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Carbonation and melting reactions in the system CaO–MgO–SiO2–CO2 at mantle pressures with geophysical and petrological applications


Bowen's petrogenetic grid was based initially on a series of decarbonation reactions in the system CaO-MgO-SiO2-CO2 with starting assemblages including calcite, dolomite, magnesite and quartz, and products including enstatite, forsterite, diopside and wollastonite. We review the positions of 14 decarbonation reactions, experimentally determined or estimated, extending the grid to mantle pressures to evaluate the effect of CO2 on model mantle peridotite composed of forsterite(Fo)+orthopyroxene(Opx)+clinopyroxene(Cpx). Each reaction terminates at an invariant point involving a liquid, CO2, carbonates, and silicates. The fusion curves for the mantle mineral assemblages in the presence of excess CO2 also terminate at these invariant points. The points are connected by a series of reactions involving liquidus relationships among the carbonates and mantle silicates, at temperatures lower (1,100–1,300° C) than the silicate-CO2 melting reactions (1,400–1,600° C). Review of experimental data in the bounding ternary systems together with preliminary data for the system CaO-MgO-SiO2-CO2 permits construction of a partly schematic framework for decarbonation and melting reactions at upper mantle pressures. The key to several problems in the peridotite-CO2 subsystem is the intersection of a subsolidus carbonation reaction with a melting reaction at an invariant point near 24 kb and 1,200°C. There is an intricate series of reactions between 25 kb and 35 kb involving changes in silicate and carbonate phase fields on the CO2-saturated liquidus surfaces. Conclusions include the following: (1) Peridotite Fo+Opx+Cpx can be carbonated with increasing pressure, or decreasing temperature, to yield Fo+Opx+Cpx+Cd (Cd=calcic dolomite), Fo+Opx+Cd, Fo+Opx+Cm (Cm=calcic magnesite), and finally Qz+Cm. (2) Free CO2 cannot exist in subsolidus mantle peridotite with normal temperature distributions; it is stored as carbonate, Cd. (3) The CO2 bubbles in peridotite nodules do not represent free CO2 in mantle peridotite along normal geotherms. (4) CO2 is as effective as H2O in causing incipient melting, our preferred explanation for the low-velocity zone. (5) Fusion of peridotite with CO2 at depths shallower than 80 km produces basic magmas, becoming more SiO2-undersaturated with depth. (6) The solubility of CO2 in mantle magmas is less than about 5 wt% at depths to 80 km, increasing abruptly to about 40 wt% at 80 km and deeper. (7) Deeper than 80 km, the first liquids produced are carbonatitic, changing towards kimberlitic and eventually, at considerably higher temperatures, to basic magmas. (8) Kimberlite and carbonatite magmas rising from the asthenosphere must evolve CO2 at depths 100-80 km, which contributes to their explosive emplacement. (9) Fractional crystallization of CO2-bearing SiO2-undersaturated basic magmas at most pressures can yield residual kimberlite and carbonatite magmas.

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  1. 1.

    Boettcher, A.L.: Experimental igneous petrology. Rev. Geophys. Space Phys. 13, 75–79 (1975)

    Google Scholar 

  2. 2.

    Wyllie, P.J., Boettcher, A.L.: Liquidus phase relationships in the system CaO-CO2-H2O to 40 kilobars pressure with petrological applications. Am. J. Sci. 267A, 489–508 (1969)

    Google Scholar 

  3. 3.

    Boettcher, A.L., Wyllie, P.J.: The system CaO-SiO2-CO2-H2O, III. Second critical end-point on the melting curve. Geochim. Cosmochim. Acta 33, 611–632 (1969)

    Google Scholar 

  4. 4.

    Franz, G.W.: Melting relationships in the system CaO-MgO-SiO2-CO2-H2O: a study of synthetic kimberlites. Ph.D. thesis, The Pennsylvania State University

  5. 5.

    Franz, G.W., Wyllie, P.J.: Experimental studies in the system CaO-MgO-SiO2-CO2-H2O. In: Ultramafic and related rocks, P.J. Wyllie, ed., p. 323–325. New York: John Wiley 1967

    Google Scholar 

  6. 6.

    Wyllie, P.J.: Experimental studies of carbonatite problems: the origin and differentiation of carbonatite magmas. In: Carbonatites, O.F. Tuttle, J. Gittins, eds., p. 311–352. New York: John Wiley 1966

    Google Scholar 

  7. 7.

