HR: 1340h
AN: V23B-0631    [Abstracts]
TI: Poisson's Ratio Structure Through a Zone of Exhumed Mantle at the Goban Spur Rifted Margin, Southwest of the UK.
AU: * Bullock, A D
EM: ab397@soc.soton.ac.uk
AF: Southampton Oceanography Centre, University of Southampton European Way, Southampton, SO14 3ZH United Kingdom
AU: Minshull, T A
EM: tmin@soc.soton.ac.uk
AF: Southampton Oceanography Centre, University of Southampton European Way, Southampton, SO14 3ZH United Kingdom
AB: Zones of exhumed mantle have been identified at the west Iberia and Goban Spur rifted margins in the eastern North Atlantic where they form a transition zone up to 130 km wide between thinned continental crust and oceanic crust further seaward. P-wave velocities range from $\sim$4~km~s$^{-1}$ at top basement to 7.2-7.6~km~s$^{-1}$ at 4-6~km depth into basement and taken in isolation are consistent with a wide range of contrasting lithologies. Poisson's ratio may be used as a discriminator between possible compositions as, for P-wave velocities $<$6~km~s$^{-1}$, serpentinite can be clearly distinguised from basalt. We present here the Poisson's ratio structure through the zone of exhumed mantle at the Goban Spur margin up to 4~km into basement. Velocities are constrained by seven ocean-bottom hydrophones and six sonobuoys across this region at a separation of $\sim$15~km; S-wave arrivals are observed on five ocean-bottom hydrophones in this region as P-to-S conversions occurring at top basement. A regularised inversion with smoothing constraints was used to define the P- and S-wave velocity structures individually and the Poisson's ratio computed from these models.
DE: 8180 Tomography
DE: 8105 Continental margins and sedimentary basins
DE: 3025 Marine seismics (0935)
DE: 3035 Midocean ridge processes
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting