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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 NNWSSE-trending strike-slip faults; and (IV) Pleistocene-Holocene NW-SE to WNW-ESE compression that caused dextral reactivation of ENEWSW- trending faults and sinistral strike-slip reactivation of NNW-SSE-trending faults. [ABSTRACT FROM AUTHOR]

The hypothesis that geomorphometric parameters and structural-geological features are diagnostic of reactivation of the Blumenau-Soledade Lineament in central-western Santa Catarina, Brazil was tested by confronting data on asymmetry, elongation, morphological markers, drainage patterns, and river anomalies of the Pelotinhas catchment and structural data for the Serra Geral Group (Paraná Basin). The results indicate reactivation of the lineament as a dextral strike-slip fault, as the cause of an associated morphostructure characterized by an escarpment along the left bank of the river as well as being responsible for catchment asymmetry and morphometric anomalies. Although fault data indicate paleostress correlatable to regional tectonic events described in the literature, we propose that the earliest paleostress pulse possibly was active during the Paleocene-Eocene transition, with s1 oriented NE-SW and s3 NW-SE. In the early Paleogene, the stress system evolved as an extensional pulse. During the Paleogene and early Neogene, the paleostress field rotated with reorientation of the s1 axis between NNW and NNE. The current tectonic regime was established between the Late Pleistocene and Holocene, with compressional stress s1 oriented approximately WNW-ESE and s3 NNE-SSW, as it generally occurs in the South American Plate. [ABSTRACT FROM AUTHOR]