SHRIMP U-Pb zircon geochronology of the Bondy gneiss complex: Evidence for circa 1.39 Ga arc magmatism and polyphase Grenvillian metamorphism in the Central Metasedimentary Belt, Grenville Province, Québec
Published:January 01, 2004
Natasha Wodicka, Louise Corriveau, Richard A. Stern, 2004. "SHRIMP U-Pb zircon geochronology of the Bondy gneiss complex: Evidence for circa 1.39 Ga arc magmatism and polyphase Grenvillian metamorphism in the Central Metasedimentary Belt, 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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We report sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon ages from high-grade gneisses of the Bondy gneiss complex, a volcano-plutonic arc and back-arc edifice hosting a Cu-Au-Fe oxides hydrothermal system in the Central Metasedimentary Belt, Grenville Province, Québec. Samples of quartzofeldspathic gneiss gave broadly similar results, with zircon cores indicating ages between 1.59 and 1.21 Ga and mantles or whole new zircon crystals giving Grenvillian metamorphic ages. A few analyses indicate minor involvement of Paleoproterozoic and Archean crustal material. Zircon cores are interpreted to have grown during crystallization of the quartzofeldspathic gneiss protoliths, but precise ages could not be determined for any of the samples. The spread of ages is attributed mainly to isotopic disturbance owing to hydrothermal alteration, high-pressure-temperature (P-T) metamorphism, and/or recent Pb loss. Only a sample of tonalitic gneiss yielded a well-defined, igneous crystallization age of 1386 ± 10 Ma. Younger zircons from the dated lithologies provide evidence for two episodes of Grenvillian metamorphism: a period of high-P-T granulite-facies metamorphism and partial melting at 1.21–1.18 Ga, and a younger, albeit localized, metamorphic overprint at ca. 1.15–1.13 Ga.
The new SHRIMP U-Pb data indicate that the composite volcano-plutonic edifice likely formed, at least in part, at ca. 1.39 Ga. Together with recently published geochemical and Nd data, the new data (1) extend the known distribution of ca. 1.39 Ga arc-related magmatism in the Grenville Province, and (2) suggest that a major portion of the source region to the Bondy gneiss complex was produced by the addition of voluminous juvenile Mesoproterozoic material.