HR: 0800h
AN: T21B-0595    [Abstracts]
TI: Uncertainty in the Relationship Between Lithospheric Structure and the Surface Stress Field
AU: * Naliboff, J
EM: johnbn@umich.edu
AF: Department of Geological Sciences, University of Michigan, 2534 C. C. Little Building, 1100 North University Ave, Ann Arbor, MI 48109-1005, United States
AU: Lithgow-Bertelloni, C
EM: crlb@umich.edu
AF: Department of Earth Sciences, University College London, Gower Street, London, WC1E 6BT, United Kingdom
AB: Variations in lithospheric thickness and density contribute to the Earth's surface stress field. The relationship between the continental lithosphere's isostatic state, sub-crustal structure and the surface stress field, however, remains unresolved due to the poor constraints on its thickness, composition and rheology. Here, we present calculations that systematically explore variations in the surface stress field as a function of isostatic compensation mechanism, dynamic vs. observed elevations, sub-crustal continental lithosphere structure and assumed "coupling depth". We compute the gravitational potential energy (GPE) of 2x2 degree lithospheric columns and then solve for the resulting stress field in a 3D elastic finite element model. Consistent with previous calculations, the stress regime and orientation varies significantly between continental lithospheric structures with compensated vs. uncompensated crustal layers. Imposing Pratt vs. Airy compensation, however, has comparatively minor effects on the overall stress orientations and regimes. Subtracting dynamic topography calculated from a mantle flow model results in additional large variations in stress orientation and regime in areas with large values of positive or negative dynamic topography. Varying the thickness of the continental mantle lithosphere as a function of crustal thickness or tectonic province does not produce significantly different results than models where the thickness is set by the difference between the crustal and compensation depths. To test the relationship between the surface stress field and decoupling between brittle and ductile portions of the lithosphere, we decrease the depth to which the GPE is calculated. We find that the stress field varies strongly as the global GPE integration depth decreases, which suggests that stresses may change significantly as the rheology of the lithosphere varies both vertically and horizontally. Finally, we address a number of assumptions inherent in the GPE method that oversimplify or fail to address rheological and structural complexities in the continental lithosphere, which may strongly influence the surface stress field.
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8122 Dynamics: gravity and tectonics
DE: 8159 Rheology: crust and lithosphere (8031)
DE: 8164 Stresses: crust and lithosphere
DE: 8168 Stresses: general
SC: Tectonophysics [T]
MN: 2007 Fall Meeting