The Araras Escarpment in the upper Paraná River: implications to fluvial neotectonics on the Paraná drainage net evolution

Resumo

The Paraná River hydrographical basin, the second largest in South America, has in its upper reach an anomalous geomorphological structure, in relation to the general NNE-WSW channel direction. This anomaly occurs south adjacent to the Rio do Peixe river mouth, where the Paraná River makes a U turn controlled by an unique antithetic fault block dipping W. This alteration occurs against the general pattern of the synthetic fault blocks dipping E of its left margin. This anomalous pattern is in accordance to the presence of a NW-SE shear megazone ruled by the Guapiara lineament. Geomorphological data and location of some clay deposits within this region indicate a previous and more ancient channel for this river according with the general NNE-WSW direction of the Três Lagoas Crustal Suture Zone. This new U pattern was formed only after the occurrence of a neotectonic reactivation at the crossing point among the Guapiara Lineament and the Três Lagoas Suture Zone. It is here assumed that the lineament mode N350º appears as the most probable hydraulic tensor of this region and represents the distensional direction. The lineament swarming N315º and N40º, as well as those grouped together in mode N115º, may favor transcurrent dextral movements for the NW quadrant and sinistral for the other two directions with transtensive and transpressive deformation. Both are dependent on the local geometry of fracture plains and local stress fields. The most ancient geochronological data obtained until now for seismic liquefaction structure samples from the Rio do Peixe valley, suggest a date of 34 ka BP, indicating that this tectonic regime was still active at this time.