Crustal structure of the Labrador Sea conjugate margin and implications for the formation of nonvolcanic continental margins

Abstract

Wide‐angle seismic studies have determined the detailed velocity structure along a 350‐km‐long profile across the Labrador margin. Combination of this model with a previously published cross section for the southwestern Greenland margin constitutes the first combined conjugate margin study based on seismic velocity structure. The results indicate three distinct zones across the Labrador margin, similar to the structure of the conjugate Greenland margin. Zone 1 represents 27 to 30‐km‐thick continental crust thinning gradually seaward over ∼100 km distance. Farther seaward, zone 2 is 70–80 km wide, characterized by a distinct lower crust, 4–5 km thick, in which velocity increases with depth from 6.4 to 7.7 km/s. Interpretation for this lower crustal block favors an origin by serpentinized peridotite rather than by magmatic under‐plating. Zone 3 represents two‐layered, normal oceanic crust. The cross sections from both margins are reconstructed to an early drift stage at Chron 27. This demonstrates that the serpentinites in zone 2 are symmetrically distributed between previous identifications of Chrons 31 and 33 on both margins. Zone 1 shows a marked asymmetry, with a gradual thinning of continental crust off Labrador contrasted with a rapid thinning off Greenland. The abundant serpentinization of upper mantle peridotite in zone 2 and the asymmetric shape of zone 1 are both probably related to a very slow rate of continental rifting which produced little if any melt.

Margin segmentation of Baffin Bay/Davis Strait, eastern Canada based on seismic reflection and potential field data

“…Tucholke and Fry (1985) showed a greater than 10 km sedimentary thickness in the Saglek Basin. This thickness is consistent with the refraction data from Funck and Louden (1999) and Chian et al (1995b) farther south on the Labrador margin. At the seaward end of the seismic data, basement highs have been interpreted on a few lines, but their possible continuation is unresolved.…”

“…1) are interpreted as non-volcanic (Reid, 1994;Keen and Potter, 1995;Todd and Reid, 1989;Reid and Keen, 1990;Srivastava and Roest, 1999;Chian et al, 1995b;Louden and Chian, 1999;Louden and Lau, 2001;Funck et al, 2004b). Volcanic margins are characterized by highvelocity lower crust, SDRs and an associated magnetic anomaly with the high-velocity lower crust (Holbrook and Kelemen, 1993).…”

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…”

Constraints on Moho depth and crustal thickness in the Liguro-Provençal basin from a 3D gravity inversion: geodynamic implications

“…and the nature of the thin overlying crust is still debated (Chian et al, 1995;Srivastava and Roest, 1995). Further discussion is beyond the scope of this paper, although much could be learned by integrating the Gulf of Lion data into a much broader review of tectonic processes at non-volcanic margins.…”

“…Thin crust overlying a high velocity layer is found on the western margin of Iberia (3-4 km thick above a 7.3 to 7.6 km/s layer, Whitmarsh et al, 1990;Whitmarsh et al, 1993), in the Tagus abyssal Plain (2 km thick above 7.6 km/s layer increasing to 7.9 km/s towards Moho, Pinheiro et al, 1992) and its conjugate Newfoundland margin off Grand Banks (2-3 km thick above 7.2 to 7.7 km/s layer, Reid, 1994), accross Southwest Greenland margin (2.5 km thick above 7.0 to 7.6 km/s layer, Chian and Louden, 1994) and its conjugate Labrador margin (1-2 km thick above a 6.4 to 7.7 km/s layer, Chian et al, 1995) On the southern Newfoundland margin the high velocity body is limited by one or two landward dipping reflectors rising to basement surface seaward and connecting to Moho landward (Keen and de Voogd, 1988;Reid, 1994). The similarity with the T reflector of the Gulf of Lion is striking.…”