Publication Date:
2022-05-25
Description:
Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 111 (2006): B11404, doi:10.1029/2005JB004156.
Description:
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
that thins to the southeast from 6 km 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 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 just below the top of acoustic
basement to 7.7 km/s at 5 km below basement. We interpret this area as a relatively narrow zone
of exhumed and serpentinized continental mantle. Seawards, we imaged a thin and laterally
heterogeneous layer with a seismic velocity that increases sharply from 5.0 km/s in basement
ridges to 7.0 km/s at its base, overlying mantle velocities between 7.8 and 8.2 km/s. We interpret
this area as unroofed mantle and very thin oceanic crust that formed at an incipient, magmastarved,
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.
Description:
The SCREECH program
was funded by the U.S. National Science Foundation grant OCE-9819053 to Woods Hole
Oceanographic Institution, by the Danish Research Foundation (Danmarks Grundforskningsfond),
and by the Natural Science and Engineering Council of Canada. HVA received support from the
University of Texas Institute for Geophysics and a Jackson School of Geosciences Fellow award.
BET acknowledges additional support from NSF grant OCE-0326714 and the Henry Bryant
Bigelow Chair in Oceanography at Woods Hole Oceanographic Institution.
Keywords:
Continental rifting
;
Marine geophysics
;
Passive margin
Repository Name:
Woods Hole Open Access Server
Type:
Article
Format:
application/pdf
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