Geoquímica elementar com ênfase em elementos terras raras em mármores do bloco São Gabriel no escudo Sul-rio-grandense

Abstract

The present dissertation presents petrographic and litoquímicos results of calcitic and dolomitic marbles collected in four distinct areas of the São Gabriel Block, which follow: (i) Batovi area, (ii) Palma Area; (iii) Passo Feio Area; and (iv) Porongos Area. The set of marbles that appear in these areas make up a mineralogically homogeneous group. The carbonate predominates largely of the modal composition of these rocks. However in some areas where there are magnesian minerals such as serpentine and talc, there may be a tendency to dolomite. After analyzing and tabulating data of the samples of calcitic and dolomitic marbles, a prospective criterion was established for the marbles of the São Gabriel Block, where it was possible to separate two populations of marbles. The first one consists of the areas (i) Batovi and (ii) Palma with marbles of predominantly Calcitic composition and a second population of predominantly dolomite marbles, composed of (iii) Feio and (iv) Porongos areas. On the other hand, the geochemical study, through the Rare Earth Elements in the Metassedimentary sequence of carbonate origin, found that samples presented negative anomalies of Cerium and positive of Eu. Regarding the negative anomaly of Ce, this occurs due to the low concentration of Rare Earth Elements of sea water. This Ce anomaly is a consequence of Ce + 4e and Ce + 3, having a large Eh-Ph stability field. The negative anomaly of Ce in sedimentary rocks, particularly in carbonate rocks, has been commonly used as an argument of marine origin, while its absence is attributed to the influence of continental waters, particularly for carbonate rocks. As for the positive anomaly of Eu in marine sediments and in sea water, this has been attributed to a hydrothermal flow.