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Seismic velocity structure of the rifted margin of the eastern Grand Banks of Newfoundland, Canada

Seismic velocity structure of the rifted margin of the eastern Grand Banks of Newfoundland, Canada
Seismic velocity structure of the rifted margin of the eastern Grand Banks of Newfoundland, Canada
We present a compressional seismic velocity profile of the crust of the eastern margin of the Grand Banks of Newfoundland, Canada. This velocity model was obtained by a tomographic inversion of wide-angle data recorded on a linear array of 24 ocean bottom seismometers (OBSs). At the landward side, we imaged a crustal thickness of 27 km in Flemish Pass and beneath Beothuk Knoll, which is thinner than the 35-km-thick crust of the central Grand Banks. We therefore assume that the eastern rim of the Grand Banks stretched uniformly by 25%. Farther seaward, the continental crust tapers rapidly beneath the continental slope to ?6 km thickness. In the distal margin we find a 60-km-wide zone with seismic velocities between 5.0 and 6.5 km s?1 that thins to the southeast from 6 to 2 km, which we interpret as highly extended continental crust. Contrary to other seismic studies of the margins of the Grand Banks, we find seismic velocities of 8 km s?1 and higher beneath this thin crustal layer in the continent-ocean transition. We conclude that mantle was locally emplaced at shallow levels without significant hydration from seawater or serpentinized mantle was removed along a décollement in the final stages of continental rifting. The outer edge of highly extended continental crust borders a 25-km-wide zone where seismic velocities increase gradually from 6.3 km s?1 just below the top of acoustic basement to 7.7 km s?1 at 5 km below basement. We interpret this area as a relatively narrow zone of exhumed and serpentinized continental mantle. Seaward, we imaged a thin and laterally heterogeneous layer with a seismic velocity that increases sharply from 5.0 km s?1 in basement ridges to 7.0 km s?1 at its base, overlying mantle velocities between 7.8 and 8.2 km s?1. We interpret this area as unroofed mantle and very thin oceanic crust that formed at an incipient, magma-starved, ultraslow spreading ridge. A comparison of the conjugate rifted margins of the eastern Grand Banks and the Iberia Abyssal Plain show that they exhibit a similar seaward progression from continental crust to mantle to oceanic crust. This indicates that before continental breakup, rifting exhumed progressively deeper sections of the continental lithosphere on both conjugate margins. A comparison between the continent-ocean transition of the Grand Banks and Flemish Cap shows that the final phase of continental rifting and the formation of the first oceanic crust required more time at the Grand Banks margin than at the southeastern margin of Flemish Cap.
continental rifting, marine geophysics, passive margin
0148-0227
B11404
Van Avendonk, Harm J.A.
a8ed08ac-3232-480f-8760-bc7ee1edfbd0
Holbrook, W. Steven
639d0174-f356-4910-a394-c46a2ccb2919
Nunes, Gregory T.
23d0261a-dbcd-4bf4-b8b7-33a7b1bed314
Shillington, Donna J.
e53cb591-7124-4886-88a5-1b92f65fb199
Tucholke, Brian E.
284cd485-2bca-4494-829f-2fe592df96a8
Louden, Keith E.
b818fc43-6f0c-4cbd-99d1-3c60db40e9e8
Larsen, Hans Christian
48b3ccb8-0204-436f-9d40-2a057227964b
Hopper, John R.
df476df1-ddea-448b-bcaf-bf24f60d24ad
Van Avendonk, Harm J.A.
a8ed08ac-3232-480f-8760-bc7ee1edfbd0
Holbrook, W. Steven
639d0174-f356-4910-a394-c46a2ccb2919
Nunes, Gregory T.
23d0261a-dbcd-4bf4-b8b7-33a7b1bed314
Shillington, Donna J.
e53cb591-7124-4886-88a5-1b92f65fb199
Tucholke, Brian E.
284cd485-2bca-4494-829f-2fe592df96a8
Louden, Keith E.
b818fc43-6f0c-4cbd-99d1-3c60db40e9e8
Larsen, Hans Christian
48b3ccb8-0204-436f-9d40-2a057227964b
Hopper, John R.
df476df1-ddea-448b-bcaf-bf24f60d24ad

Van Avendonk, Harm J.A., Holbrook, W. Steven, Nunes, Gregory T., Shillington, Donna J., Tucholke, Brian E., Louden, Keith E., Larsen, Hans Christian and Hopper, John R. (2006) Seismic velocity structure of the rifted margin of the eastern Grand Banks of Newfoundland, Canada. Journal of Geophysical Research, 111 (B11), B11404. (doi:10.1029/2005JB004156).

Record type: Article

Abstract

We present a compressional seismic velocity profile of the crust of the eastern margin of the Grand Banks of Newfoundland, Canada. This velocity model was obtained by a tomographic inversion of wide-angle data recorded on a linear array of 24 ocean bottom seismometers (OBSs). At the landward side, we imaged a crustal thickness of 27 km in Flemish Pass and beneath Beothuk Knoll, which is thinner than the 35-km-thick crust of the central Grand Banks. We therefore assume that the eastern rim of the Grand Banks stretched uniformly by 25%. Farther seaward, the continental crust tapers rapidly beneath the continental slope to ?6 km thickness. In the distal margin we find a 60-km-wide zone with seismic velocities between 5.0 and 6.5 km s?1 that thins to the southeast from 6 to 2 km, which we interpret as highly extended continental crust. Contrary to other seismic studies of the margins of the Grand Banks, we find seismic velocities of 8 km s?1 and higher beneath this thin crustal layer in the continent-ocean transition. We conclude that mantle was locally emplaced at shallow levels without significant hydration from seawater or serpentinized mantle was removed along a décollement in the final stages of continental rifting. The outer edge of highly extended continental crust borders a 25-km-wide zone where seismic velocities increase gradually from 6.3 km s?1 just below the top of acoustic basement to 7.7 km s?1 at 5 km below basement. We interpret this area as a relatively narrow zone of exhumed and serpentinized continental mantle. Seaward, we imaged a thin and laterally heterogeneous layer with a seismic velocity that increases sharply from 5.0 km s?1 in basement ridges to 7.0 km s?1 at its base, overlying mantle velocities between 7.8 and 8.2 km s?1. We interpret this area as unroofed mantle and very thin oceanic crust that formed at an incipient, magma-starved, ultraslow spreading ridge. A comparison of the conjugate rifted margins of the eastern Grand Banks and the Iberia Abyssal Plain show that they exhibit a similar seaward progression from continental crust to mantle to oceanic crust. This indicates that before continental breakup, rifting exhumed progressively deeper sections of the continental lithosphere on both conjugate margins. A comparison between the continent-ocean transition of the Grand Banks and Flemish Cap shows that the final phase of continental rifting and the formation of the first oceanic crust required more time at the Grand Banks margin than at the southeastern margin of Flemish Cap.

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Published date: 2006
Keywords: continental rifting, marine geophysics, passive margin

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Local EPrints ID: 42192
URI: http://eprints.soton.ac.uk/id/eprint/42192
ISSN: 0148-0227
PURE UUID: 43fb0078-4349-46d9-913b-153f5ee9db57

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Date deposited: 22 Nov 2006
Last modified: 15 Mar 2024 08:46

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Contributors

Author: Harm J.A. Van Avendonk
Author: W. Steven Holbrook
Author: Gregory T. Nunes
Author: Donna J. Shillington
Author: Brian E. Tucholke
Author: Keith E. Louden
Author: Hans Christian Larsen
Author: John R. Hopper

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