Abstract
High-pressure metamorphism (∼600° C, ∼20 kbar) of the Allalin Gabbro (Western Alps) resulted in the breakdown of plagioclase (∼An63) to fine-grained zoisite, jadeite, kyanite and quartz. In rare cases this reaction failed to reach completion. The resulting textures of partial reaction have been studied by transmission and analytical electron microscopy. In localised regions of a plagioclase crystal where the extent of reaction is <10%, only zoisite developed and the orientation relationship
and
is frequently present. In regions where 10–50% of plagioclase has transformed, the reaction plagioclase+H2O→zoisite+kyanite+quartz +(NaSiCa−1Al−1)pl has occurred. The systematic orientation relationship between plagioclase and zoisite is absent at ≥50% transformation. Complete breakdown of plagioclase occurred in localized micron-scale domains by the reaction plagioclase+H2O→zoisite+jadeite+kyanite+quartz and the reaction products are variably orientated with respect to each other. Incomplete reaction, together with the concentration of reaction products around cracks in original plagioclase grains, suggests that extent of reaction was controlled primarily by the availability of H2O. The textural observations are interpreted in terms of two possible disequilibrium reaction models. (1) Plagioclase persists metastably with its original igneous composition to a pressure > 17 kbar at 600° C. Reaction to the equilibrium assemblage then develops adjacent to cracks in response to the presence of aqueous fluid. At intracrystalline sites, only partial reaction occurs because Jadeite, and sometimes kyanite and quartz, fail to nucleate for kinetic reasons. (2) Localized regions of a plagioclase crystal partially equilibrate at several stages during the increase of pressure (∼9–17 kbar at 600° C), possibly due to discrete episodes of fluid infiltration. In both these models, the extent of reaction may be limited by NaSi-CaAl interdiffusion in plagioclase.
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References
Barnicoat AC, Fry N (1986) High-pressure metamorphism in the Zermatt-Saas ophiolite zone, Switzerland. J Geol Soc London 143:607–618
Bearth P (1967) Die Ophiolithe der Zone von Zermatt-Saas Fee. Beitr Geol Karte Schweiz NF 132
Bocquet J, Delaloye M, Hunziker JC, Krummenacher D (1974) K-Ar and Rb-Sr dating of blue amphiboles, micas and associated minerals from the Western Alps. Contrib Mineral Petrol 47:7–26
Carpenter MA, Ferry JM (1984) Constraints on the thermodynamic mixing properties of plagioclase feldspars. Contrib Mineral Petrol 87:138–148
Carpenter MA, McConnell JDC (1984) Experimental determination of the C¯1⇄I¯1 transformation in intermediate plagioclase feldspars. Am Mineral 69:112–121
Champness PE, Cliff G, Lorimer GW (1982) Quantitative analytical electron microscopy of metals and minerals. Ultramicroscopy 8:121–132
Chinner GA, Dixon JE (1973) Some high-pressure parageneses of the Allalin gabbro, Valais, Switzerland. J Petrol 14:185–202
Chopin C (1981) Talc-phengite: a widespread assemblage in high- grade pelitic blueschists of the Western Alps. J Petrol 22:628–650
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 74:109–122
Compagnoni R, Dal Piaz GV, Hunziker JC, Gosso G, Lombardo B, Williams PF (1977) The Sesia-Lanzo Zone, a slice of continental crust with alpine high pressure-low temperature assemblages in the Western Italian Alps. Rend Soc Ital Mineral Petrol 33:281–334
Cliff G, Lorimer GW (1975) Quantitative analysis of thin specimens. J Microsc 103:203–207
Delaloye M, Desmons J (1976) K-Ar radiometric age determinations of white micas from the Piemont zone, French-Italian Western Alps. Contrib Mineral Petrol 57:293–303
