Observations of anomalous oceanic crust in the Canada Basin, Arctic Ocean

doi:10.1016/0012-821X(95)00108-O

Earth and Planetary Science Letters

Volume 134, Issues 1–2, August 1995, Pages 99-106

https://doi.org/10.1016/0012-821X(95)00108-O Get rights and content

Abstract

We present a seismic reflection frofile and coincident refraction data in deep water north of the Northwind Ridge, in the Canada Basin. The reflection profile shows a package of bright events, which are locally nonparallel and discontinuous, about 2.5 s below the seafloor. These bright reflectors are of interest because previous reflection profiles in the Canada Basin have not penetrated the coherent flat-lying events, which are typical of bedded sedimentary rocks. These prominent reflections are recorded on the refraction profile as wide-angle reflections, and the locally nonparallel and discontinuous event as a refraction. On the refraction profile the nonparallel and discontinuous event exhibits lower frequencies and has an associated refraction with a velocity of 4.5 km/s and a high gradient. This event is interpreted as representing the top of oceanic layer 2, which is observed for the first time in the Canada Basin. Three kilometres beneath layer 2 a velocity of 7.2–7.5 km/s is measured. This layer could represent either a high-velocity layer 3 or serpentinized mantle. Based on comparison with the eastern Grand Banks and the west Iberian and Labrador Sea margins the interpretation of serpentinized mantle is preferred.

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Cited by (5)

Distribution of crustal types in Canada Basin, Arctic Ocean
2016, Tectonophysics
Citation Excerpt :
SB 1014 to the north of these sonobuoys and adjacent to Northwind Ridge has crustal velocities in the range of, 6.0–6.6 km/s overlying 7.4 km/s. SB 1015 slightly to the east records a 6.3 km/s layer overlying a 7.4 km/s refractor with an associated weak PmP arrival. This velocity range of above 7.4–7.5 km/s is compatible with an earlier result of Jackson et al. (1995) in the same area, suggesting that extremely thin, heterogeneous and possibly continental crust is a common character of this transitional zone in deep water near Northwind Ridge. Thirteen sonobuoys are classified as thinned continental crust and most have velocities of 5.5–6.6 km/s with no evidence of a higher velocity 7.2–7.6 km/s deep layer (Fig. 3a).
Seismic velocities determined from 70 sonobuoys widely distributed in Canada Basin were used to discriminate crustal types. Velocities of oceanic layer 3 (6.7–7.1 km/s), transitional (7.2–7.6 km/s) and continental crust (5.5–6.6 km/s) were used to distinguish crustal types. Potential field data supports the distribution of oceanic crust as a polygon with maximum dimensions of ~ 340 km (east–west) by ~ 590 km (north–south) and identification of the ocean–continent boundary (OCB). Paired magnetic anomalies are associated only with crust that has oceanic velocities. Furthermore, the interpreted top of oceanic crust on seismic reflection profiles is more irregular and sometimes shallower than adjacent transitional crust. The northern segment of the narrow Canada Basin Gravity Low (CBGL), often interpreted as a spreading center, bisects this zone of oceanic crust and coincides with the location of a prominent valley in seismic reflection profiles. Data coverage near the southern segment of CBGL is sparse. Velocities typical of transitional crust are determined east of it. Extension in this region, close to the inferred pole of rotation, may have been amagmatic. Offshore Alaska is a wide zone of thinned continental crust up to 300 km across. Published longer offset refraction experiments in the Basin confirm the depth to Moho and the lack of oceanic layer 3 velocities. Further north, toward Alpha Ridge and along Northwind Ridge, transitional crust is interpreted to be underplated or intruded by magmatism related to the emplacement of the High Arctic Large Igneous Province (HALIP). Although a rotational plate tectonic model is consistent with the extent of the conjugate magnetic anomalies that occupy only a portion of Canada Basin, it does not explain the asymmetrical configuration of the oceanic crust in the deep water portion of Canada Basin, and the unequal distribution of transitional and continental crust around the basin.
The nature of oceanic lower crust and shallow mantle emplaced at low spreading rates
1997, Tectonophysics
Thermal calculations indicate that at sea floor spreading rates too low to sustain a steady-state magma chamber, most of the upwelling melt still freezes within ∼10 km of the sea floor beneath a mid-ocean ridge. A thickened lower crustal section containing crust-mantle mix is thus predicted. Reduced melting in the source region is an expected effect of low spreading rates. However, cooling from the surface limits the degree to which mafic crustal material is separated from mantle at spreading rates higher than those at which reduced melting becomes important. Evidence for ultramafic contributions to the crust at low spreading rates includes a distinct seismic velocity profile for crust from very slow ridges, evidence of aging of the lower crust, spreading-rate-dependent differences in reflection seismic structure and character, and seismic crustal thicknesses apparently greater than adiabatic crustal thicknesses. Crustal structure inferred from the thermal results agrees with the model of Cannat [Cannat, M., 1993. Emplacement of mantle rocks in the seafloor at mid-ocean ridges. J. Geophys. Res. 98, 4163–4172], which includes a lower crust of mixed composition achieved without the requirement of gross tectonic rearrangement of an originally stratified crustal section.
Chapter 50: Geology and tectonic development of the Amerasia and Canada Basins, Arctic Ocean
2011, Geological Society Memoir
A new view on the origin of magmatism of the Franz Josef Land
2001, Izvestiya - Physics of the Solid Earth
New K-Ar ages for basalts from Franz Josef land
2001, Russian Journal of Earth Sciences

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Observations of anomalous oceanic crust in the Canada Basin, Arctic Ocean

Abstract

Mar. Geol.

Tectonophysics

Tectonophysics

Cruise report and preliminary results, US Geological Survey Cruise PI-93-AR, Northwind Ridge and Canada Basin, Arctic Ocean, aboard USCGC Polar Star, August 16–September 15, 1993

U.S. Dep. Inter., U.S. Geol. Surv. Open-File Rep. 93-389

Magnetic anomalies

A compilation of magnetic observations from the Arctic and the North Atlantic Ocean and the adjacent landmasses

A seismic refraction experiment in the Beaufort Sea

Bull. Seismol. Soc. Am.

Crustal structure and velocity anisotropy beneath the Beaufort Sea

Can. J. Earth Sci.

Array refraction profiles and crustal models of the Canada Basin

J. Geophys. Res.