Abstract
Manganese-rich metamorphic rocks containing violan from St. Marcel, Piedmont, Italy formed under blueschist facies conditions, yielding an unusual suite of minerals including omphacite-albite-quartz, braunite, microcline, hollandite, piedmontite, and strontian calcite. Violan, a violet-colored pyroxene, is shown to be a manganoan omphacite having a primitive unit cell, and is found in the same sample as diopside, possibly indicating a solvus relation. A manganoan phlogopite and a celadonitic muscovite coexist in one sample with microcline. The occurrence of celadonite and phlogopite is the first from the blueschist facies and the celadonite component in the dioctahedral mica is buffered at a maximum by coexistence with phlogopite, microcline, and quartz. Various phase relations are used to establish the P and T of equilibration at 8±1 kbar and 300±50 °C, respectively, while the oxygen fugacity is shown to have been very high, for these temperatures, as consistent with braunite+quartz and the presence of piedmontite.
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References
Barth, T.F.W.: The feldspar geologic thermometers. N.Jb. Mineral. Abh. 82, 143–154 (1951)
Bell, P.M., Davis, B.T.C.: Temperature-composition section for jadeite-diopside. Carnegie Inst. Wash. Year Book 64, 120–123 (1964)
Bell, P.M., Davis, B.T.C.: Investigation of a solvus in the system jadeite-diopside. Carnegie Inst. Wash. Year Book 65, 239–241 (1965)
Burnham, C.W.: Lattice constant refinement. Carnegie Inst. Wash. Year Book 61, 132–135 (1961)
Champness, P.E.: Speculation on an order-disorder transformation in omphacite. Am. Mineralogist 58, 540–542 (1973)
Clark, J.R., Papike, J.J.: Crystal-chemical characterization of omphacites. Am. Mineralogist 53, 840–868 (1968)
Coleman, R.G., Clark, J.R.: Pyroxenes in the blueschist facies of California. Am. J. Sci. 266, 43–59 (1968)
Dana, E.S.: Descriptive mineralogy. New York: John Wiley and Sons, Inc. 1892
Doelter, C.A.: Handbuch der Mineralchemie, Vol.2. Dresden und Leipzig: Verlag von Theodor Steonkopff 1912
Ernst, W.G.: Significance of phengitic micas from low-grade schists. Am. Mineralogist 48, 1357–1373 (1963)
Ernst, W.G.: Interpretative synthesis of metamorphism in the Alps. Bull. Geol. Soc. Am. 84, 2053–2078 (1973)
Essene, E.J.: Petrogenesis of Franciscan metamorphic rocks. Ph.D. Thesis, Univ. of California, Berkeley, CA (1967)
Essene, E.J.: Relatively pure Jadeite from a siliceous Corsican gneiss. Earth Planet. Sci. Lett. 5, 270–272 (1968)
Essene, E.J., Fyfe, W.S.: Omphacite in Californian metamorphic rocks. Contrib. Mineral. Petrol. 15, 1–23 (1967)
Essene, E.J., Ware, N.G.: The low temperature xenolithic origin of eclogites in diatremes, N.E. Arizona (abstr.). Geol. Soc. Am. Abstr. Progr. 2, 547–548 (1970)
Froese, E.: Calculated phase relations in the system CaCO3-SrCO3. Can. Mineralogist 10, 665–676 (1970)
Froese, E., Winkler, H.G.F.: The system CaCO3-SrCO3 at high pressures and 500 ° C to 700 ° C. Can Mineralogist 8, 551–566 (1966)
Fyfe, W.S., Verhoogen, J.: General thermodynamic considerations. In: Metamorphic reactions and metamorphic facies (W.S. Fyfe et al., eds.). Geol. Soc. Am. Mem. 73, 25–34 (1958)
Goldsmith, J.R., Newton, R.C.: An experimental determination of the alkali feldspar solvus. In: The feldspars (W.S. Mackenzie and J. Zussman, eds.), pp. 337–359. Manchester; England: Manchester University Press 1974
Hintze, C.: Handbuch der Mineralogie, Vol. 2. Leipzig: Verlag Von Vert and Comp. 1897
Huebner, J.: Stability relations of minerals in the system Mn-Si-C-O. Ph.D.Thesis. Baltimore, Maryland: Johns Hopkins University 1967
Huebner, J.: The manganese oxides-A bibliographic commentary. In: Oxide minerals (D. Rumble, ed.), pp. SH1–SH17. Mineral. Soc. Am. Short Course Notes 1977
Keskinen, M.J., Liou, J.G.: Synthesis and stability relations of Piedmontite, Ca2MnAl2Si3O12(OH) (abstr.). Geol. Soc. Am. Abstr. Progr. 8, 953–954 (1976)
Kushiro, I.: Clinopyroxene solid solutions at high pressures. Carnegie Inst. Wash. Year Book 64, 112–117 (1964)
Lorenzoni, S.: Studio geo-petrografico del versante Italiano del Massiccio D'Ambin. Memorie degl. Inst. Geol. Mineral. Univ. Padora 25, 88 p. (1965)
Luth, W.C., Fenn, P.M.: Peralkaline feldspar solvi. In: The feldspars (W.S. MacKenzie and J. Zussman, eds.), pp. 297–312. Manchester, England: Manchester University Press 1974
Muan, A.: Stability relations among some manganese minerals. Am. Mineralogist 44, 946–960 (1959)
Newton, R.C., Smith, J.V.: Investigations concerning the breakdown of albite at depth in the earth. J. Geol. 75, 268–286 (1967)
Phakey, P.P., Ghose, S.: Direct observation of anti-phase domain structure in omphacite. Contrib. Mineral. Petrol. 39, 239–245 (1973)
Plas, L. Van der: Petrology of the Northern Adula Region, Switzerland, (with particular reference to glaucophane-bearing rocks). Leidse Geol. Mededel. 24, 415–602 (1959)
Popp, R.K., Gilbert, M.C.: Stability of acmite-jadeite pyroxenes at low pressure. Am. Mineralogist 57, 1210–1231 (1972)
Prewitt, C.T., Burnham, C.W.: The crystal structure of jadeite; NaAlSi2O6. Am. Mineralogist 51, 956–975 (1966)
Robie, R.A., Waldbaum, D.R.: Thermodynamic properties of minerals and related substances at 298.15 ° K and one atmosphere pressure and at higher temperatures. U.S. Geol. Surv. Bull. 1259, 256 p. (1968)
Velde, B.: Phengitic micas: Synthesis, stability and natural occurrence. Am. J. Sci. 263, 886–913 (1965)
Whitney, J.A., Stormer, J.C.: The distribution of NaAlSi3O8 between coexisting microcline and plagioclase and its effect on geothermometric calculations. Am. Mineralogist 62, 687–691 (1977)
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Contribution No. 343, from the Mineralogical Laboratory, Department of Geology and Mineralogy, The University of Michigan, Ann Arbor, MI 48109, USA
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Brown, P., Essene, E.J. & Peacor, D.R. The mineralogy and petrology of manganese-rich rocks from St. Marcel, Piedmont, Italy. Contr. Mineral. and Petrol. 67, 227–232 (1978). https://doi.org/10.1007/BF00381450
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DOI: https://doi.org/10.1007/BF00381450