Crustal structure of the central Nova Scotia margin off Eastern Canada

Abstract

S U M M A R YThe central Nova Scotia margin off Eastern Canada is located at a transition from a volcanic margin in the south to a non-volcanic margin in the north. In order to study this transition, a wide-angle refraction seismic line with dense airgun shots was acquired across the central Nova Scotia margin. The 500-km-long transect is coincident with previous deep reflection profiles across the Lahave Platform and extending into the Sohm Abyssal Plain. A P-wave velocity model was developed from forward and inverse modelling of the wide-angle data from 21 ocean bottom seismometers and coincident normal-incidence reflection profiles. The velocity model shows that the continental crust is divided into three layers with velocities of 5.5-6.9 km s −1 . The maximum thickness is 36 km. A minor amount (∼5 km) of thinning occurs beneath the outer shelf, while the major thinning to a thickness of 8 km occurs over the slope region. The seaward limit of the continental crust consists of 5-km-thick highly faulted basement. There is no evidence for magmatic underplating beneath the continental crust. On the contrary, a 4-km-thick layer of partially serpentinized mantle (7.6-7.95 km s −1 ) begins beneath the highly faulted continental crust, and extends ∼200 km seawards, forming the lower part of the oceancontinent transition zone. The upper part of the transition zone consists of the highly faulted continental crust and 4-to 5-km-thick initial oceanic crust. The continent-ocean boundary is moved ∼50 km farther seawards compared to an earlier interpretation based only on reflection seismic data. The oceanic crust in the transition zone consists of layer 2 and a high-velocity lower crustal layer. Layer 2 is 1-3 km thick with velocities of 5.6-6.0 km s −1 . The high-velocity lower crustal layer is 1-2 km thick with velocities of 7.25-7.4 km s −1 , suggesting a composite layer of serpentinized peridotite and gabbroic layer 3. Oceanic crust with normal thickness of 5-7 km and more typical layer 3 with velocities of 6.95-7.3 km s −1 is observed at the seaward end of the profile.

Deep crustal structure of the North-West African margin from combined wide-angle and reflection seismic data (MIRROR seismic survey)

“…While the Nova Scotia margin has been subject to numerous marine geophysical studies (e.g. Funck et al, 2004;Wu et al, 2006), the conjugate African segment remains fairly unknown, except for the northernmost segment (Holik et al, 1991;Contrucci et al, 2004;Jaffal et al, 2009;Klingelhoefer et al, 2009).…”

An investigation of salt tectonic structural styles in the Scotian Basin, offshore Atlantic Canada: 1. Comparison of observations with geometrically simple numerical models

“…To first order, the large-scale synrift geometry of a rifted margin will depend on the distribution of lithospheric extension across the margin. In designing the models we assume that (1) lithospheric extension is uniform with depth, (2) the extension varies across the 200 km margin in an approximately linear manner that is consistent with crustal models developed by Keen and Potter [1995], Funck et al [2004], and Wu et al [2006], and (3) the stretched margin is in isostatic equilibrium in a configuration determined by the thickness, density and thermal state of the extended lithosphere. Synrift salt and clastic sediments load the margin and the system is flexurally isostatically balanced in a submarine configuration including loading by the water.…”

“…We chose h cc = 35 km, h oc = 6.5 km, and densities r cc = r oc = 2860 kg m −3 , and r cm = r om = 3225 kg m −3 , which allows the depth of the top of the oceanic crust to be calculated. Corresponding depths across the margin, assumed to be 200 km wide between positions X 1 and X 2 (a geometry consistent with recent seismic refraction surveys [Keen and Potter, 1995;Funck et al, 2004;Wu et al, 2006]), are calculated by linear interpolation because the lithosphere is assumed to thin linearly across the margin.…”

Evolution of deep‐water rifted margins: Testing depth‐dependent extensional models

“…These results, and those in Appendix B, show that for most well-imaged nonvolcanic margins, a simple isostatic model based on a constant crustal density adequately describes the final subsidence of the margin as a function of crustal thinning and is a justification for the modeling we discuss in this paper. Data references are Horsefield et al [1994], Lau et al [2006], Wu et al [2006], Moulin et al [2005], Nissen et al [1995a], and Schnabel et al [2008]. [10] In conjunction with equation (1), this second rule provides an important pin which constrains paleobathymetry at the distal end of a continental margin where estimates are usually poorest.…”

“…Figure B5. Data sources as follows: Nova Scotia [Wu et al, 2006], East Coast U.S. [Lizzaralde et al, 1997], N Morocco [Contrucci et al, 2004], SW Morocco , Surinam [Greenroyd et al, 2008], and French Guyana [Greenroyd et al, 2007]. Figure B6.…”