Age and petrogenetic constraints of the post-collisional Parati Granite, southeast Brazil

Abstract

The Ribeira orogen is one of the orogens formed in the Pan-African-Brasiliano collisional event. Post-collisional Cambrian-Ordovician magmatism occurred after the main agglutination event of this orogen, being recorded in its central segment by a series of granitic bodies exhibiting few or no deformation, which have been divided into three suites, Suruí, Nova Friburgo and Sana. This work brings a contribution to the understanding of the generation of these bodies through the geochemical - petrological study of the Parati Granite. In addition, unpublished data about crystallization temperature and pressure conditions during the emplacement, as well as a proposition on source and generation model for this granite is also presented. The Parati Granite has a batholithic size showing a predominant inequigranular porphyritic facies with feldspar phenocrysts, besides another inequigranular to equigranular facies also composed of feldspar, quartz, biotite, hornblende and titanite. Geochemically, it is a high potassium, Hi-BaSr metaluminous, magnesian to slightly ferroan calc alkaline granitoid. REE and multielemental diagrams along with biotite composition suggest that Parati Granite was generated from crustal melting with involvement of an enriched mantle, which is corroborated by isotopes of Sr, Nd and Hf. Geothermobarometry results point to crystallization temperature ranging from 760° to 810 °C and pressures varying from 3 to 5 kbars. Geochronological data indicate crystallization age interval between ca. 520 to 505 Ma. Due to the similarities of geochemical patterns and isotopic data, it is believed that the source of this granite could be rocks of the Rio Negro Arc. As a geodynamic model, slab breakoff followed by uplift can be considered as a mechanism responsible for the formation of Parati Granite, as it explains its mantle and crustal signatures.