|Title||The Time-Dependent Evolution of Subduction Zones : Interactions of the Lithosphere and Mantle|
|Project(s)||No Simula project|
|Publication Type||PhD Thesis|
|Year of Publication||2008|
|Degree awarding institution||Sydney|
|Publisher||University of Sydney|
|Place Published||University of Sydney|
This thesis addresses key issues in the time-evolution of subduction zones by carefully linking models with observations. Understanding the link between the lithosphere and the mantle has provided complex challenges because of the interdisciplinary nature of the subject. The process of subduction is one of the main ways that the mantle and lithosphere interact as the lithosphere is recycled into the mantle, slab-enriched mantle volcanics are emplaced on the surface and back-arc rifting on the overriding plate occurs. The down-going slab also pulls on the lithosphere as it sinks causing inundation of continents and the sediment loading of basins. This thesis creates a new methodology for understanding these processes, by combining plate-motion, age and subduction history with mantle convection models. This allows dynamic topography to be quantified both spatially and in time. The research shows that dynamic topography is within the constraints placed by external factors, such as the inundation of continents and anomalous subsidence reported in back-arc basins. The research also has implications for the density anomalies in the lower mantle that have often been used to predict dynamic topography - that a simple conversion between seismic velocity and mantle density does not work for the lower mantle. I have used the seismic tomography in the upper mantle to validate particular plate kinematic reconstructions for the Kamchatka and Tonga regions. This provides a new and important constraint on kinematic reconstructions which have often been more diagrammatic than rigorously defined by plate boundaries, in particular subduction trenches, which are self-consistent with the reconstruction of surface features and spreading ridges. Subduction models have also been used to explain the episodicity of compression, quiescence and extension on the overriding plate found in many of the world's back-arc basins. This episodicity is reproduced in three-dimensional subduction models by my innovative use of an overriding plate. The net force on the place, expressed as a surface velocity, is found to be the fundamental requirement in reproducing episodicity on the subducting plate. Periods of episodicity have been predicted according to the dynamic evolution of the subduction system.