Análise petrográfica e proveniência dos metassedimentos do Complexo Pontas do Salso, Terreno São Gabriel, Cinturão Dom Feliciano, RS

The Pontas do Salso Complex occurs in the south part of the Sao Gabriel Terrane, western portion of the Dom Feliciano belt, center-west of the Rio Grande of South. To evaluate the stratigraphic relationships and characterize the units of the complex was carried out a detailed geological and structural mapping, with collection of samples for petrographic analysis, assessment of relations between metamorphism and deformation and modal count of the constituent minerals to define the provenance of the metasediments. The Pontas do Salso Complex consists of meta-arkoses with subordinate occurrence of metaconglomerates and metapelites. The meta-arkoses presents fine to coarse blastopsamitic texture with porphyroclasts of hexagonal quartz and plagioclase. The polimitic metaconglomerates are matrix supported and show between 15 and 55 % of the clasts. The pelitic rocks are mainly composed of muscovite phyllites. The analyzed samples were classified as arkoses and lithic arkoses and the majority of the arenites fell on the field of Dissecated Arc. The orogenic metamorphism developed clorite, biotite/cloritoid and garnet zones, defining Upper greenschist to amphibolite facies conditions. The metasediments were still subjected to thermal metamorphism, however, the sedimentary structures and the volcanogenic and granitic sources are preserved. The presence of clasts of tonalites and granodiorites related to Lagoa da Meia Lua Suite suggests that the deposition of the metasediments is posterior to the emplacement of the units of this suite, whose U-Pb SHRIMP zircon ages are between 690 to 680 Ma.