HR: 14:25h
AN: V53F-04    [Abstracts]
TI: Chemical Evolution of Dynamic Mantle Models with Strong, Mobile Lithosphere.
AU: * Brandenburg, J
EM: jpbrande@umich.edu
AF: University of Michigan, Dept. of Geological Sciences, 2534 C.C. Little Building, 425 East University, Ann Arbor, MI 48109-1063 United States
AU: van Keken, P
EM: keken@umich.edu
AF: University of Michigan, Dept. of Geological Sciences, 2534 C.C. Little Building, 425 East University, Ann Arbor, MI 48109-1063 United States
AU: Ballentine, C
EM: chris.ballentine@man.ac.uk
AF: University of Manchester, M13, Manchester, 9PL United Kingdom
AU: Hauri, E
EM: hauri@dtm.ciw.edu
AF: 3Carnegie Institution of Washington, Dept. of Terrestrial Magnetism, 5241 Broad Branch Road, NW, Washington, DC 20015 United States
AB: In recent years, a number of models that examine the chemical evolution of the mantle have been put forth by the geodynamics community. Important criteria such as heat flow and degassing rate are reconciled by these models, but the full range of isotopic heterogeneity as observed in oceanic basalts is not reproduced. The inherent numerical difficulty of representing extreme variations in mantle viscosity while maintaining a mobile, segmented lithosphere may be reflected in this problem. Thick, stagnant lithosphere is the inevitable consequence of realistic temperature dependent rheology. Special numerical techniques are needed to break the lithosphere into plates. However, some choices for tuning parameters are inherent in all such methods. The variability of modeled isotopic heterogeneity as a function of the numerical treatment of the lithosphere is explored. Mantle convection is simulated by the numerical solution of the time dependent Boussinesq equations on a two dimensional finite element mesh. Two related techniques for maintaining a mobile lithosphere, the kinematic plate and force balance method, are used. In the kinematic plate method (Christensen and Hofmann, 1994) an arbitrary plate velocity field is applied to the surface boundary. The force balance method (Gable, 1989) is functionally the same, except that the plate velocities are computed to minimize the shear stress on the base of the lithosphere. Isotopic inventories are discretized to a large number of passive tracers. Mixing properties and isotopic evolution of the Rb/Sr, U/Pb, Sm/Nd, U/He, and K/Ar systems are compared. A solidus model for peridotite melting is then introduced. Given these features, we examine the sensitivity of the geochemical evolution to the different methods of modeling the lithosphere.
DE: 0545 Modeling (4255)
DE: 1009 Geochemical modeling (3610, 8410)
DE: 1030 Geochemical cycles (0330)
DE: 8121 Dynamics: convection currents, and mantle plumes
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005