Evidences of oblique rifting in the synrift deposits of the northern sector of the Neuquén Basin

Abstract

This study is focused on the Atueldepocentre, which sedimentary infill records the first stages of the NeuquénBasin opening during Late Triassic to Early Jurassic times in response toregional extensional processes. Our main goal was to determine the structuralcontrols related to the kinematics of the Atuel depocentre opening. We proposeas the main hypothesis that this sub-basin corresponded to an oblique rift. Inorder to confirm or discard this hypothesis, we integrated the kinematicanalysis of small-scale fault-slip data with timing and orientation of the mainnormal faults. The general orientation of the Atuel depocentre was controlledby two NNW oriented main structures, the Alumbre and La Manga normal faults, interpreted as possibly reactivated Paleozoic structures. On the otherhand, the internal structure of the depocentre is characterized by a bimodalpattern of WNW and NNW oriented faults. The kinematic data from small-scalefaults show a NE extension direction (mean λ = Az 046°) oblique to the main NNW rifttrend, supporting the hypothesis that the Atuel depocentre evolved as anoblique rift. We estimated a regional extension direction oriented NNE, withpossible refraction to a NE extension inside the rifted area, with respect tothe regional motion. The main factor that controlled the development of anoblique rift was a strong strain localization in the reactivated Alumbre and La Manga faults. This localization would had been responsible for several distinctive characteristicsthat mark the difference between the Atuel and other depocentres of thenorthern sector of the Neuquén basin.