The volcanic margins of the northern Labrador Sea: Insights to the rifting process

Abstract

A new interpretation of seismic reflection data on the continental margin of northern Labrador shows basement structures similar to those observed on other volcanic rifted margins. Seaward dipping reflections, inner flows, volcanic plateaus, and lava deltas are observed on these data. Magnetic chron 27n (∼61 Ma) is coincident with the volcanic plateaus, connecting these features to the Paleocene volcanism farther north in Davis Strait. Therefore, we are able to extend the region of volcanism about 500 km south along the margin. Similar structures are also observed on the conjugate west Greenland margin. Below the volcanic plateaus, gravity and wide‐angle seismic data show thick igneous crust, which is fairly symmetrically distributed across the conjugate margins. However, the geometry of the thinned continental crust is not symmetrical: a narrower zone of thinning is observed off northern Labrador. The thick igneous crust lies seaward of thinned continental crust, which exhibits little or no underplating by the magmatic event. This observation is compatible with recent models for the formation of nonvolcanic margins, followed by a magmatic event late in the rift evolution. In Mesozoic time rifting of the cold, thick cratonic lithosphere occurred between Greenland and North America with minimal volcanic activity. Then in Late Cretaceous time, the zone of rifting narrowed and localized seaward of the shelf, creating a relatively narrow zone of lower lithospheric thinning and mantle upwelling into which the Paleocene magmas were eventually channeled. This scenario is supported by studies of Mesozoic igneous rocks on land in coastal west Greenland and Labrador.