CONICET | Buscador de Institutos y Recursos Humanos

Abstract This contribution addresses new structural data from Upper Cretaceous-Danian sedimentary rocks of the Fuegian Andes orogenic front in Argentina. The structures studied, called D?, were formed during the early foreland deformation of the orogen, in the Late Cretaceous-Danian, in times when South America and Antarctica were still connected. The strain analysis of these structures indicates that deformation occurred at upper-crustal depths, and was characterized by flexural folding accompained by formation of pressure-solution tectonic foliations in zones of higher strain. Deformation intensities increase toward the hinterland and with depth. The history of deformation involved progression from layer-parallel shortening to folding above a detachment, and further formation of a forward propagating thrust wedge. Layer-parallel shortening and incipient folding recorded in Maastrichtian-Danian rocks indicate the leading edge of D? deformation. Non-coaxial finite strain orientations were involved during formation of D? structures along the Fuegian Andes front. These finite strain orientations cannot be explained with the SW-NE regional contraction usually assumed to have driven andean deformation in this region; alternatively, we consider that N-S contraction combined with buttressing against the cratonic foreland as a more suitable context for D? and younger deformation. Keywords: Strain analysis; Fuegian Andes; Upper Cretaceous-Danian; Upper-crustal deformation; Deformation history; non-coaxial strains; Butressing.