Crustal structure across the Grand Banks–Newfoundland Basin Continental Margin – II. Results from a seismic reflection profile |
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| Authors: | K W Helen Lau Keith E Louden Sharon Deemer Jeremy Hall John R Hopper Brian E Tucholke W Steven Holbrook Hans Christian Larsen † |
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| Institution: | Department of Oceanography, Dalhousie University, Halifax, Nova Scotia B3H 4J1,;Canada. E-mail: Department of Earth Sciences, Memorial University of Newfoundland, St. John's, Newfoundland A1B 3X5,;Canada Danish Lithosphere Center, Øster Voldgade 10, DK-1350;Copenhagen K, Denmark Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543,;USA Department of Geology and Geophysics, University of Wyoming, Laramie, WY 82071,;USA |
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| Abstract: | New multichannel seismic reflection data were collected over a 565 km transect covering the non-volcanic rifted margin of the central eastern Grand Banks and the Newfoundland Basin in the northwestern Atlantic. Three major crustal zones are interpreted from west to east over the seaward 350 km of the profile: (1) continental crust; (2) transitional basement and (3) oceanic crust. Continental crust thins over a wide zone (∼160 km) by forming a large rift basin (Carson Basin) and seaward fault block, together with a series of smaller fault blocks eastwards beneath the Salar and Newfoundland basins. Analysis of selected previous reflection profiles (Lithoprobe 85-4, 85-2 and Conrad NB-1) indicates that prominent landward-dipping reflections observed under the continental slope are a regional phenomenon. They define the landward edge of a deep serpentinized mantle layer, which underlies both extended continental crust and transitional basement. The 80-km-wide transitional basement is defined landwards by a basement high that may consist of serpentinized peridotite and seawards by a pair of basement highs of unknown crustal origin. Flat and unreflective transitional basement most likely is exhumed, serpentinized mantle, although our results do not exclude the possibility of anomalously thinned oceanic crust. A Moho reflection below interpreted oceanic crust is first observed landwards of magnetic anomaly M4, 230 km from the shelf break. Extrapolation of ages from chron M0 to the edge of interpreted oceanic crust suggests that the onset of seafloor spreading was ∼138 Ma (Valanginian) in the south (southern Newfoundland Basin) to ∼125 Ma (Barremian–Aptian boundary) in the north (Flemish Cap), comparable to those proposed for the conjugate margins. |
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| Keywords: | continental margins crustal structures reflection seismology rifted margins seismic structures |
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