Constraining effective rheology through parallel joint geodynamic inversion

Abstract

The dynamics of crust and lithosphere is to a large extent controlled by its effective viscosity. Unfortunately, extrapolation of laboratory experiments indicates that viscosity is likely to vary over many orders of magnitude. Additional methods are thus required to constrain the effective viscosity of the present-day lithosphere using more direct geophysical observations.Here we discuss a method, which couples 3D geodynamic models with observations (surface velocities and gravity anomalies) and with a Bayesian inversion scheme on massively parallel high performance computers.We illustrate that the basic principle of a joint geodynamic and gravity inversion works well with a simple analytical example. In a next step, we test our approach using a synthetic 3D model of salt tectonics with erosion and sedimentation, and check how much noise conditions, model resolution, and sparse data coverage affect the resolving power of the method. Results show that it is possible to constrain the effective viscosity and density of layers that contribute to the large-scale dynamics, provided that those layers are numerically well resolved. The properties of thin layers that do not contribute much to the overall dynamics cannot be constrained, but noise or sparse data sampling does not significantly affect the inversion results.This thus illustrates that a joint geodynamic and gravity inversion is a potentially powerful method to constrain the dynamics of the crust and lithosphere. Having better constraints on the structure of the present-day crust and lithosphere will help to narrow the parameter space for models that aim to unravel lithosphere dynamics on a geological time scale.