Petrology and age of the Lepreau River Dyke, southern New Brunswick, Canada: source of the end-Triassic Fundy Group basalts

A large dyke of quartz tholeiitic gabbronorite has been mapped for 59 km in southern New Brunswick, Canada, between Lepreau River in the northeast and Indian Island in the southwest. Scattered outcrops occur along a positive aeromagnetic lineament, providing a dyke strike of N42[degrees]E overall (segments N30[degrees]E to N72[degrees]E), dips of 80[degrees] to 90[degrees]NNW, and widths of 4 to 30 m. A [new.sup.40]Ar/[.sup.39]Ar plagioclase age of 201.67 6 0.35 Ma for the Lepreau River Dyke is similar to dates for the massive North Mountain Basalt in the Fundy Basin to the east. The dyke is associated with the Ministers Island and Christmas Cove dykes, which are indistinguishable in chemistry, petrology, and probable age, and we regard them as segments of the same co-magmatic dyke system. In addition, their petrology is similar to that of the basalts of the adjacent Early Mesozoic Fundy and Grand Manan basins. We propose that the Lepreau River and associated dykes were sources for the regional basin basalts, which in turn are part of the Central Atlantic Magmatic Province (CAMP) that overlaps the Triassic-Jurassic boundary and associated mass extinction event. Key words: Mesozoic dykes, Central Atlantic Magmatic Province (CAMP), flood basalt, Fundy Basin. Un grand dyke de gabbronorite tholeitique quartzifere a ete cartographie sur une distance de 59 km dans le sud du Nouveau-Brunswick (Canada) entre la riviere Lepreau, au nord-est, et l'ile Indian, au sud-ouest. Des affleurements disperses sont presents le long d'un lineament aeromagnetique positif, qui donnent une orientation globale de N[42.sup.o]E pour le dyke (les differents troncons allant de N30[degrees]E a N72[degrees]E), des pendages de 80[degrees] a 90[degrees] vers le NNO et des largeurs de 4 m a 30 m. Un nouvel [age.sup.40]Ar/[.sup.39]Ar sur plagioclase de 201,67 6 0,35 Ma pour le dyke de la riviere Lepreau est semblable a des ages obtenus pour le basalte massif de North Mountain, dans le bassin de Fundy plus a l'est. Le dyke est associe aux dykes de l'ile Minister et de Christmas Cove, dont la chimie, la petrologie et l'age probable sont essentiellement identiques, et nous estimons qu'ils constituent des troncons d'un meme systeme de dykes comagmatiques. Leur petrologie est en outre semblable a celle des basaltes des bassins de Fundy et de Gand Manan attenants, d'age mesozoique precoce. Nous proposons que le dyke de la riviere Lepreau et les dykes associes constituaient des sources pour les basaltes de bassin regionaux qui, eux, font partie de la province magmatique centre atlantique (PMCA) qui chevauche la limite Trias-Jurassique et l'episode d'extinction massive associe. [Traduit par la Redaction] Mots-cles : dykes mesozoiques, province magmatique centre atlantique (PMCA), basalte de plateau, bassin de Fundy.
Introduction Flood basalts in large igneous provinces are produced by fissure eruptions, which can be exceptionally large (tens to hundreds of kilometres long), and with huge eruption volumes of tens [...]