HR: 16:45h
AN: T44A-04    [Abstracts]
TI: Deformation of Oceanic Lithosphere Near Slow-spreading Ridge Discontinuities
AU: * van Wijk, J
EM: jvanwijk@ucsd.edu
AF: IGPP, Scripps Institute of Oceanography, La Jolla, CA 92093-0225 United States
AU: Blackman, D
EM: dblackman@ucsd.edu
AF: IGPP, Scripps Institute of Oceanography, La Jolla, CA 92093-0225 United States
AB: Transform and non-transform discontinuities that offset slow spreading mid-ocean ridges involve complex thermal and mechanical interactions. Effects of the truncated ridge are noticeable in the contrast between seafloor topography at inside corners and outside corners, along-axis variations in rift valley depth and crustal accretion, and distribution of earthquakes. At inside corners of ridge-discontinuity intersections, and along traces of discontinuities in older oceanic lithosphere, oceanic core complexes or mega-mullion structures are a rather common tectonic feature. In an attempt to understand deformation of oceanic lithosphere near ridge offsets, and conditions that may favor oceanic core complex formation, a three-dimensional thermo-mechanical model has been developed. The numerical approach allows for a more complete assessment of lithosphere deformation and associated stress fields in inside corners than was possible in previous 3-D models. The initial suite of results presented here focuses on deformation when axial properties do not vary along-strike or with time. This shows the extent to which plate boundary geometry alone can influence deformation. We find that non-transform discontinuities are represented by a wide, oblique deformation zone that tends to change orientation with time to become more parallel to the ridge segments. This contrasts with predicted deformation near transform discontinuities, where initial orientation is maintained in time. The boundary between the plates is found to be vertical in the center of the offset and curved at depth in the inside corners near the ridge-transform intersection. Ridge-normal tensile stresses concentrate in line with the ridge tip in the older plate opposite from the discontinuity and high amplitudes are absent in the inside corners during the magmatic accretionary phase simulated by our models.
DE: 8100 TECTONOPHYSICS
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8164 Stresses--crust and lithosphere
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting