ASPECTOS TECTÔNICOS FUNDAMENTAIS DO PROTEROZÓICO. MÉDIO NA AMAZÔNIA BRASILEIRA

Abstract

FUNDAMENTAL MIDDLE PROTEROZOICTBCRONIC FEATURES AT THE BRAZILIAN AMAZONREGION. The varied volcank, plutonic na sedimentary rocks of middle Proterozoic age are related to an extensional termo-tectonic event which affected all the Brazifiaa Amazon region.. The geometry and cinematics of the structural features and the basin fillings allowed to recognize two major extensional compartments. Several sets of NW-SE to WNW-ESE-trending normal faults with dips towards NE in the Eastern Compartment are observed, which formed mmiyhatf-grabenfi; some normal ftatoaseincUned to SW and form local symmetric grabens, like that of the Cachimbo. The transfer faults have consisted NE-SW direction, parallel to the extension axis. The K-Ar and Rb-Sr radiometric data point out younger ages from NE to SW, what is seen as due to the propagation of the normal faults by footwall coolapse in that sense. The Western Compartment normal faults sets with E-W direction, mostly Dipping to N. The transfer faults have N-S trend, parallel to the direction of the extension axis. As die Udwtogk units present younging firam S to N, one may infer the development of the fault system by hanging-wall coUapte is that sense. The Eastern and Western Compartments and western compartments are separated by the Boa Vista-Caracaraí Transfer zone. The normal Faults of both compartments and the Boa Vista-Caracaraí Transfer zone have concincident trends with the direction of earlier basament anisotropies. Such observation supports a reactivation of pre-existent structures as na important factor for the extensionalmovements and lithosphreic stretching factor was higher than 2, but tower dum S, and ft did not reach die value necessary for generation of oceanic crust The extensional event inverted toacompressiveoneatthebeggmingofthe Upper Proterozok, more noticeable in die Woman Compartment The normal faults were reactivated as upthrusts and die transfer zones as lateral ramps.