The propagation of fold belts along curved convergent margins: Implications for the subandean fold-and-thrust belt.

摘要

Using analog models, we explore the role of lateral and vertical variations in crustal strength and deformation mechanism, due to changes in coupling and décollement rheology, on the development and distribution of topography and structures along a trenchward concave convergent margin in order to obtain insight into the development of the Subandean fold-and-thrust belt. We independently test the contribution of initial margin curvature and role of rheology, including single layer frictional and layered (friction over viscous) models. Kinematic and topographic analysis of our experiments indicate that initial margin curvature alone is not sufficient to focus deformation at the axis of the curvature when deformation is controlled by frictional mechanisms, even with a very large initial curvature. We find that a change in the rheology of overlying sedimentary rocks, from frictional to ductile, and strong coupling at the subduction zone interface can propagate horizontal shortening above a décollement and produce a distribution of topography and structural vergence similar to that seen in the Central Andes along the Eastern Bolivian Cordillera and Subandean fold-and-thrust belts. Furthermore, sharp lateral changes in the rheology of the overlying décollement, due to variations in the thickness and lithology of sedimentary basins, will greatly enhance the variation in style and distribution of this deformation along strike.