ADVANCES IN MODELING CONTACT METAMORPHISM: 3D THERMAL AND FLOW STRUCTURES, MINERAL TEXTURAL ANALYSES AND INTERPRETIVE VISUALIZATION

The success of the RiM&G series derives, in part, from the breadth of topics embraced by the term "mineralogy". Not only are the final products, minerals, to be covered, but also the most up-to-date knowledge concerning the processes that lead to their development and subsequent modification. The 1991 Contact Metamorphism volume brought together the products and processes involved in thermal metamorphism and highlighted directions for further study. Since that time, our ability to computationally model these complex systems has greatly matured. Computational domains increased to 3-D and 4-D (with time), and more realistic algorithms were incorporated for fluid production, latent heat of crystallization, dehydration reactions, permeability evolution and other phenomena. Commensurate with these advances is the ability to visualize large datasets in 3-D, animate and interpret their dynamic evolution over time. All of this leads to a more thorough understanding of the spatial and temporal evolution of field variables, particularily temperature. P-T-t paths derived from these complex calculations provide the input for kinetic models of mineral growth and textural development in contact aureoles, thus allowing us to directly evaluate the impact of thermal evolution and its controlling factors on mineral textures.

As a specific example of advancement, recent work incorporates non-linear fluid production from the magma into models of aureole development. Models with a 3km thick sill, initially at 875^oC emplaced at 12km depth, suggest that with ≤ 5% fluid produced from the melt, maximum temperatures increase only a few degrees over the same systems lacking magmatic fluid. Most fluid production occurs early in the thermal history (< 250,000 yrs) as the melt crystallizes, although temperatures remain higher near the contact for up to 500,000 yrs when compared to systems without magmatic fluid production. For these systems (Rayleigh number ≈ 200) fluid production has a minimal impact on large scale flow dynamics, in contrast to previous suggestions. As parameters having a significant influence on contact aureole development are analyzed, mineral textures responding to these perturbations are constructed. This allows identification of the linkage between thermal evolution of the aureole and its preservation in the rock record.