1515/9781501509179-007
Show in context The geotherm was taken from Agee (1998).
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Angel, R.J., Alvaro, M., Gonzalez-Platas, J. (2014) EosFit7c and a Fortran module (library) for equation of state calculations. Zeitschrift für Kristallographie - Crystalline Materials 229, 405–419. https://doi.org/10.1515/zkri-2013-1711
Show in context By determining the residual pressure of an inclusion by single-inclusion elastic geobarometry, a minimum pressure for a given temperature of the entrapment of a mineral inclusion in its host diamond can be calculated (Angel et al., 2014, 2015).
View in article
This unit-cell volume was used to calculate the residual pressure (Pinc) using the EoSFit7c software (Angel et al., 2014) and the equation of state of breyite published by Anzolini et al. (2016).
View in article
Angel, R.J., Alvaro, M., Nestola, F., Mazzucchelli, M.L. (2015) Diamond thermoelastic properties and implications for determining the pressure of formation of diamond-inclusion systems. Russian Geology and Geophysics 56, 211–220. https://doi.org/10.1016/j.rgg.2015.01.014
Show in context By determining the residual pressure of an inclusion by single-inclusion elastic geobarometry, a minimum pressure for a given temperature of the entrapment of a mineral inclusion in its host diamond can be calculated (Angel et al., 2014, 2015).
View in article
Using this Pinc along with the thermo-elastic properties of breyite (Anzolini et al., 2016), of diamond (Angel et al., 2015) and the EosFit-Pinc software (Angel et al., 2017, 2022), we calculated the so-called “isomekes” (see Supplementary Information), which provide the entrapment pressure (Ptrap) of the diamond-breyite pair over a temperature range from 1000 to 2000 °C (Table 1).
View in article
Angel, R.J., Mazzucchelli, M.L., Alvaro, M., Nestola, F. (2017) EosFit-Pinc: A simple GUI for host-inclusion elastic thermobarometry. American Mineralogist 102, 1957–1960. https://doi.org/10.2138/am-2017-6190
Show in context Using this Pinc along with the thermo-elastic properties of breyite (Anzolini et al., 2016), of diamond (Angel et al., 2015) and the EosFit-Pinc software (Angel et al., 2017, 2022), we calculated the so-called “isomekes” (see Supplementary Information), which provide the entrapment pressure (Ptrap) of the diamond-breyite pair over a temperature range from 1000 to 2000 °C (Table 1).
View in article
The uncertainty given for Ptrap is an estimation given by using the minimum and maximum value of Pinc to calculate Ptrap with the EosFitPinc software (Angel et al., 2017, 2022).
View in article
Angel, R.J., Alvaro, M., Nestola, F. (2022) Crystallographic Methods for Non-destructive Characterization of Mineral Inclusions in Diamonds. Reviews in Mineralogy and Geochemistry 88, 257–305. https://doi.org/10.2138/rmg.2022.88.05
Show in context It is known that diamond retains a certain pressure on its inclusions, known as “residual pressure” Pinc (or internal pressure) (see Supplementary Information; Angel et al., 2022).
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The presence of fractures and/or cracks around the inclusions can affect and decrease the residual pressure as discussed in detail by Angel et al. (2022).
View in article
Using this Pinc along with the thermo-elastic properties of breyite (Anzolini et al., 2016), of diamond (Angel et al., 2015) and the EosFit-Pinc software (Angel et al., 2017, 2022), we calculated the so-called “isomekes” (see Supplementary Information), which provide the entrapment pressure (Ptrap) of the diamond-breyite pair over a temperature range from 1000 to 2000 °C (Table 1).
View in article
The uncertainty given for Ptrap is an estimation given by using the minimum and maximum value of Pinc to calculate Ptrap with the EosFitPinc software (Angel et al., 2017, 2022).
