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

Abstract

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°E overall (segments N30°E to N72°E), dips of 80° to 90°NNW, and widths of 4 to 30 m. A new 40Ar/39Ar plagioclase age of 201.67 ± 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.