Faults, Critical Taper, and the Mechanics of Foreland Basement-cored Uplifts

Bump, Alexander P.¹ (1) BP Exploration and Production Technology Group, Houston, TX

Foreland basement-cored uplift (FBCU) systems, such as the Laramide and Sierras Pampeanas, are the products of compressional deformation within continental interiors. They are composed of discrete, fault-bounded uplifts that are separated by low-lying, undeformed basins. They may be produced either by tectonic edge-load, as in continental collision, or by basal traction, as in flat-slab subduction. This paper presents a simple, two-dimensional analytical model for the mechanical evolution of these systems based on the explicit consideration of fault strength and the application of tectonic force. Fault strength is modeled as the sum of four components describing fault propagation, frictional and viscous drag on the fault plane, internal deformation of the hangingwall and gravity. Fault slip builds topography, increasing the weight of the hangingwall and effectively strengthening the fault. The model is based on the premise that faults build topography, gaining strength until they are in equilibrium with the applied tectonic force. The system of uplifts thus evolves toward a tapered envelope that is defined by the peaks of the high uplifts. The model offers predictions for gross topography, patterns of seismic activity and relative timing of uplift growth. The Sierras Pampeanas and central Asia are presented as examples.