Ernst WG, Dal Piaz GV (1978) Mineral parageneses of eclogites and related schists of the piemonte ophiolite Nappe, Breuil-St. Jaques area, Italian Western Alps. Am Mineral 63:621–640
Goldsmith JR (1982) Plagioclase stability at elevated temperatures and water pressures. Am Mineral 67:653–675
Grove TL, Baker MB, Kinzler RJ (1984) Coupled CaAl-NaSi diffusion in plagioclase feldspar: experiments and applications to cooling rate speedometry. Geochim Cosmochim Acta 48:2113–2121
Holland TJB, Powell R (1985) An internally consistent thermodynamic dataset with uncertainties and correlations. 2: Data and results. J Metamorphic Geol 3:343–370
Hunziker JC (1974) Rb-Sr and K-Ar age determinations and the Alpine tectonic history of the Western Alps. Mem Inst Geol Min Univ Padova 31:55 pp
Koons PO, Rubie DC, Frueh-Green G (1987) The effects of disequilibrium and deformation on the mineralogical evolution of quartz diorite during metamorphism in the eclogite facies. J Petrol 28:679–700
McGill JR, Hubbard FH (1981) Thin film K-value calibration for low atomic number elements using silicate mineral standards In: Lorimer GW, Jacob MN, Doig P (eds) Quantitative microanalysis with high spatial resolution. The Metals Society, London, pp 30–34
Meyer J (1983a) Mineralogie und Petrologie des Allalingabbros. PhD Thesis University of Basel, pp 331
Meyer J (1983b) The development of the high pressure metamorphism in the Allalin metagabbro (Switzerland). Terra Cognita 3:187 (abstr)
Mørk MBE (1985a) A gabbro to eclogite transformation on Flemsøy, Sunnmøre, western Norway. Chem Geol 50:283–310
Mørk MBE (1985b) Incomplete high P-T metamorphic transformations within the Kvamsøy pyroxenite complex, west Norway: a case study of disequilibrium: J Metamorphic Geol 3:245–264
Newton RC, Kennedy GC (1963) Some equilibrium relations on the join CaAl2Si2O8-H2O. J Geophys Res 68:2967–2983
Newton RC, Charlu TV, Kleppa OJ (1980) Thermochemistry of high structural state plagioclases. Geochim Cosmochim Acta 44:933–941
Otten MT, Buseck PR (1987) TEM study of the transformation of augite to sodic pyroxene in eclogitized ferrogabbro. Contrib Mineral Petrol 96:529–538
Pognante U (1985) Coronitic reactions and ductile shear zones in eclogitised ophiolite metagabbro, Western Alps, North Italy. Chem Geol 50:99–109
Pognante U, Kienast JR (1987) Blueschist and eclogite transformations in Fe-Ti gabbros: A case study from the Western Alps Ophiolites. J Petrol 28:271–292
Ridley J, Dixon JE (1984) Reaction pathways during the progressive deformation of a deformed blueschist metabasite: the role of chemical disequilibrium and restricted range equilibrium. J Metamorphic Geol 2:115–128
Rubie DC (1986) The catalysis of mineral reactions by water and restrictions on the presence of aqueous fluid during metamorphism. Mineral Mag 50:399–415
Smith JV, Brown WL (1988) Feldspar minerals. 1: Crystal structures, physical, chemical and microtextural properties, 2nd edn. Springer, Berlin Heidelberg New York Tokyo, pp 828
Wirth R (1986) Thermal alteration of glaucophane in the contact aureole of the Traversella Intrusion (N. Italy). Neues Jahrb Mineral Abh 152:193–205
Yardley BWD, Baltatzis E (1985) Retrogression of staurolite schists and the sources of infiltrating fluids during metamorphism. Contrib Mineral Petrol 89:59–68
Yund RA (1986) Interdiffusion of NaSi-CaAl in peristerite. Phys Chem Mineral 13:11–16
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Wayte, G.J., Worden, R.H., Rubie, D.C. et al. A TEM study of disequilibrium plagioclase breakdown at high pressure: the role of infiltrating fluid. Contr. Mineral. and Petrol. 101, 426–437 (1989). https://doi.org/10.1007/BF00372216
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DOI: https://doi.org/10.1007/BF00372216