NEOTECTÔNICA DA PLATAFORMA BRASILEIRA: ESBOÇO E INTERPRETAÇÃO PRELIMINARES

Abstract

A number of significant informations about the evidences and characteristics of a neotectonic activity in the Brazilian Platform have been gathered in the last year in different parts of the country. These permit the definition of main structural features due to reactivation of Precambrian geossutures: Crustal Descontinuity of the Two Brazils (CDTB), Crustal Descontinuity of the Right Amazonian Margin (DCMDA), Minas- Alagoas Crustal Descontinuity (DCMA), Tocantins-Araguari Crustal Descontinuity (DCTA), Crustal Descontinuity of the Upper São Francisco (DCASF), Crustal Descontinuity of the Upper Rio Grande(DCARG), Crustal Descontinuity of the Pernambuco Lineament (DCLP), Crustal Descontinuity of the Midle-Upper Paraná (DCMAP), Crustal Descontinuity of the Paraíba do Sul (DCPS).

In many of them, continental rifts and individual sedimentary basins have been generated. Some were submitted to a younger compression, resulting in its tectonic inversion. These main discontinuities control the macrorelief and the regional drainage pattern, as well as the orientation and subdivision of the main hidrographic basins.

Blocks limited by these discontinuities are fragmented by faults of different types and sizes resulting in a regional structure alternating subsidence and uplift.

The western extremity of the Amazon Basin is partially disrupted by blind inverse faults related to the Andean Orogeny. The central and Eastern areas are cut by Riedel Shears due to E-W dextral shearing.

The oriental coastal province displays different patterns from south to north. The southern and southeastern regions, are dominated by Cenozoic uplift with tilting of blocks to W and NW and domnwarping of the off-shore blocks. In the Northeastern region morphological doming is related to transpressive conditions due to E-W dextral shears.

The geological and seismological data indicate horizontal, roughly NW-SE oriented compressive stresse at least in the N, NE and Center- SE areas. Gravimetric data confirm the morphotectonic interpretation.