Evidencias de extensión oblicua en los depósitos de sinrift del sector norte de la Cuenca Neuquina

This study is focused on the Atuel depocentre, which sedimentary infill records the first stages of the Neuquén Basin opening during Late Triassic to Early Jurassic times in response to regional extensional processes. Our main goal was to determine the structural controls related to the kinematics of the Atuel depocentre opening. We propose as the main hypothesis that this sub-basin corresponded to an oblique rift. In order to confirm or discard this hypothesis, we integrated the kinematic analysis of small-scale fault-slip data with timing and orientation of the main normal faults. The general orientation of the Atuel depocentre was controlled by two NNW oriented main structures, the Alumbre and La Manga normal faults, interpreted as possibly reactivated Paleozoic structures. On the other hand, the internal structure of the depocentre is characterized by a bimodal pattern of WNW and NNW oriented faults. The kinematic data from small-scale faults show a NE extension direction (mean λ1 = Az 046°) oblique to the main NNW rift trend, supporting the hypothesis that the Atuel depocentre evolved as an oblique rift. We estimated a regional extension direction oriented NNE, with possible refraction to a NE extension inside the rifted area, with respect to the regional motion. The main factor that controlled the development of an oblique rift was a strong strain localization in the reactivated Alumbre and La Manga faults. This localization would had been responsible for several distinctive characteristics that mark the difference between the Atuel and other depocentres of the northern sector of the Neuquén basin.