A contribution to the quantification of crustal shortening and kinematics of deformation across the Western Andes ( ? 20–22° S)

Abstract. The Andes are an emblematic active Cordilleran orogen. Mountain building in the Central (?20? S) started by Late Cretaceous to early Cenozoic along subduction margin and propagated eastward. In general, structures sustaining uplift of western flank dismissed, their contribution mountain remains poorly constrained. Here, we focus on two sites Western at ?20–22? S Atacama desert, where well exposed. We combine mapping from high-resolution satellite images with field observations numerical trishear forward modeling provide quantitative constraints kinematic evolution investigated sites. When upscaling our local interpretations regional scale, identify main structures: (1) Andean Basement Thrust, a west-vergent thrust system placing Paleozoic basement over Mesozoic strata, (2) series thrusts pertaining West Thrust System, deforming primarily units. From interpreted sections, estimate that both together accommodate least ?6–9 km shortening across sole ?7–17 wide This multi-kilometric represents only fraction total accommodated whole Andes. timing deformation recorded folded can be bracketed between ?68 ?29 Ma – possibly ?44 dated deformed geological layers, subsequent significant slowing-down rates. Even though forming absorbed small orogen, was relatively earliest stages before proceeded