Descripción: Triassic clastic and volcanic rocks from the Precordillera were deposited in the Cuyana rift basin filling half-graben systems. Contractional/transpressional Andean tectonics leads to the almost complete inversion of some portions of the basin which resulted in present-day isolated, structurally controlled outcrops of these Triassic rocks. In the Southern Precordillera both the degree of Neogene tectonic inversion and structural compexities are variable. At the regional scale, these variations in Andean deformation are related to first order anisotropies like the Cuyana basin borders and previous shear zones of Permian age (San Rafael orogenic phase). This paper focuses on the kinematic analysis done in the Cerro Manantial thrust sheet area (Cordón San Bartolo, central sector of the South Precordillera) where tectonic inversion was not that strong and the influence of oblique strain zones is practically null. Four sets of extensional/ transtensional faults were recognized affecting Triassic sedimentary rocks of the El Cielo Formation (Uspallata Group) at the Quebrada El Salto. Fault displacements are of decimetric to metric scale. Mesoscopic kinematic indicators (en-échèlon tensional gashes, Riedel shear fractures, sigmoidal fractures) were measured. Once Andean deformation was restored, a NNE direction for the Triassic extension was determined. Considering a northern branch of the Cuyana basin trending NNW (Az. 150°) and oblique to the direction of extension (Az. 35-40°), a sinistral strike-slip component could be inferred for this portion of the basin.

Descripción: The Gondwana margin contained some Triassic basins that together constitute a regionally northwest-trending extensional system. The Cuyana rift Basin is internally composed of a family of hemigrabens filled with thick piles of sedimentary clastic and epiclastic rocks that can reach more than three thousand meters. In particular the Rincón Blanco sub-basin, one of the northernmost depocenter of this rift, is bounded by a linked through-going normal fault that usually displays an en-échèlon map view. Along strike existence of discrete depocenters and alternation of sedimentary wedges of different types suggest a linkage origin for some of them separated by a transfer zone. The infilling was strongly controlled by tectonics which in term produced distinctive features along the whole sedimentary sequence. An immediate consequence of this latter is that the architecture of the fill resulted from the geometry and the displacement of the bounding normal faults. Using lithology and structural data the infilling was subdivided into packages of genetically linked units bounded by regional extended surfaces. Hence, three depositional sequences or tectono- stratigraphic units separated by regional unconformities have been recognized. They were interpreted as a result of a major reactivation of the extensional system that could have evolved along strike as segments of fault that linked together and/or as laterally propagating faults. Using these basic concepts it was possible to reconstruct the geometry and the history of the infilling of the east margin of the hemigraben, buried under several backthrusts. Additionally, it could be possible to separate a sequence of rock, the Marachemill Unit, from the Rincón Blanco Group and to understand their tectonosedimentary relationships.