Microstructures and metamorphic reaction processes
The application of thermodynamic methods has revolutionised many areas of metamorphic petrology, such as the determination of pressures and temperatures of equilibration, and yet our understanding of the kinetics of metamorphic processes has lagged behind. For example, it is not known, in general, how far evolving metamorphic systems depart from chemical equilibrium, nor whether reactions proceed during brief episodes of rapid growth, or are slow, keeping pace with heat supply.
I developed an interest in these problems after working on the hornfelses associated with the Bushveld Complex in the 1980's, and developed a simple numerical model to study the interaction between nucleation and growth in metamorphic reactions and its implications for observable microstructure. In 1996 I began work again in this area with the help of graduate student Dan Lovegrove, who returned to the rocks in the field to constrain and test the modelling.
More recently, prompted by the common difficulty of reconciling the calculated equilibrium behaviour with the microstructural record in rocks, my focus has broadened to consider a wider range of processes responsible for the divergence between observation and calculation, including barriers to nucleation, sluggish dissolution of refractory phases, and evolution of the effective bulk composition by fractionation and other processes.
Here you will find (in reverse date order):
- 2010 - Equilibrium calculation and real metamorphic process: scenes from a troubled relationship. Invited lecture given at the Metamorphic Studies Group and at GeoCanada 2010, with case studies showing varied and informative departures from predicted equilibrium behaviour.
- 2003 - Microstructures of Reaction: materials relating to the first ISPET Seminar on Microstructural analysis of Metamorphic Rocks, Venice, October 2003.
- 2002 - Additional materials, including colour photomicrographs, to supplement Waters & Lovegrove (2002) Assessing the extent of disequilibrium and overstepping of prograde metamorphic reactions in metapelites from the Bushveld Complex aureole, South Africa, J. metamorphic Geol., 20, 135-149.
- 2002 - Long abstract of Dan Lovegrove's thesis.
- 1998 - Poster presentation (adapted from an open-day display) describing the background to the project.
- 1990 - A conference abstract from 1990 describing my earlier work.
Background reading on nucleation and growth kinetics
An introduction to some of the concepts:
Yardley, B.W.D. (1989) Introduction to Metamorphic Petrology, chapter 6, Metamorphic Textures and Processes. Longman. (You can omit those parts that relate to deformation)
Barker, A. J. (1998) Introduction to Metamorphic Textures and Microstructures, Chapter 5, Crystal Nucleation and Growth. 2nd Edition, Stanley Thornes (Publishers) Ltd.
Some more advanced reading:
- Carlson, W.D. (1989): The significance of intergranular diffusion to the mechanisms and kinetics of porphyroblast crystallization. Contributions to Mineralogy and Petrology, 103, 1-24.
- Carlson, W.D. (1991): Competitive diffusion-controlled growth of porphyroblasts. Mineralogical Magazine, 55, 317-330.
- Cashman, K.V., Ferry, J.M. (1988): Crystal size distribution (CSD) in rocks and the kinetics and dynamics of crystallization. III. Metamorphic crystallization. Contributions to Mineralogy and Petrology, 99, 401-415.
- Kerrick, D.M., Lasaga, A.C., Raeburn, S.P. (1991): Kinetics of heterogeneous reactions. In: Contact metamorphism, Kerrick, D.M., Ed., Mineralogical Society of America, Reviews in Mineralogy, 26, 583-671.
- Lasaga, A.C. (1986): Metamorphic reaction rate laws and development of isograds. Mineralogical Magazine, 50, 359-373.
- Ridley, J. (1986): Modelling of the relations between reaction enthalpy and the buffering of reaction progress in metamorphism. Mineralogical Magazine, 50, 375-384.
- Ridley, J., Thompson, A.B. (1986): The role of mineral kinetics in the development of metamorphic microtextures. In: Fluid-rock interactions during metamorphism (Advances in Physical Geochemistry, vol 5), Walther, J.V., Wood, B.J., Eds., New York, Springer-Verlag, 154-193.