EXPERIMENTAL SIMULATION OF EROSION AND ITS CONTROL ON THE KINEMATICS AND GEOMETRY OF A FOLD-AND-THRUST BELTS

Field studies and models indicate that erosion exerts a primary control on the evolution of orogenic wedges. When erosion redistributes mass across Earth's surface, the near-surface lithostatic stresses are modified, producing changes in the state of stress that alter critical wedge geometries, which in turn affects the growth and internal deformation of orogenic wedges. Somewhat arbitrary and simplistic rules are often used to simulate erosion in sandbox models, and the geometric evolution of such models has not been quantitatively compared with that expected from theory and/or numerical simulations. In this study, we use analogue experiments and numerical simulations (using the GALE modeling package) of a deforming sand wedge to investigate the effect of systematically varying erosion intensity (K) on the geometry and kinematics of experimental fold-and-thrust belts modeled in the sandbox. Our approach is novel in that we use an erosion rule that removes mass from the scaled sand wedge according to rates expected from fluvial bedrock incision. The geometry of the models is quantitatively compared with that expected from theory. The fold-and-thrust belt growth rate is inversely proportional to K and is well predicted by theory, except when erosion is vigorous—in this case, the wedge grows supercritically. As erosional intensity increases, the number of fore-shear bands decreases, while the shear strain along each increases. The results indicate that realistic and mechanistic erosion rules can be effectively applied to experimental simulations to model mass removal. This approach holds the possibility of calibrating strain history to erosion intensities for predictions in natural settings.