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Geometry, kinematics and strain magnitudes in the internal Fuegian fold-thrust belt, north of Lago Fagnano, Tierra del Fuego, Argentina.

Abstract

At the southernmost tip of the Andes the internal domain of the Fuegian thin-skinned fold-thrust belt encloses the geometric and kinematic connection with the inner orogenic belt located to the south and the external fold-thrust belt to the north. This collisional mountain belt developed during closure of the Rocas Verdes marginal basin, where marine transgression had led to deposition of organic rich shales. During the Late Cretaceous, forelandward tectonic loading gave rise to the Austral foreland basin, which nowadays holds important hydrocarbon reserves. As a result of tectonic loading and overpressure, a detachment formed in source rocks cropping out in the study area. Since this detachment links deformation with the internal belt, its study is essential to develop a tectonic model for the region, including the behavior of potential source rocks of the Austral Basin. It´s been proposed that the detachment is the roof thrust of a duplex formed in the hinterland. Relaying on intensive field survey of the cretaceous rocks above the detachment, this research attempts to provide insights into the tectonic mechanisms that yield to propagation of deformation from the hinterland toward the foreland. Geometry of thrust faults and their relationship with folds, lineations and foliations will be analyzed. Strain markers will allow to improve balanced cross-sections where penetrative deformation had led to volume-loss. This quantitative and qualitative research will allow establishing constraints on timing and amount of shortening in key zones of the orogenic belt that host rocks of economic interest, which remain poorly known to date.