Full-fit reconstruction of the Labrador Sea and Baffin Bay

M Hosseinpour,S E Williams,J M Whittaker,R D Müller

doi:10.5194/se-4-461-2013

Abstract

Abstract. Reconstructing the opening of the Labrador Sea and Baffin Bay between Greenland and North America remains controversial. Recent seismic data suggest that magnetic lineations along the margins of the Labrador Sea, originally interpreted as seafloor spreading anomalies, may lie within the crust of the continent–ocean transition. These data also suggest a more seaward extent of continental crust within the Greenland margin near Davis Strait than assumed in previous full-fit reconstructions. Our study focuses on reconstructing the full-fit configuration of Greenland and North America using an approach that considers continental deformation in a quantitative manner. We use gravity inversion to map crustal thickness across the conjugate margins, and assimilate observations from available seismic profiles and potential field data to constrain the likely extent of different crustal types. We derive end-member continental margin restorations following alternative interpretations of published seismic profiles. The boundaries between continental and oceanic crust (COB) are restored to their pre-stretching locations along small circle motion paths across the region of Cretaceous extension. Restored COBs are fitted quantitatively to compute alternative total-fit reconstructions. A preferred full-fit model is chosen based on the strongest compatibility with geological and geophysical data. Our preferred model suggests that (i) the COB lies oceanward of magnetic lineations interpreted as magnetic anomaly 31 (70 Ma) in the Labrador Sea, (ii) all previously identified magnetic lineations landward of anomaly 27 reflect intrusions into continental crust and (iii) the Ungava fault zone in Davis Strait acted as a leaky transform fault during rifting. This robust plate reconstruction reduces gaps and overlaps in Davis Strait and suggests that there is no need for alternative models proposed for reconstructions of this area including additional plate boundaries in North America or Greenland. Our favoured model implies that break-up and formation of continent–ocean transition (COT) first started in the southern Labrador Sea and Davis Strait around 88 Ma and then propagated north and southwards up to the onset of real seafloor spreading at 63 Ma in the Labrador Sea. In Baffin Bay, continental stretching lasted longer and actual break-up and seafloor spreading started around 61 Ma (chron 26).

Highlights

The Labrador Sea and Baffin Bay formed following Cretaceous rifting between Greenland and North America (Fig. 1)
Existing reconstruction models for the relative positions of Greenland and North America during Cretaceous continental rifting include those of Bullard et al (1965), Rowley and Lottes (1988), Srivastava and Roest (1989) and Dunbar and Sawyer (1989) These reconstructions were derived under assumptions that much of the crust in the continent–ocean transition (COT) was oceanic during chron 28–31 time (70–64 Ma according to timescale from Gradstein et al, 2012) and that
The most dramatic differences in the position of the restored COB (RCOB) occur in the Greenland margin in the northern Labrador Sea near Davis Strait

Summary

Introduction

The Labrador Sea and Baffin Bay formed following Cretaceous rifting between Greenland and North America (Fig. 1). Existing reconstruction models for the relative positions of Greenland and North America during Cretaceous continental rifting include those of Bullard et al (1965), Rowley and Lottes (1988), Srivastava and Roest (1989) and Dunbar and Sawyer (1989) These reconstructions were derived under assumptions that much of the crust in the continent–ocean transition (COT) was oceanic during chron 28–31 time (70–64 Ma according to timescale from Gradstein et al, 2012) and that. Hosseinpour et al.: Full-fit reconstruction of the Labrador Sea and Baffin Bay spreading anomalies could be used to constrain relative plate motions (Roest and Srivastava, 1989) This appears questionable in the light of subsequently collected seismic data, yet the anomaly identifications and reconstructions derived from these interpretations are still used within global-scale compilations (Torsvik et al, 2008; Müller et al, 2008; Seton et al, 2012). More recent reconstruction models only consider seafloor spreading since chron 27 (63 Ma), the earliest undebated spreading anomalies (Oakey, 2005; Oakey and Chalmers, 2012)

Methods

Results

Discussion

Conclusion