Contributions to Mineralogy and Petrology

, Volume 86, Issue 2, pp 107–118 | Cite as

Coesite and pure pyrope in high-grade blueschists of the Western Alps: a first record and some consequences

  • Christian Chopin


A pyrope-quartzite originally described by Vialon (1966) from the Dora Maira massif was resampled and reinvestigated. Garnet (up to 25 cm in size), phengite, kyanite, talc and rutile are in textural equilibrium in an undeformed matrix of polygonal quartz. The garnet is a pyrope-almandine solid solution with 90 to 98 mol % Mg end-member. It contains inclusions of coesite which has partially inverted to quartz, resulting in a typical radial cracking of the host garnet around the inclusions. Several lines of evidence show that coesite crystallised under nearly static pressure conditions and that the whole matrix has once been coesite.

The formidable pressures of formation implied (≧28 kbar) are independently indicated by i) the coexistence of nearly pure pyrope with free silica and talc, ii) the coexistence of jadeite with kyanite, iii) the high Si content of phengite. Water activity must have been low. The stability of talc-phengite and the presence of rare glaucophane inclusions in pyrope point to low formation temperatures (about 700 °C) and to a probable Alpine age for the assemblage.

This is evidence that low temperature gradients, how essentially transient they are, may nevertheless persist to considerable depths. Moreover, the upper crustal (evaporite-related?) origin of the quartzite and its interbedding within a continental unit implies that continental crust may also be subducted to depths of 90 km or more. The return back to the surface is problematic; the retrograde assemblages observed show that it must be tectonic. If the rocks remain at depth, new perspectives open for the genesis of intermediate to acidic magmas. Eventually, the role of continental crust in geodynamics may have to be reconsidered.


