Paleozoic-early Mesozoic structural evolution of the West Gondwana accretionary margin in southern Patagonia, Argentina

Abstract

The Upper Devonian-Upper Triassic low-grade metasedimentary rocks exposed along the South Patagonian Andes preserve the structural record of deformation associated with pre-Andean orogenic phases that predated the inception of the Jurassic rift during Gondwana fragmentation. Through the structural analysis at different scales, we identified deformation structures mainly with cratonward vergence, produced at two stages of structure development for the Bahía de la Lancha (early Carboniferous) and Río Lácteo (Middle Devonian-early Carboniferous) formations, and in a single one, for the Nunatak Viedma Unit (Late Triassic). The structural features were integrated with available U–Pb detrital zircon ages and fission-track cooling ages from those units. It leads us to identify a westward younging of sedimentation (i.e. protolith deposition) and widening of the continental margin throughout Paleozoic-early Mesozoic times, tectonically stabilized during the late Carboniferous-middle Permian Gondwanide orogeny and the Late Triassic-Early Jurassic Chonide orogeny. The structural style holds features of fold-and-thrust belts, which is discussed in a context of accretionary tectonics inherent to the Terra Australis exterior orogen.