Seismic velocity structure of the rifted margin of the eastern Grand Banks of Newfoundland, Canada
Van Avendonk, Harm J. A.
Holbrook, W. Steven
Nunes, Gregory T.
Shillington, Donna J.
Tucholke, Brian E.
Louden, Keith E.
Larsen, Hans Christian
Hopper, John R.
MetadataShow full item record
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.
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.
Suggested CitationJournal of Geophysical Research 111 (2006): B11404
Showing items related by title, author, creator and subject.
Organic matter in river-influenced continental margin sediments : the land-ocean and climate linkage at the Late Quaternary Congo fan (ODP Site 1075) Holtvoeth, Jens; Wagner, Thomas; Schubert, Carsten J. (American Geophysical Union, 2003-12-31)Late Quaternary sections (1.2 Ma) of ODP-Site 1075 from the Congo deep-sea fan are investigated to reconstruct variations of terrigenous organic matter supply to the eastern equatorial Atlantic. To characterize the organic ...
An evaluation of 14C age relationships between co-occurring foraminifera, alkenones, and total organic carbon in continental margin sediments Mollenhauer, Gesine; Kienast, Markus; Lamy, Frank; Meggers, Helge; Schneider, Ralph R.; Hayes, John M.; Eglinton, Timothy I. (American Geophysical Union, 2005-01-25)Radiocarbon age relationships between co-occurring planktic foraminifera, alkenones and total organic carbon in sediments from the continental margins of Southern Chile, Northwest Africa and the South China Sea were ...
Modeling sulfate reduction in methane hydrate-bearing continental margin sediments : does a sulfate-methane transition require anaerobic oxidation of methane? Malinverno, Alberto; Pohlman, John W. (American Geophysical Union, 2011-07-12)The sulfate-methane transition (SMT), a biogeochemical zone where sulfate and methane are metabolized, is commonly observed at shallow depths (1–30 mbsf) in methane-bearing marine sediments. Two processes consume sulfate ...