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  1. Abraham K, Schreyer W (1975) A talc-phengite assemblage in piemontite schist from Brezovica, Serbia, Yugoslavia. J Petrol 17:421–439Google Scholar
  2. Ackermann L, Cemič L, Langer K (1983) Hydrogarnet substitution in pyrope: a possible location for “water” in the mantle. Earth Planet Sci Lett 62:208–214Google Scholar
  3. Bearth P (1952) Geologie und Petrographie des Monte Rosa. Beitr Geol Karte Schweiz NF 132: p 130Google Scholar
  4. Boyd FR, England JL (1959) Pyrope. Carnegie Inst Washington Yearb 58:83–87Google Scholar
  5. Boyd RF, England JL (1960) The quartz-coesite transition. J Geophys Res 65:749–756Google Scholar
  6. Carpenter MA (1980) Mechanisms of exsolution in sodic pyroxenes. Contrib Mineral Petrol 71:289–300Google Scholar
  7. Chao ETC, Shoemaker EM, Madsen BM (1960) First natural occurrence of coesite. Science 132:220–222Google Scholar
  8. Chesnokov BV, Popov VA (1965) Increase in the volume of quartz grains in South Urals eclogite. Dokl Akad Nauk SSSR 162:176–178Google Scholar
  9. Chinner GA, Dixon J (1973) Some high-pressure parageneses of the Allalin gabbro, Valais, Switzerland. J Petrol 14:185–202Google Scholar
  10. Chopin C (1979) De la Vanoise au massif du Grand Paradis. Thèse 3ème cycle Univ P et M Curie Paris:p 145Google Scholar
  11. Chopin C (1981) Talc-phengite: a widespread assemblage in highgrade pelitic blueschists of the Western Alps. J Petrol 22:628–650Google Scholar
  12. Chopin C (1983) High-pressure facies series in pelitic rocks: a review. Terra Cognita 3:183 (abstr)Google Scholar
  13. Chopin C, Maluski H (1980) 40Ar-39Ar dating of high-pressure metamorphic micas from the Gran Paradiso area (Western Alps): evidence against the blocking temperature concept. Contrib Mineral Petrol 74:109–122Google Scholar
  14. Chopin C, Monié P (1984) A unique Mg-chloritoid-bearing, highpressure assemblage from the Monte Rosa, Western Alps: a petrologic and 40Ar-39Ar radiometric study. (Submitted to Contrib Mineral Petrol)Google Scholar
  15. Chopin C, Schreyer W (1983) Magnesiocarpholite and magnesiochloritoid: two index minerals of pelitic blueschists and their preliminary phase relations in the model system MgO-Al2O3-SiO2-H2O. Am J Sci Orville vol:72–96Google Scholar
  16. Coes L (1953) A new dense crystalline silica. Science 118:131–152Google Scholar
  17. Compagnoni R (1977) The Sesia-Lanzo zone: high-pressure, lowtemperature metamorphism in the Austroalpine continental margin. Rend Soc Ital Mineral Petrol 33:325–374Google Scholar
  18. Desmons J, O'Neil JR (1978) Oxygen and hydrogen isotope compositions of eclogites and associated rocks from the eastern Sesia zone (Western Alps, Italy). Contrib Mineral Petrol 67:79–85Google Scholar
  19. Franchi S (1900) Sopra alcuni giacimenti di roccie giadeitiche nelle Alpi occidentali e nell'Appennino ligure. Boll R Comit Geol Ital (IV) 1:119–158Google Scholar
  20. Ganguly J (1969) Chloritoid stability and related parageneses: theory, experiments and applications. Am J Sci 267:910–944Google Scholar
  21. Gillet P, Ingrin J, Chopin C (1984) Coesite in subducted continental crust: (P, T) history deduced from an elastic model. (Submitted to Earth Planet Sci Lett)Google Scholar
  22. Goffé B (1982) Définition du faciès à Fe-Mg-carpholite-chloritoïde, marqueur du métamorphisme de haute pression-basse température. Thèse d'état Univ P et M Curie ParisGoogle Scholar
  23. Goffé B, Velde B (1984) Contrasted metamorphic evolutions in thrusted cover units of the Briançonnais zone (French Alps): a model for the conservation of HP-LT metamorphic mineral assemblages. Earth Planet Sci Lett (in press)Google Scholar
  24. Green HW (1974) Metastable growth of coesite in highly strained quartz. J Geophys Res 77:2478–2482Google Scholar
  25. Halbach H, Chatterjee ND (1982) An empirical Redlich-Kwong type equation of state for water to 1000° C and 200 kbar. Contrib Mineral Petrol 79:337–345Google Scholar
  26. Hamilton W (1979) Tectonics of the Indonesian region. US Geol Survey Prof Paper 1078Google Scholar
  27. Hensen BJ, Essene EJ (1971) Stability of pyrope-quartz in the system MgO-Al2O3-SiO2. Contrib Mineral Petrol 30:72–83Google Scholar
  28. Hobbs BE (1968) Recrystallization of single crystals of quartz. Tectonophysics 6:353–401Google Scholar
  29. Holland TJB (1979a) High water activities in the generation of high-pressure kyanite eclogites of the Tauern Window, Austria. J Geol 87:1–27Google Scholar
  30. Holland TJB (1979b) Experimental determination of the reaction paragonite=jadeite+kyanite+water, and internally consistent thermodynamic data for part of the system Na2O-Al2O3-SiO2-H2O, with applications to eclogites and blueschists. Contrib Mineral Petrol 68:293–301Google Scholar
  31. Holland TJB (1980) The reaction albite=jadeite+quartz determined experimentally in the range 600–1200° C. Am Mineral 65:129–134Google Scholar
  32. Kitahara S, Takenouchi S, Kennedy GC (1966) Phase relations in the system MgO-SiO2-H2O at high temperatures and pressures. Am J Sci 264:223–233Google Scholar
  33. Lazko YY, Koptil VI, Serenko VP, Tsepin AI (1983) Fassaite clinopyroxenes from diamond-bearing kyanite eclogite xenoliths. Dokl Earth Sci Section 258:138–142Google Scholar
  34. MacDonald GJF (1956) Quartz-coesite stability relations at high temperatures and pressures. Am J Sci 254:713–721Google Scholar
  35. Massonne HJ (1981) Phengite: eine experimentelle Untersuchung ihres Druck-Temperatur-Verhaltens im System K2O-MgO-Al2O3-SiO2-H2O. Dissertation Ruhr-Universität BochumGoogle Scholar
  36. Massonne HJ (1983) Experiments on melting to 50 kbar in the system MgO-Al2O3-SiO2-H2O (MASH) with excess SiO2 and H2O (abstract). EOS Trans AGU 64:875Google Scholar
  37. Massonne HJ, Mirwald PW, Schreyer W (1981) Experimentelle Überprüfung der Reaktionskurve Chlorit+Quarz=Talk+Disthen im System MgO-Al2O3-SiO2-H2O. Fortschr Mineral 59:122–123Google Scholar
  38. Meyer HOA, Boyd FR (1972) Composition and origin of crystalline inclusions in diamonds. Geochim Cosmochim Acta 36:1255–1273CrossRefGoogle Scholar
  39. Miller C (1977) Chemismus und phasenpetrologische Untersuchung der Gesteine aus der Eklogitzone des Tauernfensters, Österreich. Tschermaks Mineral Petrogr Mitt 24:221–277Google Scholar
  40. Mirwald PW, Massonne HJ (1980) The low-high quartz and quartz-coesite transition to 40 kbar between 600° C and 1600° C and some reconnaissance data on the effect of NaAlO2 component on the low quartz-coesite transition. J Geophys Res 85:6983–6990Google Scholar
  41. Naka S, Ito S, Inagaki M (1972) Effect of shear on the quartz-coesite transition. J Am Ceramic Soc 55:323–324Google Scholar
  42. Newton RC (1972) An experimental determination of the high-pressure stability limits of magnesian cordierite under wet and dry conditions. J Geol 80:398–420Google Scholar
  43. Råheim A, Green DH (1974) Talc-garnet-kyanite-quartz schist from an eclogite-bearing terrane, Western Tasmania. Contrib Mineral Petrol 43:223–231Google Scholar
  44. Rao BB, Johannes W (1979) Further data on the stability of staurolite+quartz and related assemblages. Neues Jahrb Mineral Monatsh 10:437–447Google Scholar
  45. Rosenfeld JL, Chase AB (1961) Pressure and temperature of crystallisation from elastic effects around solid inclusions in minerals. Am J Sci 259:519–541Google Scholar
  46. Schreyer W (1968) A reconnaissance study of the system MgO-Al2O3-SiO2-H2O at pressures between 10 and 25 kbar. Carnegie Inst Wash Yearb 66:380–392Google Scholar
  47. Schreyer W (1977) Whiteschists: their compositions and pressure-temperature regimes based on experimental, field, and petrographic evidence. Tectonophysics 43:127–144Google Scholar
  48. Schreyer W, Abraham K (1976) Three stage metamorphic history of a whiteschist from Sar e Sang, Afganistan, as part of a former evaporite deposit. Contrib Mineral Petrol 59:111–130Google Scholar
  49. Schreyer W, Abraham K, Kulke H (1980) Natural sodium phlogopite coexisting with potassium phlogopite and sodian aluminian talc in a metamorphic evaporite sequence from Derrag, Tell Atlas, Algeria. Contrib Mineral Petrol 74:223–233Google Scholar
  50. Schreyer W, Baller T (1977) Talc-muscovite: synthesis of a new high-pressure phyllosilicate assemblage. Neues Jahrb Mineral Monatsh 9:421–425Google Scholar
  51. Silver EA, Reed D, McCaffrey R (1983) Back arc thrusting in the Eastern Sunda arc, Indonesia: a consequence of arc-continent collision. J Geophys Res 88:7429–7448Google Scholar
  52. Smyth JR (1977) Quartz pseudomorphs after coesite. Am Mineral 62:828–830Google Scholar
  53. Smyth JR, Hatton CJ (1977) A coesite-sanidine grospydite from the Roberts Victor kimberlite. Earth Planet Sci Lett 34:284–290Google Scholar
  54. Sobolev NV et al. (1976) Coesite, garnet and omphacite inclusions in Yakut diamonds — first finding of coesite paragenesis. Dokl Akad Nauk SSSR 230:1442–1444 (in Russian) Abstr in Mineral Abstr 78–818Google Scholar
  55. Stella A (1895) Sul rilevamento geologico eseguito nel 1894 in Valle Varaita (Alpi Cozie). Boll R Comit Geol Ital 26:283–313Google Scholar
  56. Udovkina NG, Muravitskaya GN, Laputina IP (1978) Phase equilibria in the talc-garnet-kyanite rocks of the Kokchetav block, Northern Kazakhstan. Isvestiya Akad Nauk SSSR Geol section 7:55–64 (in Russian)Google Scholar
  57. Udovkina NG, Muravitskaya GN, Laputina IP (1980) Talc-garnet-kyanite rocks of the Kokchetav block, Northern Kazakhstan. Dokl Earth Sci section 237:202–205Google Scholar
  58. Velde B (1967) Si content of natural phengites. Contrib Mineral Petrol 14:250–258Google Scholar
  59. Vialon P (1966) Etude géologique du massif cristallin Dora-Maira, Alpes cottiennes internes, Italie. Thèse d'état Univ GrenobleGoogle Scholar

Copyright information

© Springer-Verlag 1984

Authors and Affiliations

  • Christian Chopin
    • 1
  1. 1.ER 224, Laboratoire de GéologieEcole Normale SupérieureParisFrance

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