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Contrasting garnet parageneses in a composite Grenvillian granitoid pluton, Newfoundland

Published online by Cambridge University Press:  05 July 2018

J. Victor Owen  and
Robert A. Marr
J. Victor Owen
Affiliation:
Department of Geology, Saint Mary's University, Halifax, Nova Scotia, Canada B3H 3C3
Robert A. Marr
Affiliation:
Department of Geology, Saint Mary's University, Halifax, Nova Scotia, Canada B3H 3C3
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Abstract

Almandine- and grossular-rich garnet occurs as both a coronitic and non-coronitic phase in ferruginous, Grenvillian (c. 1050 Ma) granitoid rocks of the composite Potato Hill pluton of the Long Range Inlier, Newfoundland. The country rock includes garnetiferous gneiss, but garnets in the pluton are compositionally distinct (higher Ca and Mn, lower Mg), so none are interpreted as xenocrysts from the Long Range gneiss complex.

Coronal garnet, quartz and hornblende separate primary pyroxene, ilmenite and hornblende from feldspar in two-pyroxene charnockite. Balanced mass-transfer reactions based on microprobe data and modes for the pyroxene-centred corona structures suggest that corona sites gained Fe and lost Na. The flux of Fe apparently controlled corona growth in the charnockite. The corona structures are attributed to subsolidus cooling of the pluton rather than to a metamorphic overprint because the coronas are obliterated in high strain zones cutting the charnockite. Temperature of formation is constrained at c. 775–630°C by two-pyroxene and garnet-hornblende thermometry. Compositionally-similar coronas in rare, Fe-rich enderbite of the Long Range gneiss complex probably formed during cooling after early, high-grade metamorphism or following the regional emplacement of the Grenvillian plutons.

Non-coronitic garnets occur in equigranular and megacrystic hornblende-biotite granite. Garnets in the equigranular granite are large, well-formed, and in some instances are associated with compositional layering of probable igneous origin. These garnets are enriched in grossular (XCa = 0.28), and are therefore interpreted as phenocrysts crystallized at high pressure (>9 kbar?). They would nevertheless have been stabilized to lower pressures by their moderate spessartine content (XMn = 0.13).

Garnets in foliated megacrystic granite form tiny crystals depleted in Fe and Mg, and enriched in Mn and Ca, and in these respects are similar to garnet in deformed charnockite. These garnets are therefore interpreted to have formed (or re-equilibrated) during the late Grenvillian deformation. Garnet is absent in relatively magnesian Grenvillian granites (bulk XFe2+ = 0.50–0.85) elsewhere in the inlier. The restriction of garnet to the Potato Hill pluton (bulk XFe2+ = 0.88–0.94) therefore testifies to bulk compositional controls on the formation of both magmatic and subsolidus garnet in this intrusion.

Keywords

garnetcorona structureGrenvillian granitesNewfoundlandCanada
Type
Silicate Mineralogy
Information
Mineralogical Magazine , Volume 54 , Issue 376 , September 1990 , pp. 367 - 380
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1990

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Footnotes

*

Present address: Department of Geological Sciences, McGill University, Montreal, Quebec, Canada H3A 2A7