View in article
Anzolini, C., Angel, R.J., Merlini, M., Derzsi, M., Tokár, K., Milani, S., Krebs, M.Y., Brenker, F.E., Nestola, F., Harris, J.W. (2016) Depth of formation of CaSiO3-walstromite included in super-deep diamonds. Lithos 265, 138–147. https://doi.org/10.1016/j.lithos.2016.09.025
Show in context However, there are indications that breyite can also be a primary inclusion phase originating from much shallower depths within the upper mantle (Anzolini et al., 2016; Thomson et al., 2016).
View in article
Further, breyite can form as a product of the retrograde reaction of larnite (β-Ca2SiO4) and titanite-structured CaSi2O5 at pressures between 9 and 10 GPa at depths not greater than 270–300 km (Brenker et al., 2005; Anzolini et al., 2016, 2018).
View in article
Comparing this volume with our volume determination and using the P–V equation of state of breyite (Anzolini et al., 2016), we obtained a residual pressure Pinc value of 5.4 ± 0.6 GPa.
View in article
This unit-cell volume was used to calculate the residual pressure (Pinc) using the EoSFit7c software (Angel et al., 2014) and the equation of state of breyite published by Anzolini et al. (2016).
View in article
Using this Pinc along with the thermo-elastic properties of breyite (Anzolini et al., 2016), of diamond (Angel et al., 2015) and the EosFit-Pinc software (Angel et al., 2017, 2022), we calculated the so-called “isomekes” (see Supplementary Information), which provide the entrapment pressure (Ptrap) of the diamond-breyite pair over a temperature range from 1000 to 2000 °C (Table 1).
View in article
With the direct determination of residual pressure by X-ray diffraction in the lab and the elastic geobarometric calculation tools available now for this mineral, as proposed by Anzolini et al. (2016, 2018), we can more accurately estimate the minimum pressure of breyite crystallisation at depth.
View in article
Anzolini, C., Prencipe, M., Alvaro, M., Romano, C., Vona, A., Lorenzon, S., Smith, E.M., Brenker, F.E., Nestola, F. (2018) Depth of formation of super-deep diamonds: Raman barometry of CaSiO3-walstromite inclusions. American Mineralogist 103, 69–74. https://doi.org/10.2138/am-2018-6184
Show in context When breyite is simply considered to be the product of back-transformation from CaSiO3-perovskite, it would be derived from a high-pressure assemblage of peridotitic/eclogitic mantle rocks at depths below 520 km (Kaminsky, 2012; Anzolini et al., 2018).
View in article
With the direct determination of residual pressure by X-ray diffraction in the lab and the elastic geobarometric calculation tools available now for this mineral, as proposed by Anzolini et al. (2016, 2018), we can more accurately estimate the minimum pressure of breyite crystallisation at depth.
View in article
Further, breyite can form as a product of the retrograde reaction of larnite (β-Ca2SiO4) and titanite-structured CaSi2O5 at pressures between 9 and 10 GPa at depths not greater than 270–300 km (Brenker et al., 2005; Anzolini et al., 2016, 2018).
View in article
Anzolini, C., Nestola, F., Mazzucchelli, M.L., Alvaro, M., Nimis, P., Gianese, A., Morganti, S., Marone, F., Campione, M., Hutchison, M.T., Harris, J.W. (2019) Depth of diamond formation obtained from single periclase inclusions. Geology 47, 219–222. https://doi.org/10.1130/G45605.1
Show in context A very reliable way to measure Pinc is by X-ray diffraction getting the unit-cell volumes of the inclusion before and after release from the host diamond (Anzolini et al., 2019) or by comparison to a second, stand-alone reference sample of the inclusion mineral.
