Late Devonian peraluminous granitic plutons in the Canso area, eastern Meguma Terrane, Nova Scotia
DOI :
https://doi.org/10.4138/1636Résumé
Late Devonian granitic rocks are well exposed In coastal outcrops near Canso In the eastern part of the Meguma Terrane. They form numerous, relatively homogeneous plutons of peralumlnous biotite-muscovite granite and minor granodlorlte which are enriched In muscovite, aluminum and alkalis and depleted in biotite and cafemic components relative to comparable rocks in other Meguma Terrane granites such as the South Mountain and Musquodoboit Batholiths. Individual plutons. which crystallized between 371 and 373 Ha based on U-Pb isotopic data, show a variable relationship between composition and relative age of intrusion. This Implies crystallization from two or more separate batches of slightly different magma supplied from below the current level of exposure. Highly felsic, peralumlnous compositions and initial 87Sr/86Sr ratios ranging from 0.703 to 0.709 favour magma derivation from heterogenous intermediate to felsic continental crust containing some pelitic material. Intrusions were emplaced syntectonlcally during the early part of a ductile shearing event related to dextral transcurrent movements in the Cobequid-Chedabucto Fault System. RÉSUMÉ Des roches granltiques tardidévoniennes foment de vastes affleurements littoraux près de Canso, dans la partie orlentale de la Lanière de Meguma, où elles détermlnent des plutons nombreux, relativement homogènes, constitues surtout de granites péralumineux à biotite et muscovite avec quelque granodlorlte, qui sont enrichis en muscovite, aluminium, alcalls et déficitalres en biotite et conposants cafemiques par rapport aux roches semblables des autres granites de la Lanière de Meguma tels que les batholltes de South Kountain et de Musquodoboit. La rnéthode U-Pb atteste d'une criatalllzatlon entre 371 et 373 Ma. La relation entre leur composition et l'âge relatif de leur intrusion varie selon les plutons. On en deduit une cristallizatlon à partlr de deux (ou plus) venues magmatlques diatinctea, legerement différentés et provenant d'un niveau sous-jacent âge l'affleurement actuel. Leur compositions hautenent felslques et péralumineuses ainsi que des rapports inltlaux 87Sr/86Sr s'échelonnant de 0.703 à 0.709 permettent d'envlsager comne provenance magmatique la remobilisation d'une croflte continentale heterogène, lntermédiaire fi felsique, incorporant un apport pelitique quelconque. Les intrusions furent emplacées syntectonlquement durant l'amorce d'un épisode de cisaillement ductil relie à des mouveroents transcourants dextres dans le système de failles de Cobequid-Chedabucto. [Traduit par le journal]Téléchargements
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