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Research Results

  • A Molecular Dynamics Study of the Glass Transition in CaAl2Si2O8: Thermodynamics and Tracer Diffusion
  • A Molecular Dynamics Approach to the Computer Glass Transition of CaAl2Si2O8
  • Geochemical Evolution of Magma Bodies
  • High Temperature & Pressure Corner and Edge Sharing in Anorthite

Research Summary

Fluid Dynamic Simulations of Magma Transport Phenomena This includes various studies of the transport of mass, momentum, heat, and chemical species in magmatic systems at the macroscopic scale, of vital importance to an understanding of the evolution of magmatic, hydrothermal and sedimentary basin systems. This work involves a number of sub-projects including study of the properties of sodium aluminosilicate melts by laboratory and numerical experiment, investigation of the dynamics of magma origin, ascent, and withdrawal, and study of the dynamics of thermohaline porous media convection. Utilizing a sophisticated computer code that faithfully captures details of convection in two-component melts undergoing phase change, the work includes:

  1. Up-grading code to 3-dimensions with some technical improvements including more realistic two-phase non-Newtonian rheology,
  2. Expansion of code capability to multicomponent natural systems using best thermodynamic database available,
  3. Analysis of the 'crustal anatexis driven by basaltic underplating' paradigm,
  4. Study of the behavior of silicate mush piles, specifically the spontaneous development of melt channels within the mush during cumulate formation
  5. Modeling of radial-zonation of Sierran-type granitic plutons.

Additionally, magma withdrawal calculations enable one to forward model the removal of magma at high rates of discharge through conduit systems connected to density- and viscosity-stratified magma bodies within the crust. Extensive results have been obtained and are published in the Journal of Geophysical Research. Non-Newtonian magma properties have a demonstrable effect on magma withdrawal. Finally, time-dependent simulations of thermohaline convection in fractured (equivalent) porous media show that, at fixed porosity and thermal Rayleigh number, as the salinity Rayleigh number (Rs) increases the dynamics change from convective steady-state at low Rs to chaotic flows at higher Rs and finally to conductive steady state at the highest Rs. The eulerian chaos observed may be relevant to the interpretation of fluid inclusions in that fluid salinities at a fixed location may vary chaotically in time. Molecular Dynamics Simulations of Melt Structure and Properties: A collaboration between myself and Spera yielded laboratory results indicating that all melts in the system NaAlSiO4 - SiO2 are examples of strong fluids characterized by Arrhenian activation energies for viscous flow which are independent of temperature but which depend on composition: (Ea (silica) = 515 kJ/mol; Ea (nepheline) = 320 kJ/mol). Molecular Dynamics Simulations indicate that many thermodynamic and transport properties may be adequately predicted using pairwise-additive effective pair potentials. Activation energy for oxygen self diffusion in nepheline melt is circa 150 kJ/mol at 3GPa and 2500 kelvins. Ionic conductivity of NaAlSiO4 melt is about 100 mho/m with an activation energy of 65 kJ/mol. This is similar to the MD and laboratory value of 58 kJ/mol for sodium self-diffusivity. Experimental Rheology of Silicate Melts and Magmatic Mixtures: This program investigates the non-Newtonian flow properties of molten silicates and multiphase mixtures at high temperatures using techniques of rotational viscometry. Currently under development is a new instrument which will allow us to extend considerably the ranges of temperature (1000 - 1600 C) and deformation rate of these studies.

University of California, Santa Barbara

Department of Earth Science