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Brenker, F.E., Vincze, L., Vekemans, B., Nasdala, L., Stachel, T., Vollmer, C., Kersten, M., Somogyi, A., Adams, F., Joswig, W., Harris, J.W. (2005) Detection of a Ca-rich lithology in the Earth’s deep (>300 km) convecting mantle. Earth and Planetary Science Letters 236, 579–587. https://doi.org/10.1016/j.epsl.2005.05.021
Show in context Further, breyite can form as a product of the retrograde reaction of larnite (β-Ca2SiO4) and titanite-structured CaSi2O5 at pressures between 9 and 10 GPa at depths not greater than 270–300 km (Brenker et al., 2005; Anzolini et al., 2016, 2018).
View in article
The reaction of carbonate and a Si-rich component can also lead to breyite formation (Brenker et al., 2005, 2007).
View in article
Two iridescent inclusions, optically identified as ferropericlase but too small to confirm by other methods (Fig. 1e, f), would support this explanation because CaSiO3-perovskite + ferropericlase is a typical assemblage of the lower mantle in presence of bridgmanite and would be stable at least from a minimum depth of 450 km (Liu, 1979).
View in article
Brenker, F.E., Vollmer, C., Vincze, L., Vekemans, B., Szymanski, A., Janssens, K., Szaloki, I., Nasdala, L., Joswig, W., Kaminsky, F. (2007) Carbonates from the lower part of transition or even the lower mantle. Earth and Planetary Science Letters 260, 1–9. https://doi.org/10.1016/j.epsl.2007.02.038
Show in context Diamond often encloses surrounding mantle minerals during growth (e.g., Stachel, 2001; Brenker et al., 2007; Stachel and Harris, 2009; Bulanova et al., 2010), providing an exceptional window into the Earth’s deep interior.
View in article
The reaction of carbonate and a Si-rich component can also lead to breyite formation (Brenker et al., 2005, 2007).
View in article
Brenker, F.E., Nestola, F., Brenker, L., Peruzzo, L., Harris, J.W. (2021) Origin, properties, and structure of breyite: The second most abundant mineral inclusion in super-deep diamonds. American Mineralogist 106, 38–43. https://doi.org/10.2138/am-2020-7513
Show in context If these phases become trapped inside a diamond during its growth, they can be transported to the Earth’s surface without reacting kimberlite magma or ambient mantle material (e.g., Brenker et al., 2021).
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After ferropericlase, breyite is the second most abundant (Brenker et al., 2021) and the dominant Ca-bearing mineral found in super-deep diamonds (Joswig et al., 1999).
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Recently, Brenker et al. (2021) summarised possible formation scenarios for breyite that do not necessarily require great depths and showed that breyite formation is possible within the upper mantle as well.
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These different formation mechanisms show that the sole occurrence of breyite in a diamond cannot be used as a stand-alone criterion to propose its depth of origin (Brenker et al., 2021) without other independent geobarometric determinations.
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This was possible comparing our unit-cell volume with that of the holotype breyite (Brenker et al., 2021), which was measured using exactly the same instrumental set-up used in this work.
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The room pressure volume determined in Brenker et al. (2021) was 376.72(4) Å3
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An individual breyite inclusion in a super-deep diamond can form in the upper mantle by a variety of mechanisms, as described in Brenker et al. (2021).
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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 to Mineralogy and Petrology 160, 489–510. https://doi.org/10.1007/s00410-010-0490-6
Show in context Diamond often encloses surrounding mantle minerals during growth (e.g., Stachel, 2001; Brenker et al., 2007; Stachel and Harris, 2009; Bulanova et al., 2010), providing an exceptional window into the Earth’s deep interior.
View in article
Breyite formation via exsolution from a CaSiO3-CaTiO3-perovskite solid solution only requires pressures below 10 GPa, corresponding to depths of 270–300 km within the upper mantle, shown experimentally (Kubo et al., 1997) and through natural intergrowths between the two phases (e.g., Bulanova et al., 2010; Zedgenizov et al., 2016).
View in article
Day, H.W. (2012) A revised diamond-graphite transition curve. American Mineralogist 97, 52–62. https://doi.org/10.2138/am.2011.3763
Show in context The graphite-diamond phase boundary is given as a grey dashed line (Day, 2012).
View in article
Fedoraeva, A.S., Shatskiy, A., Litasov, K.D. (2019) The join CaCO3-CaSiO3 at 6 GPa with implication to Ca-rich lithologies trapped by kimberlitic diamonds. High Pressure Research 39, 547–560. https://doi.org/10.1080/08957959.2019.1660325
Show in context For this last scenario, two different pressure estimates were postulated: one at very low pressures of about 6 GPa or less (Fedoraeva et al., 2019) under SiO2-poor conditions, and another at a maximum pressure of about 6–8 GPa (Woodland et al., 2020) in SiO2-enriched environments.
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Harte, B. (2010) Diamond formation in the deep mantle: the record of mineral inclusions and their distribution in relation to mantle dehydration zones. Mineralogical Magazine 74, 189–215. https://doi.org/10.1180/minmag.2010.074.2.189
Show in context A rare category of diamonds (Stachel and Harris, 2008), the so-called super-deep diamonds (or sublithospheric diamonds), are interpreted to crystallise between 300 km and a minimum of 800 km depth (Harte, 2010).
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The Earth’s lower mantle mainly consists of ∼75–80 % bridgmanite (∼MgSiO3), 10–15 % ferropericlase [(Mg,Fe)O], and 5–10 % of a CaSiO3-phase with perovskite structure (e.g., Harte, 2010).
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Joswig, W., Stachel, T., Harris, J.W., Baur, W.H., Brey, G.P. (1999) New Ca-silicate inclusions in diamonds — tracers from the lower mantle. Earth and Planetary Science Letters 173, 1–6. https://doi.org/10.1016/S0012-821X(99)00210-1
Show in context After ferropericlase, breyite is the second most abundant (Brenker et al., 2021) and the dominant Ca-bearing mineral found in super-deep diamonds (Joswig et al., 1999).
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Kaminsky, F. (2012) Mineralogy of the lower mantle: A review of ‘super-deep’ mineral inclusions in diamond. Earth-Science Reviews 110, 127–147. https://doi.org/10.1016/j.earscirev.2011.10.005
Show in context When breyite is simply considered to be the product of back-transformation from CaSiO3-perovskite, it would be derived from a high-pressure assemblage of peridotitic/eclogitic mantle rocks at depths below 520 km (Kaminsky, 2012; Anzolini et al., 2018).
View in article
Kubo, A., Suzuki, T., Akaogi, M. (1997) High pressure phase equilibria in the system CaTiO3-CaSiO3: stability of perovskite solid solutions. Physics and Chemistry of Minerals 24, 488–494. https://doi.org/10.1007/s002690050063
Show in context Breyite formation via exsolution from a CaSiO3-CaTiO3-perovskite solid solution only requires pressures below 10 GPa, corresponding to depths of 270–300 km within the upper mantle, shown experimentally (Kubo et al., 1997) and through natural intergrowths between the two phases (e.g., Bulanova et al., 2010; Zedgenizov et al., 2016).
View in article
Lui, L.-G. (1979) The high-pressure phase transformations of monticellite and implications for upper mantle mineralogy. Physics of the Earth and Planetary Interiors 20, 25–29. https://doi.org/10.1016/0031-9201(79)90101-8
Show in context Two iridescent inclusions, optically identified as ferropericlase but too small to confirm by other methods (Fig. 1e, f), would support this explanation because CaSiO3-perovskite + ferropericlase is a typical assemblage of the lower mantle in presence of bridgmanite and would be stable at least from a minimum depth of 450 km (Liu, 1979).
View in article
Maeda, F., Ohtani, E., Kamada, S., Sakamaki, T., Hirao, N., Ohishi, Y. (2017) Diamond formation in the deep lower mantle: a high-pressure reaction of MgCO3 and SiO2. Scientific Reports 7, 40602. https://doi.org/10.1038/srep40602
Show in context The stability field for diamond in Earth, determined by laboratory experiments, ranges from about 150 km down to a depth of 2900 km (Maeda et al., 2017).
