A Kinetic Model for Crystallization in the Hydrous Haplogranite System (Ab-Or-Qtz-H2O)

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9814524LondonIn the high-silica melts that represent granitic systems in moderate- to low-PT regimes, growth kinetics of quartz and alkali feldspars are important to the overall minimization of free energy and hence to attainment of chemical equilibrium during crystallization. The central goal of this work is to develop a comprehensive model for the coupled nucleation and growth kinetics of crystalline phases from undercooled hydrous melts of haplogranite composition (system Ab-Or-Qtz-H2O). The project possesses two essential parts: a set of experiments needed to provide the basic data on nucleation and crystal growth in undercooled granitic systems, and a numerical model by which to relate the experimental phenomena to the thermodynamic, kinetic, and transport properties of the crystal-melt system. Key measurements sought from experiments will include: (1) time of structural relaxation in melt, (2) nucleation delay, (3) rate of change of crystal size distribution, (4) mineral modes and compositions, (5) onset of diffusion-controlled growth, and (6) the creation and dispersion of boundary layers in melt. These data will be summarized in the form of rate laws, such as those we have developed for the system Ab-Qtz-H2O using the solution modules of Wolfram Research Software MATHEMATICA. The final goal of the program is to develop kinetic models that can accurately predict the crystallization response in undercooled granitic melts.