The crustal structure of southern Baffin Bay: implications from a seismic refraction experiment

Abstract

SUMMARY Baffin Bay represents the northern extension of the extinct rift system in the Labrador Sea. While the extent of oceanic crust and magnetic spreading anomalies are well constrained in the Labrador Sea, no magnetic spreading anomalies have yet been identified in Baffin Bay. Thus, the nature and evolution of the Baffin Bay crust remain uncertain. To clearly characterize the crust in southern Baffin Bay, 42 ocean bottom seismographs were deployed along a 710‐km‐long seismic refraction line, from Baffin Island to Greenland. Multichannel seismic reflection, gravity and magnetic anomaly data were recorded along the same transect. Using forward modelling and inversion of observed traveltimes from dense airgun shots, a P‐wave velocity model was obtained. The detailed morphology of the basement was constrained using the seismic reflection data. A 2‐D density model supports and complements the P‐wave modelling. Sediments of up to 6 km in thickness with P‐wave velocities of 1.8–4.0 km s−1 are imaged in the centre of Baffin Bay. Oceanic crust underlies at least 305 km of the profile. The oceanic crust is 7.5 km thick on average and is modelled as three layers. Oceanic layer 2 ranges in P‐wave velocity from 4.8 to 6.4 km s−1 and is divided into basalts and dykes. Oceanic layer 3 displays P‐wave velocities of 6.4–7.2 km s−1. The Greenland continental crust is up to 25 km thick along the line and divided into an upper, middle and lower crust with P‐wave velocities from 5.3 to 7.0 km s−1. The upper and middle continental crust thin over a 120‐km‐wide continent–ocean transition zone. We classify this margin as a volcanic continental margin as seaward dipping reflectors are imaged from the seismic reflection data and mafic intrusions in the lower crust can be inferred from the seismic refraction data. The profile did not reach continental crust on the Baffin Island margin, which implies a transition zone of 150 km length at most. The new information on the extent of oceanic crust is used with published poles of rotation to develop a new kinematic model of the evolution of oceanic crust in southern Baffin Bay.

Crust and Lithospheric Structure - Global Crustal Structure

“…Depth ( Barazangi and Brown 1986a,b Barton and White 1997Becker et al 2012Blundell and Raynaud 1986Breivik et al 2003Broucher 1995Bullock and Minshull 2005Chian et al 1995Christeson et al 2008Clegg and England 2003Clowes et al 1999Clowes et al 1987 Pavlenkova et al 2009Prajapati et al 2011Qiu et al 2001Ritzmann et al 2002Roberts et al 1988Rubio et al 2000Sage et al 2000Stankiewicz et al 2008Suckro et al 2012Thréhu et al 1994Tkalcic et al 2011Toomey et al 2007Todd et al 1988Torne et al 2003Vuan et al 2005Wang et al 2004a,b Watremez et al 2011White and McKenzie 1989White and Smith 2009White et al 1987a,b Worthington et al 2012…”

Tectonic variation and structural evolution of the West Greenland continental margin

“…............... 48 , Funck et al (2007Funck et al ( , 2012, and Suckro et al (2012Suckro et al ( , 2013. Serpentinite zone from Nafe-Drake polynomial curve was interpreted in Baffin Bay, , Funck et al (2007Funck et al ( , 2012, and Suckro et al (2012Suckro et al ( , 2013. Serpentinite zone from Nafe-Drake polynomial curve was interpreted in Baffin Densities were then calculated as a function of velocities using four different methods and in comparison with published data of , Funck et al (2007Funck et al ( , 2012, and Suckro et al (2012Suckro et al ( , 2013.…”

“…New COT boundaries have been interpreted based on multidisciplinary data integration of seismic reflection, refraction interpretation, gravity, magnetic 2D modelling and backstripping thermal subsidence modelling. ............... 48 , Funck et al (2007Funck et al ( , 2012, and Suckro et al (2012Suckro et al ( , 2013. Serpentinite zone from Nafe-Drake polynomial curve was interpreted in Baffin Bay, , Funck et al (2007Funck et al ( , 2012, and Suckro et al (2012Suckro et al ( , 2013.…”

“…Serpentinite zone from Nafe-Drake polynomial curve was interpreted in Baffin Bay, , Funck et al (2007Funck et al ( , 2012, and Suckro et al (2012Suckro et al ( , 2013. Serpentinite zone from Nafe-Drake polynomial curve was interpreted in Baffin Densities were then calculated as a function of velocities using four different methods and in comparison with published data of , Funck et al (2007Funck et al ( , 2012, and Suckro et al (2012Suckro et al ( , 2013. Serpentinite zone from Nafe-Drake polynomial curve was interpreted in Baffin Bay, Figure 6.1: Regional tectonic framework of the west Greenland area generated by data integration of 2D seismic data (GEUS), structural provinces after Knutsen et al, (2012), seafloor data from Müller 2008, Global Seafloor Fabric and Magnetic chrons from Roest and Srivastava 1989;and Chalmers and Laursen (1995 shear-simple shear model (Lister et al, 1986), have described how crustal attenuation, followed by thermal subsidence and isostatic compensation have played the key roles in lithospheric and mantle geodynamics.…”

Reflection/Refraction Seismology

“…Intra-crustal reflection interfaces are deciphered from analyses of amplitude characteristics in wide-angle reflection and refraction records. Being a powerful tool in the studies of continent-ocean boundaries, refraction surveying and the resulting velocity-depth models have revealed that these boundaries are often transitional zones of various widths in continental margins of both volcanic and non-volcanic types (e.g., Mjelde et al, 2005;Voss and and Jokat, 2007;Suckro et al, 2012). While the normal-incidence seismic reflection technique largely fails to properly image sub-salt and sub-basalt sedimentary formations and structures, the seismic refraction technique is used as a complimentary tool to provide velocity information from such "hidden" zones.…”