Summary
The Middle Proterozoic Faraday Metagabbro in the Bancroft area of eastern Ontario has been subjected to syn-orogenic textural and mineralogical modifications resulting in the formation of scapolite-bearing metagabbro and gabbroic blastomylonite assemblages. The elemental flux during cryptic and overt scapolitization has been calculated usingGresens general metasomatic equation which applies corrections for density and volume changes during alteration. Metasomatic variation diagrams using analyses from two primary gabbros and six altered rocks indicate that Na, K, Cl, Li, Rb, and Ba are the principal introduced elements and that Cu and S were removed. These changes are very similar to those involved in the formation of metasomatic nepheline-bearing rocks elsewhere in the district and, furthermore, nephelinization and scapolitization were broadly coincident in time and space. It is concluded that the nephelin- and scapolite-bearing rocks and their cryptic facies are different manifestations of the same metasomatic agent and that the source of the fluids was a possible horizon of evaporitic sediments within the country rocks in which the gabbro was emplaced.
Zusammenfassung
Der Mittel-proterozoische Faraday-Gabbro in der Umgebung von Bancroft (Ost-Ontario) erfuhr synorogene Veränderungen in Textur und Mineralogie, die zur Bildung skapolit-haltiger Metagabbros und gabbroider Blastomylonite führten. Die während kryptischer und offener Skapolitisierung stattfindende Elementtransport wurde mit Hilfe der vonGresens entwickelten generellen metasomatischen Gleichung errechnet; Korrekturen für Varänderungen in spezifischer Dichte und Volumen wurden angebracht. Metasomatische Variationsdiagramme basierend auf Analysen an zwei primären Gabbros und sechs modifizierten Gesteinen zeigen, daß Na, K, Cl, Li, Rb und Ba die hauptsächlich zugeführten Elemente darstellen, und daß Cu-und S-Konzentrationen abgebaut wurden. Diese Veränderungen sind vergleichbar mit solchen, wie sie bei der Bildung metasomatischer, Nephelin-haltiger Gesteine erkannt wurden. Außerdem fallen Nephelinisierung und Skapolitisierung zeitlich und räumlich in etwa zusammen. Daraus kann geschlossen werden, daß Nephelin- und Skapolit-haltige Gesteine und deren kryptische Phasen durch den gleichen metasomatischen Prozeß entstanden sind, und daß die Herkunft der umwandelnden Lösungen möglicherweise in evaporitischen Sedimenten zu suchen ist, in die der Gabbro intrudierte.
Similar content being viewed by others
References
Abbey, S., 1977: Studies in “Standard Samples” for use in the general analysis of silicate rocks and minerals. Geol. Surv. Canada, Paper 77-34.
Adams, F. D., Barlow, A. E., 1908: The nepheline and associated alkali-syenites of eastern Ontario. Trans. Roy. Soc. Canad2, sec. iv, 3–76.
Appleyard, E. C., 1963: Nepheline gneisses of the Wolfe Belt, Lyndoch Township, Ontario. Unpublished Ph.D. thesis, Cambridge University, England.
— 1965: The Grenville Province and its tectonic significance — a discussion. Proc. Geol. Assoc. Canada16, 51–57.
— 1967: Nepheline gneisses of the Wolfe Belt, Lyndoch Township, Ontario. I. Structure, stratigraphy, and petrography. Can. J. Earth Sci.4, 371–395.
— 1969: Nepheline gneisses of the Wolfe Belt, Lyndoch Township, Ontario. II. Textures and mineral paragenesis. Can. J. Earth Sci.6, 689–717.
— 1974a: Basement/cover relationships within the Grenville province in eastern Ontario. Can. J. Earth Sci.11, 369–379.
— 1974b: Syn-orogenic igneous alkaline rocks of eastern Ontario and northern Norway. Lithos7, 147–169.
— 1980: Mass balance computations in metasomatism: metagabbro/nepheline syenite pegmatite interaction in northern Norway. Contr. Min. Petr.73, 131–144.
Appleyard, E. C. Stott, G. M., 1975: Grenville gneisses in the Madawaska highlands, eastern Ontario. Geol. Assoc. Canada, Min. Assoc. Canada, Geol. Soc. Amer. Field Trips Guidebook, Part A, 26–62, i–xxix.
—, 1979: Fenitization: an example of the problems of characterizing mass transfer and volume changes. Chem. Geol.26, 1–15.
Babcock, R. S., 1973: Computational models of metasomatic processes. Lithos6, 279–290.
Best, M. G., 1966: Structural geology of Precambrian rocks south of Bancroft, Ontario. Can. J. Earth Sci.3, 441–455.
Currie, K. L., 1976: The alkaline rocks of Canada. Geol. Surv. Canada, Bull. 239.
Divi, R. R., 1972: Structural analysis of Grenville rocks near Bancroft, Ontario, Canada. Unpublished Ph.D. thesis, University of Ottawa, Canada.
—, 1973: Folds and strain in Grenville metamorphic rocks, Bancroft, Ontario, Canada. Bull. Geol. Soc. Am.84, 1607–1618.
Gittins, J., 1961: Nephelinization in the Haliburton-Bancroft district, Ontario, Canada. J. Geol.69, 291–308.
Gresens, R. L., 1967: Composition-volume relationships of metasomatism. Chem. Geol.2, 47–65.
Gummer, W. K., Burr, S. V., 1946: Nephelinized paragneisses in the Bancroft area. J. Geol.54, 137–168.
Hewitt, D. F., 1959: Geology of Cardiff and Faraday Townships. Ont. Dept. Mines Ann. Rept.66, part 3, for 1957.
Jennings, D. S., 1969: Origin and metamorphism of part of the Hermon Group near Bancroft, Ontario. Unpublished Ph.D. thesis, McMaster University, Canada.
Karvinen, W. O., 1973: Metamorphogenic molybdenite deposits in the Grenville province. Unpublished Ph.D. thesis, Queen's University (Kingston), Canada.
Little, H. W., 1969: Anhydrite — pegmatite uranium ore at Bancroft, Ontario. Econ. Geol.64, 691–695.
Maxwell, J. A., 1968: Rock and Mineral Analysis. New York: Interscience (Chemical Analysis,27).
Mitchell, S. L., 1976: Structure and petrology of the Bentley-Siddon Lakes area, Bancroft, Ontario with special reference to rocks of alkaline affinity. Unpublished M.Sc. thesis, University of Waterloo, Canada.
Osborne, F. F., 1930: The nepheline gneiss complex near Egan Chute, Dungannon Township, and its bearing on the origin of the nepheline syenite. Am. J. Sci.20, ser. v, 33–60.
Serdyuchenko, D. P., 1975: Some Precambrian scapolite-bearing rocks evolved from evaporites. Lithos8, 1–7.
Sharpiro, L., Brannock, W. W., 1955: Rapid determination of water in silicate rocks. Anal. Chem.27, 560–562.
Tilley, C. E., Gittins, J., 1961: Igneous nepheline-bearing rocks of the Haliburton-Bancroft province of Ontario. J. Petrol.2, 38–50.
Author information
Authors and Affiliations
Additional information
With 3 Figures
Rights and permissions
About this article
Cite this article
Appleyard, E.C., Williams, S.E. Metasomatic effects in the Faraday Metagabbro, Bancroft, Ontario, Canada. TMPM Tschermaks Petr. Mitt. 28, 81–97 (1981). https://doi.org/10.1007/BF01081547
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF01081547