HR: 1340h
AN: T23A-0524    [Abstracts]
TI: Dynamic Topography and the Density Structure of the Lithospheric Mantle
AU: * De Koker, N P
EM: dekoker@umich.edu
AF: Geological Sciences, University of Michigan, 2534 C.C. Little Building 1100 N. University Ave., Ann Arbor, MI 48109 United States
AU: Lithgow-Bertelloni, C
EM: crlb@umich.edu
AF: Geological Sciences, University of Michigan, 2534 C.C. Little Building 1100 N. University Ave., Ann Arbor, MI 48109 United States
AU: Stixrude, L
EM: stixrude@umich.edu
AF: Geological Sciences, University of Michigan, 2534 C.C. Little Building 1100 N. University Ave., Ann Arbor, MI 48109 United States
AB: Detailed isostatic studies of the Earth's surface require a comprehensive estimate of the density structure of the lithospheric mantle. We construct such a model estimate, and investigate its influence on resolving dynamic topography at the surface, in the context of limits in our current knowledge of the thermochemical structure of the lithospheric mantle. The only previous model of the lithospheric mantle structure, 3SMAC (Nataf & Ricard, 1996), assigned a pyrolitic composition to all subcrustal material, resulting in large negative dynamic topography in continental areas. Based on realistic estimates of the thermochemical structure of the lithospheric mantle, we construct a density model that accounts for variations in both the composition and depth extent of the chemically depleted layer, using a self consistent thermodynamic method. While the thermochemical structure is readily found from seafloor age in the oceans, accurate description of the more complex continental structure requires multiple parameters, each with its own range of uncertainty. The resulting uncertainty in the contribution of lithospheric density structure to the absolute magnitude of residual topography is comparable to the amplitude of dynamic topography predicted by mantle flow models. However, relative variations in residual topography over continents, may nonetheless be extracted and interpreted. These results show that 150-250 km thick roots of depleted material below cratons are required in order for cratons to lie above sealevel isostatically, giving support, fully independent of past and present seismological arguments, to the tectosphere concept first proposed by Jordan.
DE: 1219 Gravity anomalies and Earth structure (0920, 7205, 7240)
DE: 3010 Gravity and isostasy (1218, 1222)
DE: 7218 Lithosphere (1236)
DE: 8103 Continental cratons
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
SC: Tectonophysics [T]
MN: Fall Meeting 2005