Effect of a weak layer at the lithosphere-asthenosphere boundary on subduction dynamics

The aim of this thesis is to investigate and identify the first order effects of a weak layer at the lithosphere asthenosphere boundary (LAB) on a subduction zone, as to date, no previous geodynamics studies on this topic exist. The models developed are focussed on the study of a dynamically induced subduction through the use of 2-D and 3-D mechanical models involving a visco-plastic rheology. The results revealed that the process of an oceanic lithosphere subducting into the mantle can exhibit a wide range of behaviours depending on the weak layer characteristics such as its viscosity and density. Morphological and kinematic investigations of the time evolution of the model have allowed a correlation between the subduction plate velocity and the viscosity and density contrast between mantle and weak layer to be defined. Four possible subduction regimes were established, constraining the role of a weak layer for the parameters modelled. Therefore, the possible existence of a weak layer at the lithosphere asthenosphere boundary on subdution dynamics can affect subduction. From this study emerged an overall advancing trend for the plate with the resultant motion dependent on the constrained characteristics of the weak layer.