    Koster van Groos, A.F., Wyllie, P.J.: Liquid immiscibility in the join NaAlSi3O8-CaAl2Si2O8-Na2CO3-H2O. Am. J. Sci. 273, 465–487 (1973)

    Google Scholar 

  8. 8.

    Irving, A.J., Wyllie, P.J.: Melting relationships in CaO-CO2 and MgO-CO2 to 36 kilobars with comments on CO2 in the mantle. Earth Planet. Sci. Lett. 20, 220–225 (1973)

    Google Scholar 

  9. 9.

    Irving, A.J., Wyllie, P.J.: Subsolidus and melting relationships for calcite, magnesite and the join CaCO3-MgCO3 to 36 kb. Geochim. Cosmochim. Acta 39, 35–53 (1975)

    Google Scholar 

  10. 10.

    Huang, W.L., Wyllie, P.J.: Melting relationships in the systems CaO-CO2 and MgO-CO2 to 33 kilobars. Geochim. Cosmochim. Acta (in press, 1975)

  11. 11.

    Huang, W.L., Wyllie, P.J.: Eutectic between wollastonite II and calcite contrasted with thermal barrier in MgO-SiO2-CO2 at 30 kilobars, with applications to kimberlite-carbonatite petrogenesis. Earth Planet. Sci. Lett. 24, 305–310 (1974)

    Google Scholar 

  12. 12.

    Maaløe, S., Wyllie, P.J.: The join grossularite-calcite through the system CaO-Al2O3-SiO2- CO2 at 30 kilobars: crystallization range of silicates and carbonates on the liquidus. Earth Planet. Sci. Lett. (in press, 1975)

  13. 13.

    Yoder, H.S.: Relationship of melilite-bearing rocks to kimberlite: a preliminary report on the system akermanite-CO2. In: Physics and chemistry of the earth, L.H. Ahrens, J.B. Dawson, A.R. Duncan, A.J. Erlank, eds., vol. 9. Oxford: Pergamon Press 1975

    Google Scholar 

  14. 14.

    Eggler, D.H.: Carbonatite generation by a reaction relation in the system CaO-MgO-SiO2-CO2 at 30 kbar pressure (Abstr). Trans. Am. Geophys. Union 56, 470 (1975)

    Google Scholar 

  15. 15.

    Bowen, N.L.: Progressive metamorphism of siliceous limestone and dolomite. J. Geol. 48, 225–274 (1940)

    Google Scholar 

  16. 16.

    Turner, F.J.: Metamorphic petrology. 403 p. New York: McGraw-Hill 1968

    Google Scholar 

  17. 17.

    Skippen, G.: An experimental model for low pressure metamorphism of siliceous dolomitic marble. Am. J. Sci. 274, 487–509 (1974)

    Google Scholar 

  18. 18.

    Kerrick, D.M.: Review of metamorphic mixed volatile (H2O-CO2) equilibria. Am. Mineralogist 59, 729–762 (1974)

    Google Scholar 

  19. 19.

    Huang, W.L., Wyllie, P.J., Nehru, C.E.: Subsolidus and melting relationships in the system CaO-SiO2-CO2 to 30 kb with geological applications. Manuscript to be submitted to Geochim. Cosmochim. Acta

  20. 20.

    Schreinemakers, F.A.H.: In-, mono- and divariant equilibria. Amsterdam Acad. Sci. Proc. 18, 820–828 (1916)

    Google Scholar 

  21. 21.

    Huang, W.L., Wyllie, P.J.: Melting and subsolidus phase relationships for CaSiO3 to 35 kilobars pressure. Am. Mineralogist 60, 213–217 (1975)

    Google Scholar 

  22. 22.

    Eggler, D.H., Mysen, B.O., Seitz, M.G.: Solubility of CO2 in silicate liquids and crystals. Carnegie Inst. Wash. Yearb. 73, 226–228 (1974)

    Google Scholar 

  23. 23.

    Newton, R.C., Sharp, W.E.: Stability of forsterite + CO2 and its bearing on the role of CO2 in the mantle. Earth Planet. Sci. Lett. 26, 239–244 (1975)

    Google Scholar 

  24. 24.

    Eggler, D.H.: CO2 as a volatile component of the mantle: the system Mg2SiO4-SiO2-H2O-CO2. In: Physics and chemistry of the earth, L.H. Arhens, J.B. Dawson, A.R. Duncan, and A.J. Erlank, eds., vol. 9. Oxford: Pergamon Press 1975

    Google Scholar 

  25. 25.

    Eggler, D.H.: Effect of CO2 on the melting of peridotite. Carnegie Inst. Wash. Yearb. 73, 215–224 (1974)

    Google Scholar 

  26. 26.

    Davis, B.T.C., Boyd, F.R.: The join Mg2Si2O6-CaMgSi2O6 at 30 kilobars pressure and its application to pyroxenes from kimberlites. J. Geophys. Res. 71, 3567–3576 (1966)

    Google Scholar 

  27. 27.

    Nehru, C.E., Wyllie, P.J.: Electron microprobe measurement of pyroxenes coexisting with H2O-undersaturated liquid in the join CaMgSi2O6-Mg2Si2O6-H2O at 30 kilobars, with applications to geothermometry. Contrib. Mineral. Petrol. 48, 221–228 (1974)

    Google Scholar 

  28. 28.

    Muan, A., Osborn, E.F.: Phase equilibria among oxides in steelmaking. Reading, Massachusetts: Addison-Wesley 1965.

    Google Scholar 

  29. 29.

    Kushiro, I., Schairer, J.F.: New data on the system diopside-forsterite-silica. Carnegie Inst. Wash. Yearb. 62, 95–103 (1963)

    Google Scholar 

  30. 30.

    Kushiro, I.: Effect of water on the composition of magmas formed at high pressures. J. Petrol. 13, 311–334 (1972)

    Google Scholar 

  31. 31.

    Yoder, H.S.: Akermanite and related melilite-bearing assemblages. Carnegie Inst. Wash. Yearb. 66, 471–477 (1968)

    Google Scholar 

  32. 32.

    Kushiro, I., Yoder, H.S.: Breakdown of monticellite and akermanite at high pressures. Carnegie Inst. Wash. Yearb. 63, 81–83

  33. 33.

    Huang, W.L., Wyllie, P.J.: Liquidus relationships between carbonates and silicates in parts of the system CaO-MgO-SiO2-H2O at 30 kb (Abstr). Eos, Trans. Am. Geophys. Union 55, 479–480 (1974)

    Google Scholar 

  34. 34.

    Modreski, P.J., Boettcher, A.L.: Phase relationships of phlogopite in the system K2O-MgO-CaO-A12O3-SiO2-H2O to 35 kilobars: a better model for micas in the interior of the earth. Am. J. Sci. 273, 385–414 (1973)

    Google Scholar 

  35. 35.

    Clark, S.P., Ringwood, A.E.: Density distribution and constitution of the mantle. Rev. Geophysics 2, 35–88 (1964)

    Google Scholar 

  36. 36.

    Ringwood, A.E.: Mineralogy of the mantle. In: Advances in earth sciences, P.M. Hurley, ed., p. 357–399. Cambridge, Massachusetts: M.I.T. Press 1966

    Google Scholar 

  37. 37.

    Koster van Groos, A.F.: The effect of high CO2 pressures on alkalic rock and its bearing on the formation of alkalic ultrabasic rocks and the associated carbonatites. Am. J. Sci. 275, 163–185 (1975)

    Google Scholar 

  38. 38.

    Newton, R.C., Goldsmith, J.R.: Stability of the scapolite meionite (3CaAl2Si2O8-CaCO3) at high pressures and storage of CO2 in the deep crust. Contrib. Mineral. Petrol. 49, 49–62 (1975)

    Google Scholar 

  39. 39.

    Roedder, E.: Liquid CO2 inclusions in olivine-bearing nodules and phenocrysts in basalts. Am. Mineralogist 50, 1746–1782 (1965)

    Google Scholar 

  40. 40.

    Green, H.W. II: A CO2 charged asthenosphere. Nature Phys. Sci. 238, 2–5 (1972)

    Google Scholar 

  41. 41.

    Kennedy, G.D., Nordlie, B.E.: The genesis of diamond deposits. Econ. Geol. 63, 495–503 (1968)

    Google Scholar 

  42. 42.

    Wyllie, P.J.: Role of water in magma generation and initiation of diapiric uprise in the mantle. J. Geophys. Res. 76, 1328–1338 (1971)

    Google Scholar 

  43. 43.

    Millhollen, G.L., Irving, A.J., Wyllie, P.J.: Melting interval of peridotite with 5.7 per cent water to 30 kilobars. J. Geol. 82, 575–587 (1974)

    Google Scholar 

  44. 44.

    Boettcher, A.L., Mysen, B.O., Modreski, P.J.: Melting in the mantle: phase relationships in natural and synthetic peridotite-H2O and peridotite-H2O-CO2 at high pressures. In: Physics and chemistry of the earth, L.H. Ahrens, F. Press, S.K. Runcorn, H.C. Urey, eds., vol. 9, p. 855–867. Oxford: Pergamon Press 1975

    Google Scholar 

  45. 45.

    Lambert, I.B., Wyllie, P.J.: Stability of hornblende and a model for the low velocity zone. Nature 219, 1240–1241 (1968)

    Google Scholar 

  46. 46.

    Lambert, I.B., Wyllie, P.J.: Low-velocity zone of the earth's mantle: incipient melting caused by water. Science 169, 764–766 (1970)

    Google Scholar 

  47. 47.

    Green, H.W., Radcliffe, S.V.: Fluid precipitates in rocks from the earth's mantle. Geol. Soc. Am. Bull. 86, 846–852 (1975)

    Google Scholar 

  48. 48.

    Morey, G.W., Fleischer, M.: Equilibrium between vapor and liquid phases in the system CO2-H2O-K2O-SiO2. Geol. Soc. Am. Bull. 51, 1035–1058 (1940)

    Google Scholar 

  49. 49.

    Koster van Groos, A.F., Wyllie, P.J.: Liquid immiscibility in the system Na2O-A12O3-SiO2-CO2 at pressures up to 1 kilobar. Am. J. Sci. 264, 234–255 (1966)

    Google Scholar 

  50. 50.

    Wyllie, P.J., Tuttle, O.F.: Effect of carbon dioxide on the melting of granite and feldspars. Am. J. Sci. 257, 648–655 (1959)

    Google Scholar 

  51. 51.

    Holloway, J.R., Burnham, C.W.: Melting relations of basalt with equilibrium water pressure less than total pressure. J. Petrol. 13, 1–29 (1972)

    Google Scholar 

  52. 52.

    Eggler, D.H., Burnham, C.W.: Crystallization and fractionation trends in the system andesite-H2O-CO2-O2 at pressures to 10 kb. Geol. Soc. Am. Bull. 84, 2517–2532 (1973)

    Google Scholar 

  53. 53.

    Hill, R.E.T., Boettcher, A.L.: Water in the earth's mantle: melting curves of basalt-water-carbon dioxide. Science 167, 980–982 (1970)

    Google Scholar 

  54. 54.

    Millhollen, G.L., Wyllie, P.J., Burnham, C.W.: Melting relations of NaAlSi3O8 to 30 kb in the presence of H2O∶ CO2=50∶ 50 vapor. Am. J. Sci. 271, 473–480 (1971)

    Google Scholar 

  55. 55.

    Eggler, D.H.: Role of CO2 in melting processes in the mantle. Carnegie Inst. Wash. Yearb. 72, 457–467 (1973)

    Google Scholar 

  56. 56.

    Brey, G., Green, D.H.: The role of CO2 in the genesis of olivine melilitite. Contrib. Mineral. Petrol. 49, 93–103 (1975)

    Google Scholar 

  57. 57.

    Boyd, F.R.: A pyroxene geotherm. Geochim. Cosmochim. Acta 37, 2533–2546 (1973)

    Google Scholar 

  58. 58.

    MacGregor, I.D.: The system MgO-A12O3-SiO2: solubility of Al2O3 in enstatite for spinel and garnet peridotite compositions. Am. Mineralogist 59, 110–119 (1974)

    Google Scholar 

  59. 59.

    Mercier, J.-C., Carter, N.L.: Pyroxene geotherms. J. Geophys. Res. 80, 3349–3362 (1975)

    Google Scholar 

  60. 60.

    McGetchin, T.R., Besancon, J.R.: Carbonate inclusions in mantle-derived pyropes. Earth Planet. Sci. Lett. 18, 408–410 (1973)

    Google Scholar 

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Wyllie, P.J., Huang, W.L. Carbonation and melting reactions in the system CaO–MgO–SiO2–CO2 at mantle pressures with geophysical and petrological applications. Contr. Mineral. and Petrol. 54, 79–107 (1976).

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  • Magnesite
  • Forsterite
  • Wollastonite
  • Asthenosphere
  • Enstatite