Structural evolution of The Collón Cura basin: Tectonic implications for the north Patagonian Broken Foreland

Abstract

The distribution and timing of the deformation for the North Patagonian broken foreland is nowadays suggested by expansion and retraction of the orogenic activity during the middle to late Miocene Andean contractional phase. Dissimilar interpretations with diachronic tectonic schemes were proposed. Based on a new U-Pb (LA-MC-ICP-MS) zircon age of 10.6 ± 0.2 Ma and a structural analysis improved with soft sediment deformation evidences interpreted as seismites, the structural evolution and deformational events of one of the main Neogene depocenters from the North Patagonian foreland (i.e. Collón Cura basin) was developed. The structural evolution of the Collón Cura basin took place through three deformational stages during a lapse of ∼11 Myr. This involves the main structural configuration of the basin at the early-middle Miocene (∼16 Ma – 14.4 Ma), which follows up to middle Miocene (10.6 Ma), and minor evidences of deformation to the late Miocene (Pre-4.8 Ma). During the first deformational stage (∼16 Ma - 14.4 Ma), the west and east main margin fault systems of the basin were active. This stage involved the uplifting of the North Patagonian Andes and the Sañicó Massif. The deformation proceeds in the western fault system synchronously to the inactivation of the eastern fault system during the second deformational stage (14.4 Ma - 10.6 Ma). The third deformational stage (Pre-4.8 Ma) only occurred at the interior of the basin as results of in-sequence and out of sequence progression of the deformation from the main margins of the basin towards the interior of it. This stage occurred without changes in the basin configurations. The results obtained in this work indicate that the main structural configuration of the Patagonian Broken Foreland occurred since the beginning of the early-middle Miocene Andean contractional episode. In turn, the structural evolution suggests that the deformation occurred synchronously in the North Patagonian Andes as well as in the North Patagonian foreland region.