HR: 1330h
AN: T12A-0432    [PDF]
TI: Emplacement of the Peridotite Ridge Within the Ocean-Continent Transition on the West Iberia Continental Margin
AU: * Henning, A T
EM: ahenning@rice.edu
AF: Rice University, Department of Earth Science, MS - 126 6100 Main St., Houston, TX 77005 United States
AU: Sawyer, D S
EM: dale@rice.edu
AF: Rice University, Department of Earth Science, MS - 126 6100 Main St., Houston, TX 77005 United States
AB: The West Iberia continental margin began to form in the Late Triassic with the breakup of Pangea and culminated with the opening of the North Atlantic Ocean in the Early Cretaceous. While it is perhaps the best-studied continental margin in the world, the formation of a north-south segmented ridge of serpentinized peridotite located within the ocean-continent transition is not fully understood. The relatively thin sediment cover and lack of obvious volcanics make the Iberia margin an ideal place to study crustal features using seismic methods, and in 1997 the Iberia Seismic Experiment (ISE 97) collected over 4000 km of two-dimensional seismic reflection data off Iberia. Nine lines were recorded normal to the margin at a 10-25 km spacing and therefore provide cross-sections of the margin at regular intervals over a 200 km north-south distance. We prestack depth migrated the western portions of the nine margin-normal ISE 97 seismic lines. Interpretation of the depth sections suggests that the peridotite ridge is located within a broad zone of exhumed upper mantle that has been serpentinized. Total tectonic subsidence analyses provide minimum bounds on the thickness of the serpentinized layer, which extends from the zone of exhumed mantle landward under thinned continental crust. Exhumed upper mantle has previously been identified in the wider ocean-continent transition to the south in the southern Iberia Abyssal Plain, and we conclude that similar but narrower exposures occur to the north in the Galicia Bank area. While upper mantle appears to have been exhumed along all the ISE 97 lines, it does not always form a distinct basement ridge. Three ISE 97 profiles do not image a well-defined basement ridge, offering the first seismic evidence of a gap in the otherwise continuous peridotite ridge. Where it is well-developed, the peridotite ridge parallels a deeply-penetrating normal fault that developed near the end of rifting. This fault appears to penetrate into the upper mantle. We propose that this fault served as a conduit for water to localize serpentinization and cause the peridotite ridge to form diapirically within a broader zone of tectonically exhumed mantle.
DE: 3025 Marine seismics (0935)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8105 Continental margins and sedimentary basins
DE: 8109 Continental tectonics--extensional (0905)
DE: 9325 Atlantic Ocean
SC: Tectonophysics [T]
MN: 2003 Fall Meeting