HR: 0800h
AN: T11E-1334    [Abstracts]
TI: On the Survival of a Heterogeneous Deep Mantle Reservoir: Constraints from Evolutionary Numerical Mantle Convection Models
AU: * van Summeren, J R
EM: summeren@geo.uu.nl
AF: Utrecht University, P.O. Box 80.021, Utrecht, 3508 TA Netherlands
AU: van den Berg, A P
EM: berg@geo.uu.nl
AF: Utrecht University, P.O. Box 80.021, Utrecht, 3508 TA Netherlands
AU: van der Hilst, R D
EM: hilst@mit.edu
AF: Massachusetts Institute of Technology (MIT), 77 Massachusetts Avenue, Cambridge, MA 01239 United States
AB: The concept of a compositional heterogenous reservoir, in the deep lower mantle, has become increasingly popular in recent years, due to indications from seismology, geochemistry and heat budget calculations. In this study, the dynamic feasibility of this concept was investigated, using numerical modeling techniques. We applied 2-D cartesian and cylindrical geometry and a time window of 4.5 Gyr in our thermo-chemical mantle convection models. The models include the effects of the endothermic phase transition at 660 km depth in the extended Boussinesq approximation. We use finite elements for the solution of the convection equations. Composition dependence of several physical parameters is represented by Lagrangian tracer particles in a particle-in-cell implementation. We studied the dynamic evolution of a compositionally distinct layer at the bottom 20 percent of the mantle volume, with a positive density contrast in the order of 1% and time dependent internal heating, increased with respect to the background mantle. The results show a clearly bounded stability domain in a domain-diagram with density contrast and internal heating rate. Preliminary results suggest that the layer stability is smaller for models with cylindrical geometry due to the different surface/volume ratios for the deep lower mantle. We also show that the parameters of the endothermic phase transition have a large impact on the evolution of the compositional layering. Vigorous mantle convection, once it sets in, controlled by the phase transition, produces cold downwellings which eventually destroy the layering with (sub)critical density contrasts.
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 8125 Evolution of the Earth
DE: 1025 Composition of the mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting