Granulite-facies P-T-t paths and the influence of retrograde cation diffusion during polyphase orogenesis, western Grenville Province, Québec
Published:January 01, 2004
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Katherine J.E. Boggs, Louise Corriveau, 2004. "Granulite-facies P-T-t paths and the influence of retrograde cation diffusion during polyphase orogenesis, western Grenville Province, Québec", Proterozoic Tectonic Evolution of the Grenville Orogen in North America, Richard P. Tollo, James McLelland, Louise Corriveau, Mervin J. Bartholomew
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The Bondy gneiss complex preserves evidence of an early 1.20–1.18 Ga granulite-facies tectonometamorphic event within the Central Metasedimentary Belt of Québec, western Grenville Province. Peak metamorphic conditions, estimated with garnet-biotite, garnet-orthopyroxene, garnet-aluminosilicate-quartz-plagioclase, and Al-in-orthopyroxene thermobarometers, reached 950 °C and 10 kilobars, compatible with the presence of sillimanite with orthopyroxene in aluminous gneiss. Peak pressure occurred at 1.20 Ga and was followed by crystallization of peak temperature anatec-tic melt at 1.18 Ga and isothermal decompression as recorded by garnet-cordierite-orthopyroxene-bearing leucosomes and garnet zonation profiles and textures. These conditions are 150–200 °C and 2 kilobars higher than those previously documented in the region. Peak assemblages were overprinted in the Nominingue-Chénéville deformation zone, to the east of the Bondy gneiss complex, during deformation at amphi-bolite facies and intrusion of monzonite-diorite-gabbro sheets at 1.17–1.16 Ga. High concentrations of ferromagnesian inclusions in large garnet grains reduced the effective diffusional domain size, which, when combined with retrograde cation diffusion, locally obliterated evidence of peak metamorphic conditions in the gneiss complex. Retrograde cooling paths in the gneiss complex and the deformation zone are distinct, that of the gneiss complex being at least 0.5 kilobar lower at any given temperature.