Deep seismic reflection data across the conjugate margins of the Labrador Sea

Abstract

A deep seismic reflection transect of the conjugate margins of the Labrador Sea is described, which represents one of the few data sets of this kind. A characteristic reflectivity is ascribed to a 120 km wide ribbon of very thin crust that may be either thinned continental crust, which has perhaps been intruded, or oceanic crust, perhaps modified by the proximity of the continent. Most of the major changes in crustal thickness and in the subsidence and sedimentation patterns on the margins occur landward of these transitional zones, which are found on both margins. An interpretation of these regions as continental in origin is compatible with other seismic observations on the west Greenland margin, but does not match the magnetic anomaly interpretation, which requires the transitional crust to be oceanic in origin. Models that satisfy the gravity anomalies and the subsidence history have been used to assist in interpreting the seismic data. The subsidence models include the effects of decompression melting during lithospheric extension and rifting, and we predict the thickness of igneous crust produced. However, the gravity models suggest that a lower crustal layer may extend farther inland below the Labrador shelf than is predicted by magmatic underplating. The present seismic results, combined with the other geophysical data, are consistent with a pure shear model of lithospheric stretching, with faulting confined to the upper crust. Many of the problems raised by this data set are similar to those identified in comparing the nonvolcanic margin of Iberia with the conjugate Grand Banks margin in the North Atlantic. If the transition zone results from stretching the continental lithosphere, then a large component of the very thin crust there must consist of igneous material formed by melting. Under these conditions a sharp, vertical ocean-continent boundary would be unlikely.Un profil transversal de sismique rCflexion profonde des marges conjugtes de la mer du Labrador est dtcrit, il reprCsente un parmi les rares ensembles de donntes de ce genre. Une rtflectivitt caractkristique est assignee h un ruban, d'une largeur de 120 krn, de crofite trbs mince qui pourrait &tre soit une crobte continentale amincie rCsultant d'une intrusion possible, ou soit une crofite octanique qui aurait pu etre modifite en raison de sa proximitt du continent. GCnCralement, les changements majeurs qui affectent 1'6paisseur de la crobte, la subsidence et les structures ~Cdimentaires sur les marges sont concentrCs du c6tC des terres dans ces zones de transition qui se trouvent sur les deux marges. L'interprCtation de ces rtgions fondte sur une origine continentale est compatible avec d'autres observations sismiques faites sur la marge du Groenland, mais elle est en dtsaccord avec l'interprktation des anomalies magnCtiques qui indiquent que la croiite transitionnelle est d'origine octanique. Les modbles compatibles avec les anomalies gravimttriques et conformes a l'histoire de la subsidence ont Ctt utilists pour aider interprCter les donnke...

Rifted continental margins: The case for depth-dependent extension

“…The defining characteristics of Type I non-volcanic margins (e.g., Iberia-Newfoundland, Péron-Pinvidic and Manatschal, 2009;Van Avendonk et al, 2009;Sibuet and Tucholke, 2013;Sutra et al, 2013) and Labrador-Southern Greenland (Keen et al, 1994(Keen et al, , 2012Chian et al, 1995;Louden and Chian, 1999) conjugate margins (Fig. 1a) are listed below in order of their development.…”

“…Further north, offshore the Torngat Orogen, crust thins from 38 km to less than 10 km over a distance of only 25 km (Funck and Louden, 1999, Line 5E, Fig. 13;Keen et al, 2012). Xenolith studies (e.g.…”

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

“…Transitional crust on a nonvolcanic margin is characterized by the presence of serpentinized peridotite, both under thinned continental crust and between continental and oceanic crust (Pickup et al, 1996). The transitional crust between the continental and oceanic crust is sometimes dominated by grabens and halfgrabens (Chalmers, 1997;Keen et al, 1994) sometimes not (Chian et al, 1995a), whereas the oceanic crust often is characterized by a smoother basement surface (Chalmers, 1997;Keen et al, 1994) with associated linear magnetic anomalies.…”

Tectonostratigraphic evolution of the Labrador margin, Atlantic Canada

“…Keen et al (1994) and Chian et al (1995a, b) described the deep crustal structure across the nonvolcanic southern Labrador margin, off Hopedale Basin. Like other non-volcanic margins, there are three primary regions.…”

“…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.…”