Summary
Amazonian Precambrian has been subdivided on three larger intervals: Upper, Middle and Lower, separated by the 2.600 m.y. and 1.800 m.y ages. Many CPRM's works, together with RADAM Project informations, made possible a new subdivision for the Precambriam time. Thus, likewhise Canada, URSS, Australia, South Africa and China's scales, two major intervals compound Precambrian: Archaeozoic and Proterozoic. The former enclose two chief tectonic cycles, one of then take place at Lower Archaeozoic (over 3.000 m.y.), called Guriense, and other related to Upper Archaeozoic (2.600 m.y. to 3.000 m.y.) and named Aroense (2.600 m.y. to 2.600 m.y.). Rocks belonging to granulite facies represents Guriense Cycle, like Iniataca Complex in Venezuela, whereas anfibolitic belts as well as Anauá (Roraima), Cuiú-Culú (Pará): Moura (Amazonas), Kanuku (Guiana), Supamo (Venezuela) and Coeroeni (Suriname) where metamorfised during Aroense Cycle. In Lower Proterozoic (2.600 m.y. to 1.900 m.y.) Transamazonian Orogenic Cycle has been developed (2.000 to 2.200 m.y.), producing many greenstone belts and itabiritic rocks like so called Cauarane (Roraima), Tunuí (Amazonas), Grão Pará (Pará), Vila Nova (Amapá), Barama (Guiana), Pastora (Venezuela), Armina (Suriname) and Orapu (French Guyana) Groups. This is the last orogeny to affect the Amazonian region, since thenceforth, all evolutive process In Plataform possessed cratogenic character. Two principals Plataform's reactivations took place during Middle Proterozoid, one at ± 1.800 m.y. (Uatumã), and other at 1.500 m.y. (Parguazense). well known by intensive acid magmatism. The boundary between Middle and Upper Proterozoic is established at ± 1.200 m.y., whith the Tectonic Episode K'Mudku development. Other important reactivation, make possible many plutonlc intrusions, at the Upper Proterozoic beginning (Rondoniense granites), adjoining and closely related with alkalibasalt extrusion of the Pacaás Novos (Rondônia), Lábrea (Amazonas) and Cachoeira Seca (Pará) types. At the Proterozoic final, another and poor known reactivation may correspond to Brasilian Cycle, englosing alkalic magmatism (Guariba Alcalines) and arkose sedimentation (Prosperança Formation).