Geochemistry of the Serra das Melancias Pluton in the Serra da Aldeia Suite: a classic post-collisional high Ba-Sr granite in The Riacho do Pontal Fold Belt, NE Brazil

Abstract

ABSTRACT:The Serra da Aldeia Suite is composed by circular or oval-shaped plutons, intrusive in meta-sedimentary and meta-volcanosedimentary rocks in the Riacho do Pontal Fold Belt, NE Brazil. The Serra das Melancias Pluton, belonging to Serra da Aldeia Suite, is located southeastern of Piaui state, near Paulistana city. These plutons represent a major magmatic expression in this area and contain important information about the late magmatic/collisional geologic evolution of the Brasiliano Orogeny. Based on petrographic and geochemical data, three facies were defined in the Serra das Melancias Pluton: granites, syenites and quartz monzonites. The rocks display high-K and alkaline to shoshonitic affinities, are metaluminous and show ferrous character. They are enriched in Light Rare Earth Elements and Large Ion Lithophile Elements, with negative anomalies in Nb, Ta and Ti. Their high Ba, Sr, K/Rb, low Rb, relatively low U, Th, Nb to very low Heavy Rare Earth Elements and Y resemble those of typical high Ba-Sr granitoids. The geochemical data suggest the emplacement of Serra das Melancias Pluton in a transitional, late to post-orogenic setting in the Riacho do Pontal Fold Belt during the late Brasiliano-Pan African Orogeny.KEYWORDS: alkaline granites; geochemistry; Riacho do Pontal Fold Belt; Borborema Province; high Ba-Sr granites. RESUMO: A suíte Serra da Aldeia é composta por plútons graníti-cos circulares ou ovalados, intrusivos em sequências metassedimentares e metavulcanossedimentares na Faixa Riacho do

P-T evolution of metasedimentary rocks of the Santa Filomena Complex, Riacho do Pontal Orogen, Borborema Province (NE Brazil): Geothermobarometry and metamorphic modelling

“…It is constituted of meta-psammo-pelites intercalated with metatuffs, metabasalts and metarhyolites, and is intruded by a layered meta-ultramafic sequence (Salgado et al, 2016), and granitic rocks of alkaline affinity (Serra da Aldeia Suite). Caxito (2013) and Brito Neves et al (2015) suggest that the metamorphism of the Rajada syn-colisional gneisses was generated during the Brasiliano/Panafrican Orogeny in the Late Neoproterozoic, and the intrusion of sub-alkaline to alkaline granites of the Serra da Aldeia Suite in a post-orogenic crustal relaxation phase of the orogeny (Perpetuo et al, 2016). Regarding the sedimentation age of the Santa Filomena Complex metasedimentary rocks, Brito Neves et al (2015) and Santos et al (2017) obtained important detrital zircon population data around 750 Ma, suggesting a maximum age of deposition in Late Neoproterozoic for the Complex.…”

“…Such E-W structuration is marked by strong compressive and transpressional tectonic with vergence to the São Francisco Craton (Brito Neves, 1975;Angelim, 1988;Jardim de S a et al, 1992;Angelim and Kosin, 2001). Despite the recent advances regarding the geologic history of the Riacho do Pontal Orogen (Caxito, 2013;Caxito et al, 2014aCaxito et al, , 2014bCaxito et al, , 2016Brito Neves et al, 2015, Perpetuo et al, 2016Salgado et al, 2016), studies focusing on the tectono-metamorphic history (P-T evolution) are still scarce and deserve more consideration, because they provide valuable information on orogenetic processes (Spear et al, 2008;Brown, 2014). In this sense, we present petrographic and mineralogical data on the metamorphic evolution of the metasedimentary rocks (schists and paragneisses) of the Santa Filomena Complex in the Riacho do Pontal Orogen.…”