Using nonlinear rheology in ASPECT: benchmarking and an application to subduction

ASPECT (Advanced Solver for Problems in Earth's ConvecTion) is a promising new code designed for modelling thermal convection in the mantle (Kronbichler et al. 2012). The massively parallel code uses state-of-the-art numerical methods, such as high performance solvers and adaptive mesh refinement. It builds on tried-and-well-tested libraries and works with plug-ins allowing easy extension to fine-tune it to the user's specific needs. It is a well-established fact that Earth's materials' behaviour is nonlinear and that for instance plastic yielding enables localization of deformation. This is of great importance for modelling lithosphere deformation processes, such as slab detachment (Andrews and Billen 2009). In light thereof, we have recently implemented a simple frictional plasticity criterion that can be combined with a viscous creep rheology, allowing for thermo-mechanically coupled visco-plastic flows. Three well-known benchmarks are used to test and validate our implementation of plasticity: the punch benchmark (Thieulot et al. 2008), which considers the indentation of a perfectly plastic material and allows for comparison with an analytical solution; the brick benchmark (Kaus 2010), performed in both a compressional and tensional regime with shear band angles bounded by results of other codes and theory; and the sandbox experiment by Buiter et al. (2006) modelling the time evolution of the extension of viscous and plastic layers in the presence of a free surface. We further showcase ASPECT's capabilities with a more geodynamical application including complex rheologies: the subduction of an oceanic plate in a three-dimensional thermo-mechanically coupled system. We show how the adaptive mesh refinement allows for very high resolution models while the code remains computationally efficient even in the presence of large deformation and large viscosity contrasts. Andrews, E. R. and Billen, M. I. (2009), Rheologic controls on the dynamics of slab detachment, Tectonophysics, 464, 60-69. Buiter, S. J. H. et al., 'The numerical sandbox: comparison of model results for a shortening and an extension experiment'. Analogue and Numerical Modelling of Crustal-Scale Processes, Buiter, S. J. H. and Schreurs, G. (eds). London: Geological Society, 2006. Kaus, B. J. (2010), Factors that control the angle of shear bands in geodynamic numerical models of brittle deformation, Tectonophysics, 484, 36-47. Kronbichler, M., Heister, T. and Bangerth, W. (2012), High Accuracy Mantle Convection Simulation through Modern Numerical Methods, Geophysical Journal International, 191, 12-29. Thieulot, C., Fullsack, P. and Braun, J. (2008), Adaptive octree-based finite element analysis of two-dimensional and three-dimensional indentation problems, Journal of Geophysical Research, 113.