HR: 1330h
AN: V12C-0610    [PDF]
TI: Melt Evolution Beneath Mid-Ocean Ridges and Mantle Plumes From a Coupled Thermodynamic and Geodynamic Model
AU: * Tirone, M
EM: tironem@fiu.edu
AF: CeSMEC, Florida International University University Park Campus, Bldg. VH150, Miami, FL 33199 United States
AB: We have developed a model that combines a Gibbs free energy minimization routine incorporating the thermodynamic database for melts, pMELTS (Ghiorso et al., G3, 2002) and a geodynamic multiflow 2D numerical model that solves transport equations for mass, heat, momentum and chemical elements. The effects of latent heat, viscous dissipation and adiabatic heating are also included in the model. For brevity only few common features for melting in mid-ocean ridges and plumes are discussed here. Local equilibrium approximation is the main assumption of the model (Knapp, GCA, 1989). From experimental data on diffusion in mantle minerals, the approximation seems reasonable if porous flow is assumed as the mechanism of melt transport within the molten region. Channeling flow, induced by dissolution reactions (melting) (Spiegelman et al., JGR, 2001), is observed through large portions of the mantle. The location of the channels is extremely variable in time and size. Channels are defined here as mantle regions where melt fraction is approximately 2-3 times higher than the surrounding mantle and where melt transport is still controlled by porous flow. Melt far from the plume/ridge axis accumulates at the base of the lithosphere (Sparks and Parmentier, EPSL, 1991) and the residence time in this area determines periodic fluctuations in the melt extraction to the surface. In the plume model, reactivation of the melting process is observed at about 350 km from the plume axis. Petrology and geochemistry of residual solids and melt are the result of a polybaric process with continuos melt mixing. Preliminary comparison with data from lavas, melt inclusions, abyssal peridotites and mantle nodules shows that the model, within the limits of the available thermodynamic database, produces petrological and major elements geochemical variability similar to that observed in natural samples.
DE: 3035 Midocean ridge processes
DE: 3655 Major element composition
DE: 3939 Physical thermodynamics
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8434 Magma migration
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting