Elle: the numerical simulation of metamorphic and deformation microstructures

We present a generalised framework for the numerical simulation of the evol ution of rock microstructures during deformation and metamorphism. This app roach is based upon a data structure that describes a polycrystalline mater ial using a two-dimensional network of nodes and connecting boundaries that allows micro-processes to be analysed at a range of scales. The nodes may possess attributes of position, topology and chemistry; and polygonal domai ns defined by these nodes may possess attributes of mineralogy, rheology an d lattice orientation. We represent the complex behaviour of deforming and metamorphosing rocks at the grain scale as the interaction of a set of loca lly-defined driving forces and micro-processes, calculated for small time s teps. A central program controls the evolution of extrinsic variables such as temperature and defines the history of deformation or metamorphic proces ses. The central program then passes the data structure to distinct process algorithms, which interact with this data structure, both by using it to d etermine the local values of driving forces, and by altering the attributes to simulate the progress of the process. We outline the function of the different aspects of the modelling task, pro vide simple examples showing porphyroblast growth during deformation and st atic grain growth, and describe the data structure that we have developed w hich enables us to handle multi-process simulations. (C) 2000 Elsevier Scie nce Ltd. All rights reserved.