Tectonostratigraphic and petrogenetic setting of late Mississippian volcanism in eastern Canada

Abstract

In the aftermath of the Middle Devonian Acadian Orogeny, a thick mafic body is inferred to have been emplaced at the base of the crust during development of the Maritimes Basin complex in eastern Canada and is believed to have sourced regional Late Devonian to Mississippian volcanism. By late Mississippian times, volcanism was limited to central New Brunswick and the Magdalen Islands of eastern Quebec. Whereas Late Devonian to early Mississippian mafic volcanism was mainly characterized by subalkaline lavas produced by the high-degree partial melting of a subduction-enriched lithospheric mantle source, late Mississippian volcanism was dominated by alkali mafic lavas produced by the low-degree partial melting of a sublithospheric mantle source that shows no evidence of subduction imprint. Two distinct upper Mississippian volcanic successions were identified in central New Brunswick and are estimated to be separated by ∼7 million years based on U–Pb dates on felsic intervals. They respectively belong to the Cumberland Hill Formation and a new volcanic member of the Hopewell Cape Formation. As they share close geochemical affinities, we interpret both volcanic units as having been derived from the same primary source but from distinct magmatic pulses. Based on the sedimentology of interbedded clastic units as well as available mapping and geophysical data in New Brunswick, we interpret that the upper Mississippian mafic lavas were issued from large NW–SE striking dykes responding to NW–SE compression in a pull-apart basin, whereas less voluminous and more localised felsic rocks were possibly issued from discrete volcanic pipes.