HR: 0800h
AN: T11C-0721    [Abstracts]
TI: Numerical Models of Lithosphere-Mantle Interaction at Continental Rift Zones
AU: van Hunen, J
EM: jeroen.van-hunen@durham.ac.uk
AF: Department of Earth Sciences, Durham University, Science Labs, Durham, DH1 3LE, United Kingdom
AU: * van Wijk, J
EM: jolante@lanl.gov
AF: Los Alamos National Laboratory, MS D443, Los Alamos, NM 87545, United States
AB: Extension of continental lithosphere results in thinning of both the crust and mantle lithosphere. As a result of the thinning, mantle material wells up beneath the rift zone. Replacement of the colder lithosphere material with warmer mantle material may result in a thermal anomaly beneath the rift zone that is possibly visible in tomographic images. Tomographic images of the upper mantle below the Rio Grande rift indeed show a low seismic wave velocity anomaly extending to about 100-180 km depth. They also indicate that small-scale convection occurs in the rift zone, and that colder (or high seismic wave velocity-) material appears to be present at both sides of the rift. Numerical models of mantle flow beneath a continental rift predict small scale convection in the rift zone. Material flows upward under the center of the rift and downward at its sides, resulting in small temperature variations. The mantle material that fills the rift zone is supplied from the asthenosphere and flows from both sides into the rift zone. Extending the lithosphere to the point of breakup shows that the upwelling velocity increases toward the end of the continental rift phase (late syn-rift). After continental break up, the upwelling decreases and a mid-ocean ridge system is formed. The varying upwelling pattern during the different phases has implications for magmatism during rifting; it predicts for example that most melt is formed at the late-syn-rift stage.
DE: 8100 TECTONOPHYSICS
DE: 8105 Continental margins: divergent (1212, 8124)
DE: 8109 Continental tectonics: extensional (0905)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting