Ortognaisses peraluminosos associados ao grupo araxá na região de rochedo, goiás

Abstract

In the Araxá Group metasediments in southern Goiás, there are occurences of numerous gnaissified granitic bodies. Two of these occurrences are located near Rochedo district, municipality of Piracanjuba. These two occurences show peraluminous, calc-alkaline composition, and are classified as S-type and/or MPG. These orthogneissic bodies have low to medium levels of alkalis, enrichment in large ion lithophile elements (Cs, Th, U, Ba, Rb, K), and LREE relative to HREE and to high field strength elements (Zr, Y, Nb, Ta, Hf). They also show negative anomalies of Nb, Ta, P and Ti, similar to the chemical composition of magmas generated in magmatic arcs. The geochemical similarity in the distribution patterns of LILE, HFSE, REE and the presence of anomalies of Nb, Ta, P and Ti in samples of the Araxá Group metasediments and of the orthogneisses suggest that the Rochedo orthogneisses derived from partial melting of Araxá Group metasediments. The geochemical and isotopic data for rocks of the region, in congruence with the geological context, indicate that the source rock of these metasediments were formed in magmatic arcs and that they were deposited in backarc type basins, developed on the margin of the Neoproterozoic island arcs.