HR: 09:30h
AN: T41A-04    [Abstracts]
TI: Predicting Structure and Location of the Ocean-Continent Transition at Rifted Margins Using a New Model of Continental Breakup and Rifted Margin Formation
AU: * Kusznir, N J
EM: n.kusznir@liverpool.ac.uk
AF: Department of Earth and Ocean Sciences, University of Liverpool, Liverpool, L69 3BX United Kingdom
AU: Karner, G D
EM: garry@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964 United States
AU: Tymms, V
EM: vtymms@liverpool.ac.uk
AF: Department of Earth and Ocean Sciences, University of Liverpool, Liverpool, L69 3BX United Kingdom
AU: Healy, D
EM: dhealy@liverpool.ac.uk
AF: Department of Earth and Ocean Sciences, University of Liverpool, Liverpool, L69 3BX United Kingdom
AU: Roberts, A M
EM: alan@badleys.co.uk
AF: Badleys Geoscience, Hundleby, Spilsby, PE23 5NB United Kingdom
AB: The structure and width of the ocean-continent transition (OCT) at rifted continental margins shows great diversity for both non-volcanic and volcanic margins. Some non-volcanic margins show broad regions of exhumed mantle within the OCT while others show broad regions of very thin upper continental crust above mantle. While many volcanic margins show a sharper OCT, others show broad regions of continental crustal thinning. Both non-volcanic and volcanic rifted continental margins, including conjugate margin pairs, show depth-dependent lithosphere stretching in which stretching of the lower continental crust and lithosphere greatly exceeds that of the upper crust. Determining the structure and location of the OCT at rifted continental margins and the processes responsible for its formation represent key goals of rifted continental margin research and challenges to deep-water hydrocarbon exploration at rifted margins. Depth-uniform stretching is not the dominant deformation process for thinning continental lithosphere leading to breakup; it cannot explain observed depth-dependent lithosphere stretching. A new model of continental lithosphere thinning leading to breakup and sea-floor spreading initiation has been developed which assumes that thinning occurs in response to an upwelling divergent flow field within continental lithosphere and asthenosphere. Model formulation uses corner-flow predicted by kinematic iso-viscous stream-function or finite element solutions to advect continental lithosphere and asthenosphere material and their temperature fields. Flow is defined by Vx, the divergence half-velocity, and Vz, the vertical upwelling velocity. The new model predicts depth-dependent lithosphere stretching prior to sea-floor spreading initiation for both non-volcanic and volcanic margins, and mantle exhumation at non-volcanic margins. Thinning of continental margin crust and lithosphere temperature evolution are sensitive to the velocity ratio Vz/Vx. For Vz/Vx of the order of 1, corresponding to plate boundary driven divergence, the model predicts exhumation of continental lithospheric mantle and a broad OCT with lateral dimension up to 100 km as observed at non-volcanic margins. For large initial values of Vz/Vx, corresponding to buoyancy assisted flow at volcanic margins, the predicted OCT is sharper with little or no exhumation of continental lithospheric mantle. The rate of upward propagation of the upwelling divergent flow field through continental lithosphere during breakup deformation initiation has a strong control on margin structure, OCT width, and the extent of mantle exhumation. Crustal thinning and lithosphere temperature predicted by the new margin formation model are used to determine rifted margin bathymetry and gravity anomalies. Observed bathymetry and gravity anomalies have been used to invert for breakup deformation kinematic parameters which may be used to predict margin structure, OCT location, and subsidence and heat-flow history. The new margin formation model has been successfully applied to the Goban Spur, Grand Banks, and Iberian non-volcanic margins, and the Lofoten and Voering volcanic margins using observed bathymetry, gravity and sediment thickness data to invert for the kinematic parameters describing lithosphere breakup deformation. The preferred models of these margins require only small components of pre-breakup depth-uniform lithosphere stretching. This work forms part of the NERC Margins iSIMM project.
DE: 8105 Continental margins and sedimentary basins
DE: 8109 Continental tectonics--extensional (0905)
DE: 8110 Continental tectonics--general (0905)
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8122 Dynamics, gravity and tectonics
SC: Tectonophysics [T]
MN: 2005 Joint Assembly