HR: 1330h
AN: T12A-0431    [PDF]
TI: Seismic Characterization Of Crust On The Newfoundland Non-Volcanic Rifted Margin: Prestack Depth Migrations Of The SCREECH Survey Around ODP Leg 210 Sites 1276 And 1277
AU: * Shillington, D J
EM: djs@uwyo.edu
AF: University of Wyoming, Department of Geology and Geophysics, P.O. Box 3006, Laramie, WY 82071 United States
AU: Holbrook, W S
EM: steveh@uwyo.edu
AF: University of Wyoming, Department of Geology and Geophysics, P.O. Box 3006, Laramie, WY 82071 United States
AU: Tucholke, B E
EM: btucholke@whoi.edu
AF: Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Clark 241, MS 22, Woods Hole, MA 02543 United States
AU: ODP Leg 210 Scientific Party, .
EM: Leg_210_Participants@odpemail.tamu.edu
AF: Ocean Drilling Program, Texas A and M University 1000 Discovery Dr., College Station, TX 77845 United States
AU: Hopper, J R
EM: jhopper@geomar.de
AF: GEOMAR, Marine Geodynamik, Wischhofstrassel 1-3, Kiel, D-24148 Germany
AU: Van Avendonk, H
EM: harm@ig.utexas.edu
AF: University of Texas Institute for Geophysics, 4412 Spicewood Springs, Austin, TX 76759 United States
AU: Louden, K
EM: Keith.Louden@Dal.Ca
AF: Dalhousie University, Department of Oceanography, 1355 Oxford St., Halifax, NS B3H 4J1 Canada
AU: Larsen, H C
EM: larsenhc@dlc.ku.dk
AF: Danish Lithosphere Centre, Oster Volgade 10, Copenhagen, DK 1350 Denmark
AB: The presence of 70 km of seismically featureless basement on the Newfoundland non-volcanic margin seaward of unambiguous continental crust and landward of recognized seafloor spreading anomalies has long fueled a debate concerning the affinity of crust within this ocean-continent transition zone. Proposed models include highly extended and intruded continental crust, slow-spreading oceanic crust, and serpentinized peridotite, each of which carries specific implications for margin formation and incipient seafloor spreading. One means of distinguishing between different crustal types is seismic reflection character. We present a grid of prestack depth migrated seismic reflection sections from the Newfoundland margin around recently drilled ODP Leg 210 Sites 1276 and 1277. Previously determined P-wave velocities and Poisson's Ratios calculated on SCREECH Transect 2 suggest the presence of over 75 km of oceanic crust on the Newfoundland margin that is not found on the conjugate Iberian margin. However, drilling at Site 1276, which lies in the transition zone, did not reach basement, so the affinity of this crust remains uncertain. Seismic and drilling investigations on the Iberian margin have revealed the presence of large tracts of exhumed, serpentinized peridotite between normal oceanic and normal continental crust. As a result, characterizing enigmatic crust on Newfoundland is essential for constraining the transition from late stage rifting to initial seafloor spreading. Drilling at Site 1276 recovered diabase sills an estimated 100-200 meters above basement. These sills typically have velocities of 5500-6000 m/s and are separated by lower velocity sediments, a small proportion of which have very slow seismic velocities and low densities (1600 m/s, 2.1 g/cc); initial shipboard work suggests that these sills might be the source of bright reflections that are found above transitional basement on SCREECH Transect 2. Large contrasts in density and velocity would be expected to generate a series of very large reflection coefficients in the lowermost sedimentary section and would likely impede signal penetration beneath the bright package of resulting reflections. Because these sills overlie a critical section of crust on the Newfoundland margin, understanding whether the featureless character results from signal penetration or properties of the crustal rocks themselves is critical to characterizing this unusual crust and thus placing constraints on the transition from amagmatic rifting to seafloor spreading.
DE: 3025 Marine seismics (0935)
DE: 8105 Continental margins and sedimentary basins
SC: Tectonophysics [T]
MN: 2003 Fall Meeting