HR: 0800h
AN: T41E-1273    [Abstracts]
TI: Distribution of Post-Rift Sills on the Newfoundland Nonvolcanic Margin Around the ODP Leg 210 Transect From Waveform Inversions and Synthetic Seismograms
AU: * Shillington, D J
EM: djshill@soc.soton.ac.uk
AF: Southampton Oceanography Centre School of Earth and Ocean Science, University of Southampton Empress Dock, Southampton, SO14 3ZH United Kingdom
AU: Holbrook, W S
EM: steveh@uwyo.edu
AF: University of Wyoming Department of Geology and Geophysics, 1000 E. University Ave. Dept. 3006, Laramie, WY 82071-3006 United States
AU: Karner, G D
EM: garry@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory Marine Geology and Geophysics, P.O Box 1000 61 Route 9W, Palisades, NY 10964-1000 United States
AU: Sawyer, D
EM: dale@rice.edu
AF: Rice University Department of Earth Science, 6100 Main Street MS 126, Houston, TX 77005 United States
AU: Deemer, S
EM: ecsoot@waves.esd.mun.ca
AF: Memorial University of Newfoundland Department of Earth Sciences, Room ER4063 Alexander Murray Bldg, St Johns, NL A1B 3X5 Canada
AU: Tucholke, B E
EM: btucholke@whoi.edu
AF: Woods Hole Oceanographic Institution Department of Geology and Geophysics, MS 22, Woods Hole, MA 02543 United States
AU: Shipboard Scientific Party, L
EM: www-odp.tamu.edu
AF: Ocean Drilling Program, Texas A&M University 1000 Discovery Drive, College Station, TX 77845-9547 United States
AB: Nonvolcanic rifted margins commonly include a section of crust of uncertain affinity between normal oceanic crust and extended continental crust. The origin of this portion of the margin, often called the transition zone, is essential to establishing the symmetry of rifted margins and developing models for margin evolution. The Newfoundland-Iberia rifted margin pair is among the best-studied nonvolcanic conjugate margin pairs in the world. Drilling on the Newfoundland nonvolcanic margin during ODP Leg 210 at Site 1276 did not reach enigmatic transitional basement, but did reveal the presence of interlayered sills and sediments immediately above the inferred top of transitional crust. The presence of sills has implications for the appearance of underlying transitional basement in seismic reflection sections, the signature of this section of the margin in shiptrack magnetic data and late-stage margin evolution. Sills are estimated to be approximately 100 m.y., while rifting likely occurred ~125 Ma. Shipboard work suggests that sills encountered at Site 1276 correspond to bright reflections in the lowermost sedimentary section overlying transitional crust that are observed in coincident seismic reflection profiles collected during the SCREECH (Studies of Continental Rifting and Extension on the Eastern Canadian SHelf) experiment during 2000. These profiles also show that basement in the transition zone is essentially featureless in seismic reflection data except where it rises above these bright reflections, implying either that impedance contrasts in the deep section prevent signal transmission or that there is little contrast between interlayered sills and sediments and the underlying basement. Here, we strengthen the link between seismic reflection data and drilling data by creating synthetic seismograms from physical properties measurements made at sea aboard ODP Leg 210. Physical properties data were used in lieu of logging data, which could not be collected due to poor hole conditions. To extend the results from Site 1276 to rest of the grid of seismic lines in this region, waveform inversions were also carried out on select supergathers around the SCREECH Line 2 survey and compared with waveform inversions of data near Site 1276. This work reveals significant variability in the velocity contrasts required by deep reflections thought to be associated with sills in the transition zone, implying similar variability in the distribution of sills. Furthermore, a distinct difference is observed between bright reflections overlying transitional crust and reflections at similar depths further seaward over unambiguous oceanic crust.
DE: 8102 Continental contractional orogenic belts
DE: 8109 Continental tectonics--extensional (0905)
DE: 0930 Oceanic structures
DE: 0935 Seismic methods (3025)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting