Abstract
Small volumes (in the cm3 range) of a talc-kyanite schist exhibit mosaic equilibria characterized by mineral assemblages conventionally attributed to vastly different pressure temperature conditions of metamorphism. On the basis of petrographic and microprobe studies these assemblages are attributed to three consecutive stages of metamorphism of a chemically exceptional rock composition falling largely into the model system MgO-Al2O3-SiO2-H2O. Stage 1 typified by Mg chlorite-quartz-talc and some paragonite was followed during stage 2 by talc-kyanite, Mg gedrite-quartz, and the growth of large dravites. In stage 3 pure Mg cordierite formed with or without corundum and/or talc, and kyanite was partly converted into sillimanite. Pressures and temperature during this final stage of metamorphism were probably near 5–6 kb, 640 ° C.
The preservation of this succession of mineral assemblages related to each other through isochemical reactions suggests that the main factors governing the metamorphic history of this whitheschist were compositional changes of the coexisting fluids with time, whereas pressure temperature variations may be subordinate. In the Sar e Sang area such chemical variations of the metamorphic fluids are probably caused by progressive metamorphism and mobilization of a former evaporite deposit.
Microprobe analyses of the phases gedrite and talc indicate variable degrees of sodium incorporation into these phases according to the substitution NaAl→Si.
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References
Becke, F.: Über Myrmekit. Tschermaks Mineral. Petrog. Mitt. 27, 377–390 (1908)
Carman, J.H.: Synthetic sodium phlogopite and its two hydrates: stabilities, properties, and mineralogic implications. Am. Mineralogist 59, 261–273 (1974)
Chatterjee, N.D.: Synthesis and upper stability of paragonite. Contrib. Mineral. Petrol. 27, 244–257 (1970)
Chatterjee, N.D.: The upper stability limit of the assemblage paragonite+quartz and its natural occurrences. Contrib. Mineral. Petrol. 34, 288–303 (1972)
Chatterjee, N.D.: Crystal-liquid-vapour equilibria involving paragonite in the system NaAlSi3O8-Al2O3-SiO2-H2O. Ing. J. Earth Sci. 1, 3–11 (1974)
Chatterjee, N.D., Froese, E.: A thermodynamic study of the pseudobinary join muscovite-paragonite in the system KAlSi3O8-NaAlSi3O8-Al2O3-SiO2-H2O. Am. Mineralogist 60, 985–993 (1975)
Chinner, G.A., Sweatman, T.R.: A former association of enstatite and kyanite. Mineral. Mag. 36, 1052–1060 (1968)
Deer, W.A., Howie, R.A., Zussman, J.: Rock-forming minerals, Vol. 3. London: Longmans 1962
Deer, W.A., Howie, R.A., Zussman, J.: Rock-forming minerals, Vol. 2. London: Longmans 1963
Evans, H.T., Appleman, D.E., Handwerker, D.S.: The least squares refinement of crystal unic cells with powder diffraction data by an automatic computer method (abstract). Am. Crystallogr. Assoc. Cambridge, Mass., Anuual Meeting Program, 42–43 (1963)
Fawcett, J.J., Yoder, H.S., Jr.: Phase relationship of chlorites in the system MgO-Al2O3-SiO2-H2O. Am. Mineralogist 51, 353–380 (1966)
Fornefeld, C.: Ein Beitrag zu den Phasenbeziehungen des Talk im System MgO-SiO2-H2O und die Gibbs'sche Bildungsenergie des Talk bei 298,15 ° K und 1 Bar. Dipl. Thesis, Ruhr-University Bochum 1975
Kleppa, O.J., Newton, R.C.: The role of solution calorimetry in the study of mineral equilibria. Fortschr. Mineral. 52, 3–20 (1975)
Kulke, H.G.: Metamorphism of evaporitic carbonate rocks (NW Africa and Afghanistan) and the formation of lapis lazuli. Abstr. 25. Intern. Geol. Congr. Sydney, Sect. 3B (1976)
Kulke, H.G., Schreyer, W.: Kyanite-talc schist from Sar e Sang, Afghanistan. Earth Planet. Sci. Lett. 18, 324–328 (1973)
McKie, D.: Yoderite, a new hydrous magnesium iron aluminosilicate from Mautia Hill, Tanganyika. Mineral. Mag. 32, 282–307 (1959)
Newton, R.C.: An experimental determination of the high-pressure stability limits of magnesian cordierite under wet and dry conditions. J. Geol. 80, 398–420 (1972)
