Effect of basal friction on surface and volumetric strain in models of convergent settings measured by laser scanner

Abstract

This paper uses measurements by a high-accuracy laser scanner to investigate the role of basal friction on surface and volumetric strains in sandbox models simulating fold-thrust belts and accretionary wedges. We monitor progressive deformation, wedge growth, and strain distribution in three models with similar initial boundary conditions but with different basal frictions. Our analyses show that, in addition to influencing the kinematics and geometry of model wedges, basal friction also governs both the surface and volumetric strains of the wedge. After 16.3% bulk shortening, the volume decreased 5 ± 0.5%, 9.5 ± 0.5% and 12.5 ± 0.5% in the models shortened above low, intermediate and high friction decollements, respectively. Applied to nature, our model results suggest that more compaction and penetrative strain is expected in convergent settings with a high-friction decollement than those shortened above a low-friction decollement or a weak basal bed (like the salt formation under parts of the Zagros fold-thrust belt). This volume decrease probably reduces the porosity in the deformed lithologies.