Seismic evidence for plume-derived volcanism during formation of the continental margin in southern Davis Strait and northern Labrador Sea

Abstract

SUMMARY The crustal structure in the southern Davis Strait and the adjacent ocean–continent transition zone in NE Labrador Sea was determined along a 185‐km‐long refraction/wide‐angle reflection seismic transect to study the impact of the Iceland mantle plume to this region. A P‐wave velocity model was developed from forward and inverse modelling of dense airgun shots recorded by ocean bottom seismographs. A coincident industry multichannel reflection seismic profile was used to guide the modelling as reflectivity could be identified down to Moho. The model displays a marked lateral change of velocity structure. The sedimentary cover (velocities 1.8–3.9 km s−1) is up to 4 km thick in the north and thins to 1 km in the south. The segment of the line within southern Davis Strait is interpreted to be of continental character with a two‐layered 13‐km‐thick crust with P‐wave velocities of 5.6–5.8 and 6.4–6.7 km s−1 in the upper and lower crust, respectively. The crust is underlain by a 2‐ to 4‐km‐thick high‐velocity layer (7.5 km s−1). This layer we interpret as underplated material related to the Iceland plume. The southern segment of the line in Labrador Sea displays a 2‐km‐thick layer with a velocity of 4.5 km s−1. This layer can be correlated to a well about 100 km to the west of the line, where Palaeocene basalts and interbedded sediments were drilled. Underneath is a 12‐km‐thick crust with a 2‐km‐thick upper layer (5.8–6.6 km s−1) and a 10‐km‐thick lower layer (6.8–7.2 km s−1). This crust is interpreted to be of oceanic character. S‐wave modelling yields a Poisson's ratio of 0.28 for the lower crust, compatible with a gabbroic composition. The igneous crust is 5 km thicker than normal oceanic crust. We suggest that the increased magma production was created by buoyancy‐driving flow. We propose a model in which initial seafloor spreading occurred between Labrador and West Greenland, when the Iceland plume arrived in the area at ∼62 Ma and caused enhanced magma production. Shortly afterwards (chron 27–26), plume material was channelled southward underplating part of Davis Strait and forming basaltic flows interbedded with sediment.

Tectonostratigraphic evolution of the Labrador margin, Atlantic Canada

“…The margins of the Labrador Sea have been classified as nonvolcanic (Chian et al, 1995a, b) although there has been significant flood basalt overprinting of non-volcanic structures in the northern regions bordering the Davis Strait (Chalmers, 1997;Chalmers and Pulvertaft, 2001;Skaarup et al, 2006;Funck et al, 2007;Gerlings et al, 2009). Keen et al (1994) and Chian et al (1995a, b) described the deep crustal structure across the nonvolcanic southern Labrador margin, off Hopedale Basin.…”

“…Srivastava, 1978;Umpleby, 1979;McWhae, 1981;Balkwill, 1987;Bell, 1989;Moir, 1989;Balkwill and McMillan, 1990;Enachescu, 2006aEnachescu, ,b, 2008Dickie et al, 2009). Significant advances elucidating the deep structure of the Labrador continental margin (Keen et al, 1994;Chian et al, 1995a, b;Srivastava and Roest, 1999;Funck et al, 2007;Gerlings et al, 2009) have been pivotal in documenting the complex structure and tectonic evolution of the Labrador Sea region and that of non-volcanic margins globally (Peron-Pinvidic and Manatschal, 2008;Reston, 2009). In addition, the Labrador Sea provides an important oceanographic connection between the Arctic and Atlantic oceans.…”

Moho and basement depth in the NE Atlantic Ocean based on seismic refraction data and receiver functions

“…Hence, there might be out-of-plane phases mimicking a Moho. Alternatively, the deep Moho could be an intra-mantle reflection similar to the one observed off West Greenland (Gerlings et al 2009) in an area that was affected by the Iceland plume. The depth at the top of the high-velocity zone (7.5 km s 21 ) on DLC 94 line 5 varies between 26 and 34 km, and would, in fact, be in reasonable agreement with the interpreted Moho on SIGMA lines 3 and 4.…”

Evolution of the west Greenland margin: offshore thermostratigraphic data and modelling

“…The oldest Palaeocene volcanic rocks dated from the region are basalts dredged from the Davis Strait with an age of 63.0 Ma and a geochemistry that indicates formation beneath a strongly attenuated continental lithospheric lid (Larsen & Dalhoff 2006;Larsen et al 2009). Chalmers & Laursen (1995) concluded, therefore, that sea-floor spreading started in the Labrador Sea during the Palaeocene coevally with the arrival of the 'Iceland plume' (Funck et al 2007;Gerlings et al 2009), major volcanism in central west Greenland (Dalhoff et al 2003) and the outpouring of basaltic lavas on SE Baffin Island. Nielsen et al (2007) suggested that these events are related to plate reorganizations and regional stress modifications in the Greenland-Eurasian plate at this time and not necessarily to the impingement of a mantle plume.…”