| Popis: |
This paper presents and discursses some of the last geochronological determinations carried out on rocks of the Espinhaco Mountain Belt; by different radiometric methods. For the most part, the basement is composed of Archaean rocks, with formation of magmatites and granites during the Transamazonian cycle (2,0 b.y.). The geologic evolution of the Chapada Diamantina Group is proposed as follows: 1- At 1,7 b.y. formed the first sedimentary basins, associated with continental acid voleanism. 2 - The main stage of folding and epizonal metamorphism occured at approximately 1,2 b.y, with post-tectonic events until 1,0 b.y. These last ones include basicfissure volcanism and tectonic uplift. 3 - During the Brazilian cycle (650-400 m.a.) the tectonothermal phenomena have affected in several ways and with different intensity the age determinations of all geological units. |
