HR: 13:40h
AN: T33D-01 INVITED    [Abstracts]
TI: Predictions From Numerical Models of Continental Extension Using Ductile Failure.
AU: * Lavier, L L
EM: luc@ig.utexas.edu
AF: Institute for Geophysics, Jackson School of Geosciences, UNiversity of Texas at Austin, J.J. Pickle Research Campus, Bldg. 196 10100 Burnet Road (R2200), Austin, TX 78758-4445, United States
AU: Manatschal, G
EM: manatschal@illite.u-strasbg.fr
AF: Universite Louis Pasteur, CGS_EOST,Universite Louis Pasteur 1, rue Blessig, Strasbourg, 67084, France
AU: van Avendonk, H J
EM: harm@ig.utexas.edu
AF: Institute for Geophysics, Jackson School of Geosciences, UNiversity of Texas at Austin, J.J. Pickle Research Campus, Bldg. 196 10100 Burnet Road (R2200), Austin, TX 78758-4445, United States
AB: We present numerical experiments of lithospheric extension using a parameterization for ductile failure in both the brittle and ductile media. We use a ductile fracture criterion based on Freudenthal's critical plastic work done per unit volume. This allows us to model the formation of a semi-brittle media in the continental crust. To be consistent with geological observations ductile fracture is limited to the temperature range corresponding to the onset of quartz and plagioclase plasticity (300?C to 450?C) and the strength of the crust is decrease from that of plagioclase to that of quartz. This approach allowed us to model the evolution of rifted margins and to predict the occurrence of characteristic structures observed at continental margins. These include the presence of a continental block (block H) hanging between seaward dipping normal faults, the observation of exhumed continental crust and mantle along detachment faults working as rolling hinges and the possible influence of a gabbroic lower crust on the evolution of the margin. For initial and boundary conditions similar to that of magma poor margins, we were able to model three consecutive phases of deformations that are consistent with geological and geophysical observations in the Alps, Iberia and Newfoundland. (1) A stretching phase during which deformation is distributed over the whole future subsiding margin and extension is rooted in a semi-brittle layer. (2) A thinning phase when extension is controlled by a system of superimposed concave-downward faults active simultaneously in the brittle upper crust and lower crust/upper mantle (3) An exhumation phase during which serpentinized mantle rocks are exhumed to the seafloor along a downward-concave path and which eventually led to continental break-up and seafloor spreading. We show that by only varying the initial geotherm in the lithosphere we are able to isolate 3 different characteristic styles of extension. An initially hot stretching style which first develops core complexes structures followed by half-grabens similar to those observed in the Basin & Range Province. An initially cold thinning style which leads to the formation of a narrow rift with large rift flank uplift and structures similar to the Rio Grande rift.
DE: 1847 Modeling
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8100 TECTONOPHYSICS
DE: 8105 Continental margins: divergent (1212, 8124)
DE: 8122 Dynamics: gravity and tectonics
SC: Tectonophysics [T]
MN: 2007 Fall Meeting