Cratons Through the Ages

Increased seismic imaging has provided more detailed views of the Earth's lithosphere, and with it, new insight into the varied shapes of cratons. If considered to be permanent, long-lived features within the Earth's interior, then why are there variations in observed craton shapes? Are the variations due to recent deformation or can multiple shapes be long-lived over the Earth's history? Prior work has shown that relative buoyancy and viscosity of this ancient lithosphere and the relationship with its underlying mantle directly affect the survivability of craton shapes. Other work demonstrated that shape itself can impact overall craton stability with some shapes more resistant to deformation than others. However, the impact of variance in convective vigor (as represented by the mantle Rayleigh number) on craton shape has yet to be thoroughly studied. As the mantle's internal temperature, and correspondingly mantle Rayleigh number, decreases with time, its viscosity and convective vigor increases. These changes may impact which shapes may be stable and long-lived. In other words, differing mantle conditions (or Rayleigh number) may favor stability for differing craton shapes. Understanding this potential could constrain which shapes may last longer in changing mantle conditions without significant deformation whereas other shapes may evolve through either regional or large-scale deformation. This increased knowledge on the control on craton shape is important. A craton's shape can indicate properties we cannot directly observe from the surface, such as rheology of composition of the lithosphere. In addition, knowing and understanding the stability of a craton shape can better inform interpretations of present-day shapes and whether they are evidence of past or present deformation, or formation. Here, we will present results from numerical modeling that tests various mantle conditions against craton shape, rheology, and composition, to determine the impact of mantle Rayleigh number on the shape of cratons.