HR: 0800h
AN: T41E-1272    [Abstracts]
TI: A Kinematic Fluid-flow Model of Continental Lithosphere Deformation Leading to Continental Lithosphere Breakup and Rifted Continental 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
AB: The observations of depth dependent lithosphere stretching at rifted continental margins and the exhumation of continental lithosphere mantle at non-volcanic margins are not explained by depth-uniform lithosphere stretching. Depth dependent lithosphere stretching, in which stretching of the continental lower crust and lithospheric mantle greatly exceeds that of the upper crust or upper crustal extension is entirely absent, is observed at both volcanic and non-volcanic margins. The dominant process for thinning rifted continental margin lithosphere is not depth-uniform intra-continental extension. A kinematic fluid-flow model of continental lithosphere deformation leading to continental lithosphere breakup and sea-floor spreading initiation has been developed in which a divergent upwelling flow field is applied to continental lithosphere and asthenosphere. The model uses a iso-viscous stream-function corner-flow to predict the flow field which is used 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 distribution of thinning of the continental margin crust and lithospheric mantle and the evolution of the lithosphere and asthenosphere temperature field are particularly sensitive to the velocity ratio Vz/Vx. The model predicts depth dependent stretching of rifted continental margin lithosphere for both volcanic and non-volcanic margins, as observed. For non-volcanic margins (where Vz/Vx ~1) the model predicts exhumation of continental lithospheric mantle and a diffuse ocean-continent boundary with lateral dimension ~ 100 km. For volcanic margins (where initially Vz/Vx > 5 due to buoyancy assisted flow) the predicted ocean-continent transition is sharper and little or no exhumation of continental lithospheric mantle is predicted. The model predicts that most depth dependent stretching of continental margin lithosphere occurs before continental lithosphere rupture and the onset of sea-floor spreading. Predicted crustal thinning and lithosphere temperature may be used to predict the development of margin bathymetry, subsidence history, top basement heat-flow and gravity anomaly. The model has been successfully applied to volcanic and non-volcanic margin examples using observed bathymetry, gravity and sediment thickness data to invert for the kinematic parameters describing lithosphere breakup deformation. During the initiation of the divergent upwelling flow field within continental lithosphere and asthenosphere, the model predicts subsidence of the lithosphere surface above the developing flow-field with amplitude ~ 2km and width ~ 100-200 km, but with no associated stretching of the upper crust. Such behaviour is consistent with the observation of regional subsidence in the absence of upper crustal stretching as observed at the propagating tip of sea-floor spreading in the Woodlark and South China Sea Basins.
DE: 8105 Continental margins and sedimentary basins
DE: 8109 Continental tectonics--extensional (0905)
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8122 Dynamics, gravity and tectonics
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting