HR: 17:05h
AN: T34A-05 INVITED     [Abstracts]
TI: Origin and evolution of lithospheric stresses in the Cenozoic
AU: * Lithgow-Bertelloni, C R
EM: crlb@umich.edu
AF: Department of Geological Sciences, University of Michigan, 425 E. University Avenue, Ann Arbor, MI 48109 United States
AB: The tectonic stress field is geophysically important because it is the agent that preserves in the crust a memory of dynamical processes. We use a finite element model of the lithosphere to calculate stresses induced by mantle flow, crustal heterogeneity and topography, in an attempt to elucidate the origin of the present-day state of stress. We compare all models qualitatively and quantitatively to observations of intraplate stresses as given by the World Stress Map. We explore the effects of varying assumptions for the mechanism of crustal compensation, for the viscosity structure of the mantle, and the effects of lateral variations in viscosity in the form of weak plate boundaries. We find that a combined model that includes both mantle and lithospheric sources of stress yields the best match to the observed present-day stress field (60% variance reduction) although there are many regions where agreement between observed and predicted stresses is poor. The stress field produced by mantle tractions alone shows a greater degree of long-wavelength structure than is apparent in the stress observations, but agrees very well with observations in some areas where radial mantle tractions (dynamic topography) are particularly strong such as in southeast Asia and the western Pacific. We observe strong spatial variability in the relative contributions of lithospheric and mantle sources of stress to the observed stress field. Hence, we conclude that lateral variations in the viscosity of the mantle, and in the rheology of the lithosphere leads to variable amounts of decoupling between lithosphere and mantle, allowing the mantle signature to dominate in some areas, and the crustal signature to dominate in others. We propose that comparison between predicted and observed stress fields may lead to constraints on the spatial variability of rheology in the lithosphere and mantle. We also examine the evolution of the stress field in the Cenozoic by considering the evolution of the mantle flow field in the last 64 my. Insofar as the variations in a mantle flow field dominated by subduction are small, we expect relatively small changes in the mantle contribution through time, except in areas of subduction initiation and cessation.
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8159 Rheology--crust and lithosphere
DE: 8164 Stresses--crust and lithosphere
DE: 8166 Stresses--deep-seated
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting