Contributions to Mineralogy and Petrology

, Volume 85, Issue 4, pp 391–403 | Cite as

Equilibrium state of diopside-bearing harzburgites from ophiolites: Geobarometric and geodynamic implications

  • Jean -Claude C. Mercier
  • Vincent Benoit
  • Jacques Girardeau


The bulk compositions of coexisting enstatite and diopside in basal lherzolites and clinopyroxene-bearing harzburgites from ophiolitic complexes are typical of solidus/subsolidus equilibria, but for a few texturally distinct “magmatic” diopsides. They would presumably reflect the state of equilibrium at the time they last coexisted with liquid as the rocks reentered subsolidus conditions. The total lack of correlation between Al and Ca concentrations shows that the compositional scatter observed for any given massif, results from analytical errors related to extensive exsolution and serpentinization, rather than from differences in equilibrium conditions. However, significant differences are found between the residual ophiolitic lherzolites from Hare Bay, Newfoundland, and from Xigaze, Tibet, two massifs selected for their distinct structural and textural features. As for thermobarometry techniques relevant to these rocks, the best barometer found is an empirical relation for the expression of pressure as a virtually temperature-independent function of the ratioKf=(X Di opx )/(1 −X Di cpx ), in agreement with semi-quantitative models based on natural solid solutions. Temperatures are then simply derived from a surface-fitting expression relating pressure, temperature and diopside-solvus compositions, according to a regularX En cpx solution model (CMS) corrected for the effect of Al in the spinel facies. Application of these techniques yield pressures of 0.4 and 1.4 GPa, i.e. depths from sea-bottom of about 13 and 43 km, for temperatures of 1,170 and 1,300° C for the ophiolitic lherzolites of Tibet and New-foundland, respectively, in good agreement with dry-solidus data by radioactive tracing and with geothermal-model estimates for ridges.


Analytical Error Textural Feature Solution Model Diopside Empirical Relation 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Akella J (1976) Garnet-pyroxene equilibria in the system CaSiO3-MgSiO3-Al2O3 and in a natural mineral mixture. Am Mineral 61:589–598Google Scholar
  2. Avé Lallemant HG, Mercier JCC, Ross JV, Carter NL (1980) Rheology of the upper mantle: inferences from peridotite xenoliths, Tectonophysics 70:85–113Google Scholar
  3. Benoit V, Mercier JCC (1982) Etat d'équilibre des pyroxenes des péridotites ophiolitiques: implications thermobarométriques. Soc Géol France: Réun Ann Sc Terre 9:44Google Scholar
  4. Benoit V, Mercier JCC (1983) Equilibrium state of pyroxenes in ophiolitic complexes: implications for geothermobarometry. Terra Cognita 3:155Google Scholar
  5. Berger E (1981) Enclaves ultramafiques, mégacristaux et leurs basaltes-hôtes en contexte océanique (Pacifique Sud) et continental (Massif Central francais). D.Sc. Thesis, Univ Paris-Sud, Orsay, France:1–470Google Scholar
  6. Bottinga Y, Allegre CJ (1976) Geophysical, petrological and geochemical models of the oceanic lithosphere. Tectonophysics 32:9–59Google Scholar
  7. Bottinga Y, Steinmetz L (1979) A geophysical, geochemical, petrological model of the sub-marine lithosphere. Tectonophysics 55:311–347Google Scholar
  8. Boyd FR, England JL (1964) The system enstatite-pyrope. Carnegie Inst Wash Yearb 63:157–161Google Scholar
  9. Brey G, Huth J (1983) The enstatite-diopside solvus to 60 kbar. Dev Petrol 257–264Google Scholar
  10. Bussod G (1982) Nature of the continental upper-mantle/lowercrust transition beneath Kilbourne Hole, New Mexico. Terra Cognita 2:266–267Google Scholar
  11. Crough ST (1975) Thermal model of the oceanic lithosphere. Nature 256:388–390Google Scholar
  12. Davidson PM, Grover JE, Lindsley DH (1982) (Ca, Mg)2Si2O6 clinopyroxenes: a solution model based on a non-convergent site disorder. Contrib Mineral Petrol 80:88–102Google Scholar
  13. Dixon JR, Presnall DC (1977) Geothermometry and geobarometry of synthetic spinel lherzolite in the system CaO-MgO-Al2O3-SiO2. Intern Kimberlite Conf 2, Ext Abstr: 85–87Google Scholar
  14. Eggler DH (1975) Peridotite-carbonate relations in the system CaO-MgO-SiO2-CO2. Carnegie Inst Wash Yearb 74:468–474Google Scholar
  15. Fujii T (1977) Pyroxene equilibria in spinel lherzolite. Carnegie Inst Wash Yearb 76:569–572Google Scholar
  16. Girardeau J (1982) Tectonic structures related to thrusting of ophiolitic complexes: the White-Hills peridotite, Newfoundland. Can J Earth Sc 19:709–722Google Scholar
  17. Girardeau J, Nicolas A (1981) The structures of two ophiolite massifs, Bay-of-Islands, Newfoundland: a model for the oceanic crust and upper mantle, Tectonophysics 77:1–34Google Scholar
  18. Girardeau J, Nicolas A, Marcoux J, Dupré B, Wang XB, Cao YG, Zheng HX, Xiao XC (1983a) Les ophiolites de Xigaze et la suture du Yarlung Zangbo, Tibet. Centre Nat Res Sc France Sp Pub: in pressGoogle Scholar
  19. Girardeau J, Mercier JCC, Cao YG (1983b) Structure of the Xigaze ophiolite, Yarlung Zangbo suture zone, Southern Tibet, China: genetic implications. Tectonics (in press)Google Scholar
  20. Holland TJB, Navrotsky A, Newton RC (1979) Thermodynamic parameters of CaMgSi2O6-Mg2Si2O6 pyroxenes based on regular solution and cooperative disordering models. Contrib Mineral Petrol 69:337–344Google Scholar
  21. Jenkins DM, Newton RC (1979) Experimental determination of the spinel peridotite to garnet peridotite inversion at 900° C and 1,000° C in the system CaO-MgO-Al2O3-SiO2, and at 900° C with natural garnet and olivine. Contrib Mineral Petrol 68:407–419Google Scholar
  22. Kushiro I (1969) The system forsterite-diopside-silica with and without water at high pressures. Am J Sci 267A:269–294Google Scholar
  23. Kushiro I (1972) Determination of liquidus relations in synthetic silicate systems with electron probe analysis: the system forsterite-diopside-silica at 1 atm. Am Mineral 57:1260–1271Google Scholar
  24. Kushiro I (1973) Partial melting of garnet lherzolites from kimberlite at high pressures. In “Lesotho kimberlites”, PH Nixon ed, LNDC, Maseru, Lesotho: 294–299Google Scholar
  25. Kushiro I, Yoder HS (1970) Stability field of iron-free pigeonite in the system MgSiO3 -CaMgSi2O6. Carnegie Inst Wash Yearb 68:226–229Google Scholar
  26. Kushiro I, Syono Y, Akimoto SI (1968 a) Melting of a peridotite nodule at high pressures and high water pressures. J Geophys Res 73:6023–6029Google Scholar
  27. Kushiro I, Yoder SH, Nishikawa M (1968b) Effect of water on the melting of enstatite. Bull Geol Soc Am 79:1685–1692Google Scholar
  28. Lane DL, Ganguly J (1980) Al2O3 solubility in orthopyroxene in the system MgO-Al2O3-SiO2: a reevaluation and mantle geotherms. J Geophys Res 85:6963–6972Google Scholar
  29. Lindsley DH, Dixon S (1976) Diopside-enstatite equilibria at 850° to 1,400° C, 5 to 35 kbar. Am J Sc 276:1285–1301Google Scholar
  30. Lindsley DH, Grover JE, Davidson PM (1981) The thermodynamics of the Mg2Si2O6-CaMgSi2O6 join: a review and a new model. Adv Phys Geochem 1:149–175Google Scholar
  31. Longhi J, Boudreau AE (1980) The orthoenstatite liquidus field in the system forsterite-diopsite-silica. Am Mineral 65:563–573Google Scholar
  32. Mercier JCC (1976) Single-pyroxene geothermometry and geobarometry. Am Mineral 61:603–615Google Scholar
  33. Mercier JCC (1977) Natural peridotites: chemical and rheological heterogeneity of the upper mantle. Ph D Thesis, SUNY, Stony Brook, NY 1–668Google Scholar
  34. Mercier JCC (1980 a) Single-pyroxene thermobarometry. Tectonophysics 70:1–37Google Scholar
  35. Mercier JCC (1980 b) Magnitude of the continental lithospheric stresses inferred from rheomorphic petrology. J Geophys Res 85:6293–6303Google Scholar
  36. Mercier JCC (1983) Thermobarometrie pyroxénique: quelques méthodes basées sur des réactions de transfert.In “Thermométrie et barométrie géologiques”, V. Gabis and M. Lagache eds, Soc Fr Minéral Cristal: in pressGoogle Scholar
  37. Mercier JCC, Carter NL (1975) Pyroxene geotherms. J Geophys Res 80:3349–3362Google Scholar
  38. Mori T, Green DH (1975) Pyroxenes in the system Mg2Si2O6-CaMgSi2O6 at high pressure. Earth Planet Sc Lett 26:277–286Google Scholar
  39. Mysen BO (1973) Melting of a hydrous mantle: phase relations of mantle peridotite with controlled water and oxygen fugacities. Carnegie Inst Wash Yearb 72:467–478Google Scholar
  40. Mysen BO, Kushiro I (1977) Compositional variations of coexisting phases with degree of melting of peridotite in the upper mantle, Am Mineral 62:843–865Google Scholar
  41. Nehru CE, Wyllie PJ (1974) Electron-microprobe measurement of pyroxenes coexisting with H2O-undersaturated liquid in the join CaMgSi2O6-Mg2Si2O6. Geochim Cosmochim Acta 43:55–60Google Scholar
  42. Nicolas A, Girardeau J, Marcoux J, Dupré B, Wang XB, Cao YG, Zheng HX, Xiao XC (1981) The Xigaze ophiolite, Tibet: a peculiar oceanic lithosphere. Nature 294:414–417Google Scholar
  43. Nixon PH, Boyd FR (1979) Garnet-bearing lherzolites and discrete nodule suites from the Malaita alnoite, Solomon Islands, SW Pacific and their bearing on oceanic mantle composition and geotherrn.In: The mantle sample: inclusions in kimberlites and other volcanics, FR Boyd and HOA Meyer eds, Am Geophys Union: 400–423Google Scholar
  44. Nixon PH, Coleman PJ (1978) Garnet-bearing lherzolites and discrete nodule suites from the Malaita alnoite, Solomon Islands, and their bearing on the nature and origin of the Ontong-Java Plateau. Bull Austr Soc Explor Geophys 9:103–107Google Scholar
  45. O'Hara MJ (1967) Mineral parageneses in ultrabasic rocks. In: Ultramafic and related rocks, PJ Wyllie ed, Wyley, New York: 393–403Google Scholar
  46. O'Hara MJ (1975) Pyroxene grids, paleogeotherms and a new mineral facies in the upper mantle. Int Conf Geothermometry Geobarometry Ext Abstr Penn State Univ, Pennsylvania: 123–126Google Scholar
  47. Oldenburg DW (1975) A physical model for the creation of the lithosphere. Geophys J 43:257–263Google Scholar
  48. Osawa K (1983) Evaluation of olivine spinel geothermometry as an indicator of thermal history for peridotites. Contrib Mineral Petrol 82:52–65Google Scholar
  49. Perkins DIII, Newton RC (1980) The composition of coexisting pyroxenes and garnet in the system CaO-MgO-Al2O-SiO2 at 900°-1,100° C and high pressures. Contrib Mineral Petrol 75:291–300Google Scholar
  50. Perkins DIII, Holland TJB, Newton RC (1981) The Al2O3 contents of enstatite in equilibrium with garnet in the system MgO -Al2O3 -SiO2 at 15–40 kbar and 900–1,600° C. Contrib Mineral Petrol 78:99–109Google Scholar
  51. Rabinowicz M, Nicolas A, Vigneresse JL (1984) A rolling-mill effect in asthenosphere beneath oceanic spreading centers. Earth Planet Sci Lett (in press)Google Scholar
  52. Saxena SK, Nehru CE (1975) Enstatite-diopside solvus and geothermometry. Contrib Mineral Petrol 49:259–267Google Scholar
  53. Streckeisen AL (1973) Plutonic rocks: classification and nomenclature recommended by the IUGS subcommission on the systematics of igneous rocks. Geotimes 18:26–30Google Scholar
  54. Warner RD (1975) New experimental data for the system CaO -MgO-SiO2-H2O and a synthesis of inferred phase relations. Geochom Cosmochom Acta 39:1413–1421Google Scholar
  55. Warner RD, Luth WC (1974) The diopside-orthoenstatite two-phase region in the system CaMgSi2O6-Mg2Si2O6. Am Mineral 59:98–109Google Scholar
  56. Wendlandt RF, Mysen BO (1978) Melting phase relations of natural peridotite+CO2 as a function of degree of partial melting at 15 and 30 kbar. Carnegie Inst Wash Yearb 77:756–761Google Scholar
  57. Wood BJ, Banno S (1973) Garnet-orthopyroxene and orthopyroxene-clinopyroxene relationships in simple and complex systems. Contrib Mineral Petrol 42:109–124Google Scholar
  58. Yamada H, Takahashi E (1983) Subsolidus phase relations between coexisting garnet and two pyroxenes at 50 to 100 kbar in the system CaO-MgO-Al2O3-SiO2. Dev Petrol 247–256Google Scholar
  59. Yang H, Foster WR (1972) Stability of iron-free pigeonite at atmospheric pressure. Am Mineral 57:1232–1241Google Scholar

Copyright information

© Springer-Verlag 1984

Authors and Affiliations

  • Jean -Claude C. Mercier
    • 1
  • Vincent Benoit
    • 1
  • Jacques Girardeau
    • 1
  1. 1.Institut de Physique du GlobeParis Cedex 05France

Personalised recommendations