HR: 10:35h
AN: T32A-02    [Abstracts]
TI: Comparison of Pure-Shear and Upwelling-Divergent Flow Models of Breakup Continental Lithosphere Thinning for the N. Iberian, N. Newfoundland and N. Angolan Rifted Margins
AU: * Kusznir, N J
EM: n.kusznir@liv.ac.uk
AF: Department of Earth and Ocean Sciences, University of Liverpool, Liverpool, L69 3BX, United Kingdom
AU: Manatschal, G
EM: manat@illite.u-strasbg.fr
AF: CGS-EOST, Universite Louis Pasteur, Strasbourg, F-67084, France
AU: Fletcher, R J
EM: rjf@liv.ac.uk
AF: Department of Earth and Ocean Sciences, University of Liverpool, Liverpool, L69 3BX, United Kingdom
AU: Cooper, C
EM: d22rsr@liv.ac.uk
AF: Department of Earth and Ocean Sciences, University of Liverpool, Liverpool, L69 3BX, United Kingdom
AB: Many rifted continental margins show a region > 200 km wide of highly thinned continental crust with thickness 10-15 km. Two different models of continental lithosphere thinning leading to continental breakup prior to sea- floor spreading initiation have been investigated and compared. One model assumes that continental lithosphere thinning is achieved by depth-uniform (pure-shear) lithosphere stretching. The second model assumes that continental lithosphere thinning is achieved by a combination of upwelling divergent flow within continental lithosphere and asthenosphere and pure-shear deformation. Both models have been applied to the N. Iberia - N. Newfoundland conjugate rifted margins and the N. Angolan rifted margin, and used to predict margin crustal thickness and lithosphere temperature. The isostatic response to crustal thinning, lithosphere geotherm perturbation and loading by observed sediment thickness have been determined. For both models the final breakup rupture of thinned continental lithosphere of thickness ~10-15 km is assumed to occur by normal faulting evolving into extensional detachments. Model predictions have been constrained using observed bathymetry and free air gravity anomaly. Both the pure-shear and upwelling divergent flow models of breakup lithosphere thinning are able to satisfactorily predict observed bathymetry and gravity anomaly. The best fit pure-shear model requires ~235 km of lithosphere extension for the N. Iberian - N. Newfoundland margin and 315 km for the N. Angolan margin. The best fit upwelling divergent flow model requires ~ 80 km of pure-shear extension for the N. Iberian - N. Newfoundland margin and ~25 km for the N. Angolan margin. Cross-plots of lithosphere and upper crustal thinning have been computed for both models. The upwelling-divergent flow model predicts depth- dependent lithosphere thinning and stretching which is particularly strong within the wide regions of highly thinned continental crust. Observations of depth-dependent stretching are compared with model predictions. For the N. Iberian - N. Newfoundland margins, the pure-shear breakup lithosphere thinning model predicts that the onset of melt generation occurs prior to breakup rupture of the continental crust for normal mantle temperature and chemical composition. In contrast the upwelling divergent flow model predicts the onset of melt generation after continental crust rupture leading to ~ 100 km mantle exhumation on each margin.
DE: 1219 Gravity anomalies and Earth structure (0920, 7205, 7240)
DE: 8105 Continental margins: divergent (1212, 8124)
DE: 8109 Continental tectonics: extensional (0905)
DE: 8159 Rheology: crust and lithosphere (8031)
DE: 8416 Mid-oceanic ridge processes (1032, 3614)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting