HR: 10:50h
AN: T52B-03    [Abstracts]
TI: Depth-Dependent Extension at Passive Rifted Margins
AU: * van Wijk, J W
EM: jvanwijk@ucsd.edu
AF: IGPP, Scripps Institution of Oceanography, La Jolla, CA 92093-0225, La Jolla, CA 92093 United States
AU: Driscoll, N W
EM: ndriscoll@ucsd.edu
AF: IGPP, Scripps Institution of Oceanography, La Jolla, CA 92093-0225, La Jolla, CA 92093 United States
AB: Geophysical and well data from many conjugate rifted margins document the existence of large regional subsidence with only minor accompanying brittle deformation and erosional truncation. Both sides of these conjugate margins appear to be the "upper plate" in the simple shear model; this is called the "upper plate paradox" or "extra subsidence paradox". To explain the magnitude of the regional subsidence with little attendant brittle deformation requires significant lower crustal and/or mantle ductile extension across these margins, most dominant during the late stages of the rifting phase just prior to or during continental separation. This depth-dependent and temporally and spatially varying extension is observed at continental rift zones as well as at passive rifted margins, and may be a fundamental part of continental lithospheric extension. We use a numerical modeling approach to study the extra subsidence of the margin during the late-stage of continental rifting and the early-stage of seafloor spreading. The 2-D models of lithosphere deformation solve for visco-elastic plastic deformation and offer the ability to discern which mechanism accounts for the observed subsidence. Possible explanations for the late-stage subsidence that are tested include processes related to early seafloor spreading and corner flow, and late-stage depth-dependent extension caused by lower crustal flow that is either facilitated by warm upwelling asthenosphere during the final stages of rifting, or by asthenospheric temperature anomalies such as associated with mantle plumes. Preliminary results indicate that lithospheric thinning is time- and depth-dependent and spatially varying. The dominant deformation mode is found to change in time and to be influenced by the thermal structure of the lithosphere. There are many other factors that appear to affect lithosphere deformation during rifting such as thickness, composition, structure, and lateral variations in them.
DE: 8100 TECTONOPHYSICS
DE: 8109 Continental tectonics: extensional (0905)
SC: Tectonophysics [T]
MN: Fall Meeting 2005