Richardson, S.W., Gilbert, M.C., Bell, P.M.: Experimental determination of kyanite-andalusite and andalusite-sillimanite equilibria: the aluminium silicate triple point. Am. J. Sci. 267, 259–272 (1969)
Robinson, P., Ross, M., Jaffe, H.W.: Composition of the anthophyllite-gedrite series, comparisons of gedrite and hornblende, and the anthophyllite-gedrite solvus. Am. Mineralogist 56, 1005–1041 (1971)
Rosenberg, P.E., Foit, F.F., Jr.: Alkali-free tourmalines in the system MgO-Al2O3-SiO2-H2O-B2O3. GSA Annual Meetings Papers, Salt Lake City, 1250–1251 (1975)
Rossovskij, L.N.: Pegmatites in magnesite marbles near the precious spinel locality Kuli-Lal, South-west Pamirs (Russian). Mineraly SSSR 14, 166–181 (1963)
Schreyer, W.: Synthetische und natürliche Cordierite I. Mischkristallbildung synthetischer Cordierite und ihre Gleichgewichtsbeziehungen. Neues Jahrb. Mineral. Abhandl. 102, 39–67 (1964)
Schreyer, W.: Synthetische und natürliche Cordierite II. Die chemischen Zusammensetzungen natürlicher Cordierite und ihre Abhängigkeit von den PTX-Bedingungen bei der Gesteinsbildung. Neues Jahrb. Mineral. Abhandl. 103, 35–79 (1965)
Schreyer, W.: A reconnaissance study of the system MgO-Al2O3-SiO2-H2O at pressures between 10 and 25 kb. Carnegie Inst. Wash. Yearbook 66, 380–392 (1968)
Schreyer, W.: Whiteschist: a high-pressure rock and its geologic significance. J. Geol. 81, 735–739 (1973)
Schreyer, W.: Whiteschist, a new type of metamorphic rock formed at high pressures. Geol. Rundschau 63, 597–609 (1974)
Schreyer, W.: Whiteschists: Their compositions and pressure temperature regimes based on experimental, field, and petrographic evidence. Tectonophysics, in press (1977)
Schreyer, W., Abraham, K.: Peraluminous sapphirine as a metastable reaction product in kyanite-gedrite-talc schist from Sar e Sang, Afghanistan. Mineral. Mag. 40, 171–180 (1975)
Schreyer, W., Schairer, J.F.: Metastable solid solutions with quartz-type structures on the join SiO2-MgAl2O4. Z. Krist. 116, 60–82 (1961)
Schreyer, W., Schairer, J.F.: Metastable osumilite- and petalite-type phases in the system MgO-Al2O3-SiO2. Am. Mineralogist 47, 90–104 (1962)
Schreyer, W., Seifert, F.: Compatibility relations of the aluminium silicates in the systems MgO-Al2O3-SiO2-H2O and K2O-MgO-Al2O3-SiO2-H2O at high pressures. Am. J. Sci. 267, 371–388 (1969)
Schreyer, W., Yoder, H.S.: The system Mg-cordierite-H2O and related rocks. Neues Jahrb. Mineral. Abhandl. 101, 271–342 (1964)
Seifert, F.: Stability of the assemblage cordierite-corundum in the system MgO-Al2O3-SiO2-H2O. Contrib. Mineral. Petrol. 41, 171–178 (1973)
Seifert, F.: Boron-free kornerupine: a high-pressure phase. Am. J. Sci. 275, 57–87 (1975)
Seifert, F., Schreyer, W.: Lower temperature stability limit of Mg cordierite in the range 1–7 kb water pressure: a redetermination. Contrib. Mineral. Petrol. 27, 225–238 (1970)
Smith, J.V.: Critical review of synthesis and occurrence of plagioclase feldspars and a possible phase diagram. J. Geol. 80, 505–525 (1972)
Tröger, W.E.: Optische Bestimmung der gesteinsbildenden Minerale. Teil 2, 2. Aufl. 822 p. Stuttgart: E. Schweizerbart'sche Verlagsbuchhandlung 1969
Velde, B.: Phengite micas: Synthesis, stabilita and natural occurrence. Am. J. Sci. 236, 886–913 (1965)
Vrána, S., Barr, M.W.C.: Talc-kyanite-quartz schists and other high-pressure assemblages from Zambia. Mineral. Mag. 38, 837 (1972)
Yoder, H.S., Jr.: Aluminous anthophyllite: The MgO-Al2O3-SiO2-H2O system at 850 ° C and 10 kb. Carnegie Inst. Wash. Yearbook 70, 142–145 (1971)
Zotov, I.A., Sidorenko, G.A.: Magnesian gedrite from the southwestern Pamirs. Dokl. Akad. Nauk SSSR 180, 700–703 (1968)
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Schreyer, W., Abraham, K. Three-stage metamorphic history of a whiteschist from Sar e Sang, Afghanistan, as part of a former evaporite deposit. Contr. Mineral. and Petrol. 59, 111–130 (1976). https://doi.org/10.1007/BF00371302
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DOI: https://doi.org/10.1007/BF00371302