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Sagatova, D.N., Shatskiy, A.F., Sagatov, N.E., Litasov, K.D. (2021) Phase Relations in CaSiO3 System up to 100 GPa and 2500 K. Geochemistry International 59, 791–800. https://doi.org/10.1134/S0016702921080073
Show in context Phase diagram of the CaSiO3 system for inclusion 2 in JU55, where the CaSiO3 phase relations of Sagatova et al. (2021) are given as black dashed lines.
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Shirey, S.B., Cartigny, P., Frost, D.J., Keshav, S., Nestola, F., Nimis, P., Pearson, D.G., Sobolev, N.V., Walter, M.J. (2013) Diamonds and the Geology of Mantle Carbon. Reviews in Mineralogy and Geochemistry 75, 355–421. https://doi.org/10.2138/rmg.2013.75.12
Show in context This interpretation is based on mineral phases found as inclusions in these diamonds, although some are thought to be products of retrograde transformations from the transition zone or lower mantle precursors (e.g., Shirey et al., 2013).
View in article
Shirey, S.B., Wagner, L.S., Walter, M.J., Pearson, D.G., van Keken, P.E. (2021) Slab Transport of Fluids to Deep Focus Earthquake Depths—Thermal Modeling Constraints and Evidence From Diamonds. AGU Advances 2, e2020AV000304. https://doi.org/10.1029/2020AV000304
Show in context Given the link between super-deep diamonds and subducting slabs (e.g., Shirey et al., 2021; Walter et al., 2022), along with constraints from slab thermal modelling and phase equilibria showing the possibility of transporting carbonate to the lower mantle in the carbonated crust of subducting slabs (Walter et al., 2022), we suggest that the breyite T–P estimates and magnesite in diamond JU55 are evidence of carbon transport to lower mantle depths.
View in article
Stachel, T. (2001) Diamonds from the asthenosphere and the transition zone. European Journal of Mineralogy 13, 883–892. https://doi.org/10.1127/0935-1221/2001/0013-0883
Show in context Diamond often encloses surrounding mantle minerals during growth (e.g., Stachel, 2001; Brenker et al., 2007; Stachel and Harris, 2009; Bulanova et al., 2010), providing an exceptional window into the Earth’s deep interior.
View in article
Stachel, T., Harris, J.W. (2008) The origin of cratonic diamonds — Constraints from mineral inclusions. Ore Geology Reviews 34, 5–32. https://doi.org/10.1016/j.oregeorev.2007.05.002
Show in context A rare category of diamonds (Stachel and Harris, 2008), the so-called super-deep diamonds (or sublithospheric diamonds), are interpreted to crystallise between 300 km and a minimum of 800 km depth (Harte, 2010).
View in article
Stachel, T., Harris, J.W. (2009) Formation of diamond in the Earth’s mantle. Journal of Physics: Condensed Matter 21, 364206. http://doi.org/10.1088/0953-8984/21/36/364206
Show in context Diamond often encloses surrounding mantle minerals during growth (e.g., Stachel, 2001; Brenker et al., 2007; Stachel and Harris, 2009; Bulanova et al., 2010), providing an exceptional window into the Earth’s deep interior.
View in article
Thomson, A.R., Walter, M.J., Kohn, S.C., Brooker, R.A. (2016) Slab melting as a barrier to deep carbon subduction. Nature 529, 76–79. https://doi.org/10.1038/nature16174
Show in context However, there are indications that breyite can also be a primary inclusion phase originating from much shallower depths within the upper mantle (Anzolini et al., 2016; Thomson et al., 2016).
