Geologia, petrografia e geoqu?-mica das associa?§?μes leucogran?-ticas arqueanas da ??rea de Nova Canad??: Prov?-ncia Caraj??s

摘要

Nova Canad?? area is marked by the occurrence of two leucogranite varieties that, despite their petrographic affinities, show strong geochemical contrasts. Nova Canad?? Leucogranodiorite is more expressive and composed of leucogranodiorites and leucomonzogranites of seriated texture from moderate to weak degree of recrystallization, while Velha Canad?? Leucogranite is more enriched in modal quartz, has medium even-grained texture and is from moderately to strongly deformed. In addition, the geochemical behaviour shows that Nova Canad?? Leucogranodiorite rocks are enriched in Al 2 O 3 , CaO, Na 2 O, Ba, Sr, have high Sr/Y ratios and slightly fractionated REE pattern, with low (La/Yb) N ratios and absence of negative Eu anomalies. In contrast, Velha Canad?? Leucogranite shows higher contents of SiO 2 , Fe 2 O 3 , TiO 2 , K 2 O, Rb, HFSE (Zr, Y and Nb), and K 2 O/Na 2 O, FeOt/(FeOt+MgO), Ba/Sr and Rb/Sr ratios, being more enriched in REE and characterized by (i) moderate to low (La/Yb) N ratios, with accentuated negative Eu anomalies; (ii) moderate to high (La/Yb) N ratios, discrete Eu anomalies and a concave shape with HREE patterns. Such geochemical contrasts suggest a distinct origin to these rocks. Nova Canad?? Leucogranodiorite has less evolved characteristics related to mantle and crust geochemical signature (high Ba-Sr), while Velha Canad?? Leucogranite has stricto sensu characteristics (high-K), being more evolved and similar to the granites originated by crustal anatexis. The geochemical affinities between Nova Canad?? Leucogranodiorite and the rocks of Guarant?￡ Suite from Rio Maria Domain suggest that they could be related to the same magmatic event. Velha Canad?? Leucogranite shows affinities with various high-K calc-alkaline granites of Caraj??s Province. Even without a clear chronological relation, its deformational pattern is typical from the Neoarchean, which could relate it to the same tectonomagmatic event that affected Cana?￡ dos Caraj??s Domain in that period.