References

Allan, B. D. and Clarke, D. B. (1981) Occurrence and origin of garnets in the South Mountain batholith, Nova Scotia. Can. Mineral. 19, 19-24.Google Scholar
Ashworth, J. R. (1986) The role of magmatic reaction, diffusion, and annealing in the evolution of coronitic microstructure in troctolitic gabbro from Risor, Norway: a discussion. Mineral. Mag. 50, 469-73.CrossRefGoogle Scholar
Baadsgaard, H., Erdmer, P. and Owen, J. V. (in prep.) U-Pb geochronology of the Long Range Inlier, New-foundland. (submitted to Geol. Soc. Amer. Bull.)Google Scholar
Bhattacharyya, P. K. and Mukherjee, S. (1987) Granulites in and around the Bengal anorthosite, eastern India: genesis of coronal garnet, and evolution of the granulite-anorthosite complex. Geol. Mag. 124, 21-32.CrossRefGoogle Scholar
Brady, J. B. (1975) Reference frames and diffusion coefficients. Amer. J. Sci. 275, 954-83.CrossRefGoogle Scholar
Cawthorn, R. G. and Brown, P. A. (1976) A model for the formation and crystallization of corundum-normative calc-alkaline magmas through amphibole fractionation. J. Geol. 84, 467-76.CrossRefGoogle Scholar
Cawthorn, R. G. and Brown, P. A. (1978) A model for the formation and crystallization of corundum-normative calc-alkaline magmas through amphibole fraction: a reply. Ibid. 86, 272-5.Google Scholar
Chamberlain, C. P. and Lyons, J. B. (1983) Pressure, temperature and metamorphic zonation studies of pelitic schists in the Merrimack Synclinorium, southcentral New Hampshire. Amer. Mineral. 68, 530-40.Google Scholar
Davidson, A. and van Breeman, O. (1988) Baddeleyite–zircon relationships in coronitic metagabbro, Grenville Province, Ontario: implications for geochronology. Contrib. Mineral. Petrol. 100, 291-9.CrossRefGoogle Scholar
Fitton, J. G. (1972) The genetic significance of almandine-pyrope phenocrysts in the calc-alkaline Borrowdale Volcanic Group, northern England. Ibid. 36, 231-48.CrossRefGoogle Scholar
Graham, C. M. and Powell, R. (1984) A garnet-hornblende geothermometer: calibration, testing, and application to the Pelona Schist, southern California. J. Metamorphic Geol. 2, 13-31.CrossRefGoogle Scholar
Green, T. H. (1977) Garnet in silicic liquids and its possible use as a P-T indicator. Contrib. Mineral. Petrol. 65, 59-67.CrossRefGoogle Scholar
Green, T. H. and Ringwood, A. E. (1968) Origin of garnet phenocrysts in calc-alkaline rocks. Ibid. 18, 163-74.CrossRefGoogle Scholar
Harem, H. M. and Vieten, K. (1971) Zur Berechnung der Kristallchemischen Formel und des Fe3+- Gehaltes von Klinopyroxenen aus Elektronen-strahl- Microanalysen. Neues Jahrb. Mineral. Mh., 310-5.Google Scholar
Harrison, T. N. (1988) Magmatic garnets in the Cairngorm granite, Scotland. Mineral. Mag. 52, 659-67.CrossRefGoogle Scholar
Hodges, K. V. and Royden, L. (1984) Geological thermobarometry of retrograded metamorphic rocks: an indication of the uplife trajectory of a portion of the northern Scandinavian Caledonides. J. Geophys. Res. 89, 7077-90.CrossRefGoogle Scholar
Joesten, R. (1986a) The role of magmatic reaction, diffusion and annealing in the evolution of coronitic microstructure in troctolitic gabbro from Risor, Norway. Mineral. Mag. 50, 441-467.CrossRefGoogle Scholar
Joesten, R. (1986b) The role of magmatic reaction, diffusion and annealing in the evolution of coronitic microstructure in troctolitic gabbro from Risor, Norway: reply. Ibid. 50, 474-9.CrossRefGoogle Scholar
Kontak, D. J. and Corey, M. (1988) Metasomatic origin of spessartine-rich garnet in the South Mountain batholith, Nova Scotia. Can. Mineral. 26, 315-34.Google Scholar
Leake, B. E. (1978) Nomenclature of amphiboles. Mineral. Mag. 42, 533-63.CrossRefGoogle Scholar
Mall, A. P. and Sharma, R. S. (1988) Coronas in olivine metagabbros from the Proterozoic Chotanagpur terrain at Mathurapur, Bihar, India. Lithos, 21, 291–300.CrossRefGoogle Scholar
Manna, S. S. and Sen, S. K. (1974) Origin of garnet in the basic granulites around Saltora, W. Bengal, India. Contrib. Mineral. Petrol. 44, 195-218.CrossRefGoogle Scholar
Manning, D. A. C. (1983) Chemical variation in garnets from aplites and pegmatites, peninsular Thailand. Mineral. Mag. 47, 353-8.CrossRefGoogle Scholar
Mart, R. A. (1989) Petrography of a Grenvillian, coronitic charnockite, western Newfoundland. Unpubl. Honours thesis, Saint Mary's University, 41 pp.Google Scholar
Martignole, J. and Schrijver, K. (1973) Effect of rock composition on appearance of garnet in anorthosite-charnockite suites. Can. J. Earth Sci. 10, 1132-9.CrossRefGoogle Scholar
Miller, C. F. and Stoddard, E. F. (1978) Origin of garnet in granitic rocks: an example of the role of Mn from the Old Woman-Piute Range, California. Geol. Assoc. Amer. Abs. with Prog. 10, 456.Google Scholar
Miller, C. F. and Stoddard, E. F. (1981) The role of manganese in the paragenesis of magmatic garnet: an example from the Old Woman Piute range, California. J. Geol. 89, 233-46.CrossRefGoogle Scholar
Newton, R. C. (1983) Geobarometry of high-grade metamorphic rocks. Amer. J. Sci. 283A, 1–28.Google Scholar
Newton, R. C. and Perkins, D. (1982) Thermodynamic calibration of geobarometers based on the assemblage garnet-plagioclase-orthopyroxene(-clinopyroxene)-quartz. Amer. Mineral. 67, 203-22.Google Scholar
Owen, J. V. (1988) Geochemical changes accompanying the mylonitization of diverse rock types from the GrenvilLe Front zone, eastern Labrador. Can. J. Earth. Sci. 25, 1472-84.CrossRefGoogle Scholar
Owen, J. V. (in press) Geology of the Long Range Inlier, New-foundland. Geol. Surv. Canada Bull. 395.Google Scholar
Owen, J. V. and Erdmer, P. (1989) Metamorphic geology and regional geothermobarometry of a Grenvillian massif: the Long Range Inlier, Newfoundland. Precambrian Res. 43, 7-100.Google Scholar
Owen, J. V. and Erdmer, P. (in press) Middle Proterozoic geology of the Long Range Inlier, Newfoundland: regional significance and tectonic implications. In Mid-Proterozoic Geology of the Southern Margin of Proto-Laurentia-Baltica (Gower, C. F., Rivers, T. and Ryan, A. B., eds.) Geol. Assoc. Canada, Special Volume.Google Scholar
Perkins, D. and Chipera, S. J. (1985) Garnet-orthopyroxene-plagioclase-quartz barometry: refinement and application to the English River sub-province and the Minnesota River valley. Contrib. Mineral. Petrol. 89, 69-80.CrossRefGoogle Scholar
Plank, T. (1987) Magmatic garnets from the Cardigan pluton and the Acadian thermal event in southwest New Hampshire. Amer. Mineral. 72, 681-8.Google Scholar
Rietmeijer, F. J. M. (1979) Pyroxenes from iron-rich igneous rocks in Rogaland, SW. Norway. Geol. Ultraiectina, 21, 341 pp.Google Scholar
Rietmeijer, F. J. M. (1983) Chemical distinction between igneous and metamorphic orthopyroxenes especially those coexisting with Ca-rich clinopyroxenes: a re-evaluation. Mineral. Mag. 47, 143-51.CrossRefGoogle Scholar
Robinson, P., Spear, F. S., Schumacker, J. C., Laird, J., Klein, C., Evans, B. W. and Doolan, B. L. (1982) Phase relations of metamorphic amphiboles: natural occurrence and theory. In Amphiboles: Petrology and experimental phase relations (Veblen, D. R. and Ribbe, P. H., eds.) Mineral. Soc. Amer. Reviews in Mineralogy, 9B, 1–227.Google Scholar
Schneider, G. (1975) Experimental replacement of garnet by biotite. Neues Jahrb. Mineral. Mh., 1-10.Google Scholar
Sen, G. (1985) Experimental determination of pyroxene compositions in the system CaO–MgO–Al2O3–SiO2 at 900–1200° using Pb and H2O fluxes. Amer. Mineral. 70, 678-95.Google Scholar
Sørensen, K. (1979) Are coronas cooling products. Rapp. Grønlands geol. Unders. 89, 113-4.Google Scholar
Stone, M. (1988) The significance of almandine garnets in the Lundy and Dartmoor granites. Mineral. Mag. 52, 651-8.CrossRefGoogle Scholar
Streckeisen, A. (1976) To each plutonic rock its proper name. Earth Sci. Rev. 13, 1-33.CrossRefGoogle Scholar
Thompson, A. B. (1982) Dehydration melting of pelitic rocks and the generation of H2O-undersaturated granitic liquids. Amer. J. Sci. 282, 1567-95.CrossRefGoogle Scholar
Vennum, W. R. and Meyer, C. E. (1979) Plutonic garnets from the Werner batholith, Lassiter Coast, Antarctic Peninsula. Amer. Mineral. 64, 268-73.Google Scholar
Waters, D. J. (1988) Partial melting and the formation of granulite facies assemblages in Namaqualand, South Africa. J. Metamorphic Geol. 6, 387-404.CrossRefGoogle Scholar
Wells, P. R. A. (1977) Pyroxene thermometry in simple and complex systems. Contrib. Mineral. Petrol. 62, 129-39.CrossRefGoogle Scholar
Wood, B. J. and Banno, S. (1973) Garnet-orthopyroxene and orthopyroxene-clinopyroxene in simple and complex systems. Ibid. 42, 109-24.CrossRefGoogle Scholar