Sana Granite, a post-collisional S-type magmatic suite of the Ribeira Belt (Rio de Janeiro, SE Brazil)

Abstract

The postcollisional magmatism in the Ribeira Belt, a collisional Orogen developed through several episodes during the convergence of the Pan-African/Brasiliano Orogeny, was marked in the Eastern Terrane (Rio de Janeiro, SE Brazil) by intense granitic magmatism of Cambro-Ordovician age. This magmatism was previously divided into the Suruí and Nova Friburgo suites, both interpreted as I-type granites generated by the interactions of magmas with crustal and mantle origins. This paper presents a new contribution to the understanding of the Sana Granite. It is based on the analysis of field work, mineralogical and geochemical (elemental concentrations by Inductively Coupled Plasma Emission Spectrometer, ICP-ES, and Inductively Coupled Plasma Mass Spectrometry, ICP-MS) data, and U–Pb dating and Lu–Hf isotope analyses, by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) from the main body and one satellite of the Sana Granite. The results of this work show that the Sana Granite, previously grouped with the Nova Friburgo suite, presents petrographic, geochemical, and isotopic characteristics that do not match its initial petrogenetic interpretation. Data from this work show that the Sana Granite is composed of alkali feldspar granites, syenogranites and monzogranites. All these rocks are hololeucocratic to leucocratic, with small grains ranging from fine to coarse. They are silica-supersaturated, peraluminous, and mostly alkali-calcic rocks and plot at the limit between the ferrous and magnesian fields. Crystallization ages of 480 ± 6 million years (Ma) and 495 ± 4 Ma are obtained in the main body of the Sana Granite, while the ages obtained in the satellite body are 506 ± 10 Ma and 508 ± 5 Ma. The Hf isotope data indicate crustal sources, with depleted mantle model ages (TDM) varying between 2.22 and 1.69 Ga and εHf values ranging between −15.54 and − 6.54. The data set from this work suggests that Sana is an S-type granite formed by the partial melting of metasedimentary rocks from the dehydration of hydrous minerals, such as biotite and muscovite. This massif is composed of muscovite-bearing peraluminous granitoids (MPGs) associated with high-pressure collisional Orogens. Considering that the characteristics of the Sana Granite are incompatible with those of the Nova Friburgo suite, it is proposed to use the Sana suite to characterize S-type granites generated in the postcollisional stage of the Ribeira Belt.