Subsidence Mechanisms of Sedimentary Basins Developed over Accretionary Crust

Abstract

This thesis uses forward modelling to investigate the formation of intercratonic basins upon accretionary crust. It began from the hypothesis that accretionary crust forms with a near normal thickness crust, but a thin lithosphere inherited from the terranes that compose it. After the accretion process has ceased the lithosphere stabilises and begins to cool, causing it to grow thicker and this in turn drives subsidence of the accretionary crust. A 1-D finite difference computer code was developed to model conductive heat flow through a column of cooling lithosphere and asthenosphere. To test the hypothesis, the subsidence produced by the modelling of this process was compared to the observed subsidence from backstripping numerous basins situated on accretionary crust
The model produced a good fit to the subsidence in a detailed case study of two of the Palaeozoic basins in North Africa. The study was then extended to test the applicability of to accretionary crust globally. It found that while using measured values of the crust and lithospheric thickness for each region the model produced subsidence curves that matched the observed subsidence in each basin. It makes a more coherent argument for the formation of these basins that is able to explain a wider variety of features than other proposed subsidence mechanisms such as slow stretching or dynamic topography. These results suggest that such subsidence is an inherent property of accretionary crust which could influence the evolution of the continental crust over long time periods.
The model was used to investigate the subsidence of the West Siberian Basin and found the subsidence patterns to be consistent with the decay of a plume head which thinned the lithosphere. This subsidence patterns indicate the plume material thinned the lithosphere over an area of 2.5 million km2 resulting in uplift before it cooled and subsided.