Discrete element modelling of rift-basin evolution
mediaposted on 07.06.2021, 12:54 by Emma Finch
Evolution of a single phase rift basin in three-dimensions using a discrete element model. The crust is represented as a two-layered brittle-ductile system where faults nucleate, propagate and interact in response to local heterogeneities and resulting stresses. Interactions between element pairs in the upper crust are defined as brittle where bonds break to form faults. Those in the lower crust are firmoviscous where there is displacement on elements to represent faults but no bonds are broken. Gravity and isostacy terms are included allowing the medium to be buoyant around a pre-defined depth resulting in flexure of the crust.
The model dimension is initially 60 x 60 x 30 km, with the upper 15 km representing the brittle crust. The movie shows the rift extending at intervals of 200 kyr towards the viewer to a maximum time of 6 Myr (30% extension). At the maximum displacement, selected faults are marked and the location of these faults with depth is then shown as the model is sliced in intervals of 4 horizons. The slicing goes through the brittle crust and into the ductile lower crust, stopping at horizon 30, where flexure of the ductile layer relative to the overlying faults can be seen.
The white to dark brown colouring shows increasing distance of an element from its initial neighbours as a proxy for displacement on faults. The darkest coloured elements represent the greatest throw on a fault and a collection of white elements demonstrate faults blocks. The elements within these blocks are still in contact with the majority of their initial neighbours but are being tilted within the hangingwalls and footwalls of neighbouring faults to form grabens, tilted half-grabens and horst blocks. Dark brown colours (>2 km throw) highlight maximum displacement at the centre of a fault which reduces down to pale yellow (~50 m throw) at fault tips.
If you want further information on the methodology and results from this work, please take a look at the associated peer-reviewed publication, Finch and Gawthorpe, 2017.