Evaluating the Rheological Controls on Topography Development During Craton Formation: Objective Approaches to Evaluating Geodynamic Models

Cratons make up 60% of the world's continental lithosphere and are rich in resources, producing nearly all the world's diamonds and precious metals. They preserve the oldest known geology but there is no consensus regarding their formation nor how they became such long-lived lithospheric features. Our 2D numerical models (using the SOPALE code) examine rheological controls on lithosphere deformation and topography development during 50 Myr of compression aimed to simulate the lateral accretion phase of craton growth.

The initial model configuration has a 40 km thick laterally homogeneous crust overlying 110 km thick mantle lithosphere. A central 1200 km wide block of lithospheric material that is 3x stronger and 2 % less dense than the rest of the mantle lithosphere represents the depleted peridotite keel beneath cratons. Although the craton thickens slightly during the compression phase, most of the deformation occurs in the adjacent regions that have weaker lithosphere. Here the crustal thickness triples developing high topography in excess of 10 km without active erosion. These models test how changes to craton density, crustal strength, and other factors, influence the final geometry. For example, if the crust is stronger, it only doubles in thickness and more strain is accommodated by the cratonic block.

Each of the 46 parameters tested alters both the shape of the topography and lithosphere. A visual comparison of model outputs is tedious and subjective, risking misidentifying similarities and differences. We apply two quantitative analysis techniques to avoid human error when comparing models. The well-known signal analysis technique of cross-correlation effectively measures the degree of similarity between topography profiles. The Inter-related Distance of the Normalized Cross-Correlation (IDNCC) identified relative crustal strength as a key control on topography development. Principal component analysis (PCA) is better suited to holistically compare lithosphere deformation. With this method, specific characteristics of each model (lithosphere and crust thickness, heat flow, etc.) are incorporated to facilitate an overall comparison of lithosphere geometry. When used together, these two methods provide distinct and complementary information about the surface and subsurface deformation.