View in article
Walter, M.J., Thomson, A.R., Smith, E.M. (2022) Geochemistry of Silicate and Oxide Inclusions in Sublithospheric Diamonds. Reviews in Mineralogy and Geochemistry 88, 393–450. https://doi.org/10.2138/rmg.2022.88.07
Show in context Given the link between super-deep diamonds and subducting slabs (e.g., Shirey et al., 2021; Walter et al., 2022), along with constraints from slab thermal modelling and phase equilibria showing the possibility of transporting carbonate to the lower mantle in the carbonated crust of subducting slabs (Walter et al., 2022), we suggest that the breyite T–P estimates and magnesite in diamond JU55 are evidence of carbon transport to lower mantle depths.
View in article
Woodland, A.B., Girnis, A.V., Bulatov, V.K., Brey, G.P., Höfer, H.E. (2020) Breyite inclusions in diamond: experimental evidence for possible dual origin. European Journal of Mineralogy 32, 171–185. https://doi.org/10.5194/ejm-32-171-2020
Show in context For this last scenario, two different pressure estimates were postulated: one at very low pressures of about 6 GPa or less (Fedoraeva et al., 2019) under SiO2-poor conditions, and another at a maximum pressure of about 6–8 GPa (Woodland et al., 2020) in SiO2-enriched environments.
View in article
Zedgenizov, D.A., Ragozin, A.L., Kalinina, V.V., Kagi, H. (2016) The mineralogy of Ca-rich inclusions in sublithospheric diamonds. Geochemistry International 54, 890–900. https://doi.org/10.1134/S0016702916100116
Show in context Breyite formation via exsolution from a CaSiO3-CaTiO3-perovskite solid solution only requires pressures below 10 GPa, corresponding to depths of 270–300 km within the upper mantle, shown experimentally (Kubo et al., 1997) and through natural intergrowths between the two phases (e.g., Bulanova et al., 2010; Zedgenizov et al., 2016).
View in article
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Supplementary Information
The Supplementary Information includes:
- Material and Methods
- Figures S-1 to S-3
- Supplementary Information References
Download the Supplementary Information (PDF)
Figures
Figure 1 (a) Overview of the front of diamond JU55 of this work. The black square shows the location of the breyite inclusion 2, while the larger white square shows two groups of colourless breyite inclusions, groups 1(1) and 1(2). The white square shows inclusions 9 and 13, resulted to be the two TiO2 polymorphs (inclusion 9) rutile and anatase, and magnesite (inclusion 13). (b) Overview of the back of diamond JU55. The white squares show the locations of the ferropericlase inclusions. (c) Detailed view of the breyite inclusion 2. (d) Detailed view of inclusion 9 (black square) and 13 (white square). (e) Detailed view of the first ferropericlase inclusion. (f) Detailed view of the second ferropericlase inclusion.
Figure 2 Phase diagram of the CaSiO3 system for inclusion 2 in JU55, where the CaSiO3 phase relations of Sagatova et al. (2021)
Sagatova, D.N., Shatskiy, A.F., Sagatov, N.E., Litasov, K.D. (2021) Phase Relations in CaSiO3 System up to 100 GPa and 2500 K. Geochemistry International 59, 791–800. https://doi.org/10.1134/S0016702921080073
are given as black dashed lines. The graphite-diamond phase boundary is given as a grey dashed line (Day, 2012Day, H.W. (2012) A revised diamond-graphite transition curve. American Mineralogist 97, 52–62. https://doi.org/10.2138/am.2011.3763
). The geotherm was taken from Agee (1998)Agee, C.B. (1998) Phase transformation and seismic structure in the upper mantle and transition zone. In: Hemley, R.J. (Ed.) Ultrahigh-Pressure Mineralogy. Reviews in Mineralogy 37, Mineralogical Society of America, Washington, D.C., De Gruyter, Berlin/Munich/Boston, 165–204. https://doi.org/10.1515/9781501509179-007
. The 410 and 660 km discontinuities are given as grey lines. The entrapment pressures of the breyite inclusion are indicated by the red area.