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 accompanied 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 comprise a more suitable interpretation for D′ and younger deformation. HIGHLIGHTS: 1) We study the early foreland deformation in the Fuegian Andes orogenic front. 2) Strain analysis of Upper Cretaceous rocks indicates deformation at upper-crustal depths. 3) Deformation was dominated by flexural folds and pressure-solution tectonic foliation. 4) Deformation progressed from layer-parallel shortening to folding and thrusting. 5) Successive non-coaxial strain orientations suggest a new tectonic model for the region.

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