HR: 0800h
AN: T41A-0369    [Abstracts]
TI: Characterization of the U reflection on the Newfoundland Margin: Evidence for Wide-Spread Early Postrift Magmatism on ‘Magma-Poor' Rifted Margin
AU: * Peron-Pinvidic, G
EM: gwenn.peron-pinvidic@eost.u-strasbg.fr
AF: EOST-CGS, 1 rue Blessig, Strasbourg, 67084, France
AU: Shillington, D
EM: djshill@noc.soton.ac.uk
AF: NOC, European Way, Southampton, SO14 3ZH, United Kingdom
AU: Tucholke, B
EM: btucholke@whoi.edu
AF: WHOI, Woods Hole, Woods Hole, MA 02543-1, United States
AB: Drilling during ODP Leg 210 on the magma-poor Newfoundland margin revealed evidence for varying amounts of both syn- and early post-rift magmatism. Here, we focus on post-rift magmatism that appears to have affected the deep margin ~10-15 m.y. after the onset of seafloor spreading. Two postrift sills (105.3 and 97.8 Ma) were encountered in the deep sediments overlying ‘transitional' basement at Site 1276. These sills have been linked to bright reflections in seismic reflection data by means of synthetic seismograms. The shallower of the two sills is at least locally coincident with the U reflection which is observed throughout the Newfoundland Basin and which has been interpreted by some authors to mark final breakup of continental lithosphere. However, the lateral extent of the sills in the Newfoundland Basin and their relation to the U reflection away from Site 1276 has been uncertain. Likewise, the cause of the magmatism and the relationship between the sills and other contemporaneous magmatic features is unknown. Our study investigates the magnitude and nature of the post-rift magmatic event by mapping the U reflection and associated bright reflections throughout the deep Newfoundland margin. U is characterized by relatively high amplitudes and good continuity. It is generally flat and limited to the zone landward of magnetic anomaly M3, pinching out on basement both continent-ward and northward. The reflection is often underlain by reflections with comparable or higher amplitudes that are interpreted to represent sills. Disruptions are often observed in the sub-U stratigraphic sequence, and these may represent pathways of magma injection. To complement the seismic facies mapping we have also created a series of synthetic seismograms to explore variations in sill properties that might account for observed variations in seismic reflection characteristics. Our results indicate that the level of the U reflection was the preferred depth at which sills were intruded (at least for initial injection), possibly because it was a level of hydrostatic equilibrium and/or a stratigraphic level of weakness. The widespread distribution of high-amplitude reflections associated with sill-like geometries implies that sills are ubiquitous throughout the Newfoundland Basin. The restriction of major post-rift magmatism to the Newfoundland margin may indicate that it was associated with passage over the Madeira and Canary hotspots, which affected the Iberia plate only at its southern margin and only beginning at c.70 Ma.
DE: 3036 Ocean drilling
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8105 Continental margins: divergent (1212, 8124)
DE: 8109 Continental tectonics: extensional (0905)
DE: 8178 Tectonics and magmatism
SC: Tectonophysics [T]
MN: 2007 Fall Meeting