Abstract We present a study of the brittle tectonics of Tunas Alkaline Complex focusing on the kinematic and geometric analysis of faults and brittle shear zones deforming the complex. The data acquired and respective interpretations sought to contribute to the post-Cretaceous tectonic structural models of southern Brazil. The ~83 Ma-old alkaline complex is made up of syenites, alkali syenites, plutonic and volcanic breccias, as well as trachyte, microsyenite, and bostonite dykes. Morphostructural analysis using remote sensing combined with right dihedral kinematic analysis of fault-slip data and relations of intersections among structures allowed us to characterize four Cenozoic paleostress fields and their respective tectonic pulses: (I) Eocene-Oligocene NW-SE extension responsible for normal oblique-slip faults striking N60-70E; (II) Oligocene-Miocene NE-SW compression associated with tectonic accommodation of the South American Plate at circa 27-26 Ma, and responsible for WNW-ESE-trending sinistral and NE-SW-trending dextral strike-slip faults; (III) Plio-Pleistocene N-S to NNW-SSE compression related to dextral reactivation of NW-SE-striking faults, sinistral reactivation of NE-SW-trending faults, and generation of NNW-SSE-trending strike-slip faults; and (IV) Pleistocene-Holocene NW-SE to WNW-ESE compression that caused dextral reactivation of ENE-WSW-trending faults and sinistral strike-slip reactivation of NNW-SSE-trending faults.

ABSTRACT: The Paraná basin is one of the major morphotectures of the South American continent. Although its tectono-sedimentary evolution has been widely studied and fairly well understood, this paper aims to fill a gap in knowledge comprising the tectonic evolution after the end of its last sedimentary cycle, in the Upper Cretaceous. In this context, the Jordan River watershed, situated in the surroundings of Guarapuava municipality, south central region of Paraná State, was selected for structural and morphometric analysis where the Cretaceous volcanic rocks of Serra Geral Formation are exposed. The Jordan River watershed was studied for the influence exerted by Taxaquara Fault Zone on its morphologic evolution, since Taxaquara Fault Zone is associated to the Brazilian cycle and extends eastwards to the Ribeira belt in the state of São Paulo. The morphometric analysis consisted in the interpretation of the Jordan River watershed drainage network and relief elements, considering the distribution of existing knickpoints in the water courses. Structural analysis was based on the calculation of the stress fields responsible for the activation of local fault zones, which were determined by their spatial arrangement and the statistical and mechanical treatments of structural data. During the Oligocene and Miocene, erosional processes developed a planing surface which marks the relief in the central region of the Jordan River watershed and serves as a stratigraphic marker for the associated deformational events. Three events that contributed to the morphological framework of the Jordan River watershed were defined: an oldest one, probably active before the development of the Jordan pediplane in the Paleogene, by a NE-SW maximum horizontal stress (SHmax); and two more recent ones, being one of Plio-Pleistocene age, with a N05W SHmax, and a still active event of transtensive nature showing a N75W SHmax. The paleostress analysis points to a similarity between the Cenozoic evolution of Paraná Basin and the tafrogenic basins of southeast Brazil, revealing the amplitude of the deformation events associated to the studied period and ensuring the importance of further studies on the morphotectonic evolutions of intracratonic regions of the South American plate and their correlation to the Andean tectonic cycle.