Are The Large Wave-Lenght South American Intraplate Deformation And The Incipient Inversion Of Brazilian Continental Basins Manifestations Of Ongoing Lithospheric/ Crustal Folding?

The South American plate (SAP) is now in horizontal compression and shortening. This is shown by stress data<br>compilations, intraplate stress field numerical models and space-based geodetic results. Thrust regimes prevail in SE<br>Brazilian margin, Central Brazil and Amazon region; strike slip regimes prevail in NE Brazilian margin<br>(Assumpção, 1998). In most Brazilian basins, breakout orientations are usually consistent for the World Stress Map<br>qualities A, B and C, allowing a good estimate of the regional maximum horizontal stress (SHmax), which is in general in<br>good agreement with the available nearby focal mechanisms (Lima et al., 1997). Available stress magnitudes derived<br>from hydrofracturing and leak-off testes have shown that strike-slip stress regimes prevail within the Potiguar and the<br>Campos basin (Lima Neto, 1998 ; Lima Neto & Beneduzzi, 1998). Results from the French geodetic space-based system<br>DORIS are consistent with the observed ongoing compression since all but one of the available base-lines are<br>shortening. Base lines that cross the Andes towards the intraplate are shortening 13-20 mm/yr; intraplate shortening<br>between Cachoeiro Paulista (SE Brazilian coastal ranges) and Kourou (French Guyana) is about 7 mm/yr (L. Soudarin,<br>CNES, Toulouse, written communication). Geodetic results have also confirmed that the Andean belt is still moving<br>eastwards, thrusting the Brazilian craton (Norabuena et al, 1998). The compression / shortening is probably due to the<br>interactions amongst the SAP and its neighborhood (mostly its convergence with the Nazca and the Caribbean plates<br>and its divergence from the African plate) and with the asthenosphere as well (Cobblentz &Richardson, 1996 ;<br>Silver & Russo, 1996).