HR: 08:00h
AN: T31D-01 INVITED     [Abstracts]
TI: GyPSM-S: A synthesis model for fully-coupled geodynamic and petrological flow calculations related to subduction
AU: * Baker, L
EM: labaker@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 United States
AU: Smith, P
EM: psmith@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 United States
AU: Asimow, P
EM: asimow@gps.caltech.edu
AF: California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 United States
AU: Hall, C
EM: chall@gps.caltech.edu
AF: Seismological Laboratory, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 United States
AU: Gurnis, M
EM: gurnis@gps.caltech.edu
AF: Seismological Laboratory, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 United States
AB: A complete understanding of the subduction process requires a synthesis of issues typically emphasized by geochemists (phase relations, fluid migration, and melt properties) with those issues typically emphasized by geophysicists (development of the thermal regime, solid viscosity, buoyancy). Separate models exist that independently address these two approaches, but our goal is to fully couple these models into a self-consistent, adaptable system that allows for iterative feedback to occur between the dynamics and the chemistry. We present GyPSM-S, a model that combines the petrological model pHMELTS with a 2D thermal and variable viscosity flow model of a subduction zone. We are able to establish the thermal state and phase equilibria of the subducting oceanic slab and adjacent mantle wedge and constrain a fluid flux. This allows us to describe the process of hydration of the mantle wedge adjacent to the slab and define regions of melting. This is the first step leading to predictions of major element chemistry and evolution of arc volcanics, thus providing a critical connection between model and observation. We impose a Lagrangian particle distribution onto the finite-element mesh, with each particle representing one pHMELTS calculation per iteration. This translates into thousands of thermodynamic equilibrations; this densely sampled, continuously updating chemical dataset feeds back into the dynamics through viscosity, energy, and buoyancy terms. Using a parallel computing approach, we can iteratively solve for compositional fields consistent with a given thermal model, updating the viscosity field to reflect its dependence on water content in olivine. To this end, we apply improved olivine storage capacity measurements by Mosenfelder et al. (2005). Allowing the viscosity to be both compositionally and thermally dependent permits a consistent linkage between the effect of water addition to the mantle wedge and the wedge velocity field, leading to large-scale changes in the flow field of the hydrated wedge relative to the anhydrous case and predictions as to the fate of the hydrated material as subduction proceeds. Additionally, we take into account chemical feedback in the energy balance using a novel entropy transport formulation that implicitly accounts for latent heat effects as well as advection and diffusion. The flexibility of pHMELTS allows fractional melting to be included and provides realistic compositional and melt-related buoyancy terms. We address the extent and chemical variability of the melting region and how it responds to changes in potential temperature and slab velocity.
DE: 0545 Modeling (4255)
DE: 1009 Geochemical modeling (3610, 8410)
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
SC: Tectonophysics [T]
MN: Fall Meeting 2005