FANTOM: Two- and three-dimensional numerical modelling of creeping flows for the solution of geological problems

A new finite element code for the solution of the Stokes and heat transport equations is presented. It has purposely been designed to address geological flow problems in two and three dimensions at crustal and lithospheric scales. A variety of rheologies has been implemented including nonlinear thermally activated creep and brittle (or plastic) frictional models. A cloud of particles is used to track materials in the simulation domain which allows to record the integrated history of deformation; its density is variable and dynamically adapted. The code is built on the Arbitrary Lagrangian-Eulerian kinematical description: the computational grid deforms vertically and allows for a true free surface while the computational domain remains of constant width in the horizontal direction. The code can be run in sequential or parallel mode. The parallelisation is based on the MPI paradigm and the domain decomposition algorithm is presented. The solution to the large system of algebraic equations resulting from the finite element discretisation and linearisation of the set of coupled partial differential equations to be solved is obtained by means of an efficient (sequential or massively parallel) direct solver. Details of implementation concerning plasticity, cloud handing, nonlinear convergence, strain accumulation and pressure smoothing are given. The sequential 2D version of the code is used to run the numerical sandbox benchmark at normal and high resolutions. The 2D parallel version is used in the case of a thermo-mechanically coupled extension experiment in which the mantle is present. The 3D parallel version is used to run a crustal scale orogeny experiment. The overall performance of the code, as well as the respect of the incompressibility constraint, of the yield stress criterion and of the volume conservation are discussed, along with parallel scalability. Benchmark results of scalar field advection, the Rayleigh-Taylor experiment and the falling block experiment are presented in Appendix. (C) 2011 Elsevier B.V. All rights reserved.