Abstracts
Abstract
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 Sr/ Sr ratios ranging from 0.703 to 0.7O9 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.
RESUME
Des roches granltiques tardidevoniennes foment de vastes affleurements llttoraux pres de Canso, dans la partie orlentale de la Laniere de Meguma, ou elles determlnent des plutons nombreux, relativement homogenes, const!tues surtout de granites peralumineux a biotite et muscovite avec quelque granodlorlte, qui sont enrichis en muscovite, aluminium, alcalls et deficitalres en biotite et conposants cafemiques par rapport aux roches semblables des autres granites de la Laniere de Meguma tels que les batholltes de South Kountain et de Musquodoboit. La rnethode U-Pb atteste d'une criatalllzatlon entre 371 et 373 Ma. La relation entre leur composition et l'age relatif de leur intrusion varie selon les plutons. On en deduit une cristallizatlon a partlr de deux (ou plus) venues magmatlques diatinctea, legerement differentea et provenant d'un niveau sous-jacent agl'affleurement actuel. Leur compositions hautenent felslques et peralumineuses alnsl que des rapports inltlaux /Sr/ Sr s'echelonnant de 0.703 a 0.709 permettent d'envlsager comne provenance magmatique la remobilisation d'une croflte continentale heterogene, lntermedlaire fl felsique, incorporant un apport pelitique quelconque. Les intrusions furent emplacees syntectonlquement durant l'amorce d'un episode de cisaillement ductil relie a des mouveroents transcourants dextres dans le system* de failles de Cobequid-Chedabucto.
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