Formation of the Volcanic Margins of West Greenland and North-Eastern Canada*

On the West Greenland and North-Eastern Canadian margins, as with many other volcanic passive margins (VPMs), a mantle plume has been proposed to elevate mantle temperatures sufficiently to account for the large volumes of magmatism observed. A number of observations made on both of these margins have been attributed to the passage of a mantle plume beneath this region (120-60Ma). Observations include the initiation of seafloor spreading in the Labrador Sea and Baffin Bay; the presence of large volumes of both extrusive and intrusive magmatism; the interpretation of seaward dipping reflectors (SDRs); the modelled underplating of the Davis Strait by a high-velocity body; and the presence of high 3He/4He ratios in picrites. The presence and role of mantle plumes during the formation of VPMs remains equivovcal, and cannot explain many of the larger scale features observed on the West Greenland and North-Eastern Canadian margins. Here we consider potential spatial and temporal mismatches between proposed hotspot track locations and independently dated geological events observed on the West Greenland and North-Eastern Canadian margins. These mismatches include; the timing of seafloor spreading initiation; location of seafloor spreading and the presence of ‘pre-plume’ coast parallel dyke swarms. These observations lead us to propose that the mantle plume hypothesis alone cannot satisfactorily explain the formation of all the geological features observed along these margins and that alternative mechanism(s) should be considered. Understanding the fundamental mechanisms involved in the formation of volcanic passive margins is critical in the reduction of exploration risk on such margins, as they place constraints on the structural and thermal evolution of the margin. This is particularly relevant as exploration activity extends further into frontier regions such as the West Greenland margin. Forma on of the volcanic margins of West Greenland and North-Eastern Canada: Background and Ra onale Alex Peace, Ken McCaffrey, Jonny Imber, Jeroen van Hunen, Richard Hobbs and Keith Gerdes 1 Department of Earth Sciences, Science Laboratories, Durham University, Durham, UK, DH1 3LE 2 Shell Interna onal Explora on and Produc on B.V, Carel van Bylandtlaan 5, 2596 HP Den Haag, The Netherlands Contact email: a.l. peace@durham.ac. uk The Plume theory in West Greenland The mantle plume theory is the most common mechanism proposed in the literature as an explana on for the forma on of the volcanic margins of West Greenland and North-Eastern Canada (e.g. Chalmers, 1995). Observa ons a ributed to a Mantle Plume in Greenland: Onset of seafloor spreading in the Labrador Sea (Chalmers and Larsen, 1995; Gerlings et al., 2009). Major volcanism in West Greenland and Baffin Island (Chalmers and Larsen, 1995; Storey et al., 1998). Underpla ng of the Davis Strait by a high-velocity body (Gerlings et al., 2009). High He/He (Graham et al., 1998) and low Os/Os ra os in Picrites (Schaefer et al., 2000). Upli of onshore sedimentary successions (Dam et al., 1998). High mel ng temperatures for picrites (Gill et al., 1992). Seismically observable volcanics for 400km east of Baffin Island (Funck et al., 2007).