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.
Highlights
The collision between continental masses during the formation of supercontinents triggers the closing of oceans in subduction zones and the generation of magmatic arcs with intense production of granitic magmatism (Trompette 1994)
According to Oliveira (1998), the Riacho do Pontal Fold Belt is divided from south to north in three domains with distinct lithological and tectono-metamorphic characteristics
The Serra das Melancias Pluton exhibits high-K alkaline to shoshonitic affinities, similar to post-collisional or late-orogenic suites affected by subduction-precedent events, as defined by Bonin et al (1998)
Summary
The collision between continental masses during the formation of supercontinents triggers the closing of oceans in subduction zones and the generation of magmatic arcs with intense production of granitic magmatism (Trompette 1994). The Riacho do Pontal Fold Belt is composed of an ample suite of magmatic rocks marked by intense deformation and metamorphism Among these rocks, a basement formed by tonalite-trondhjemite-granodiorite (TTG) migmatites and granitoids, amphibolite-facies metasedimentary and meta-volcanosedimentary sequences stands out, not to mention syn-, late- and post-collisional magmatic intrusions of granitic to syenitic composition (Brito Neves 1975, Caxito 2013). The intrusive bodies that belong to this magmatism are situated in the southern margin of the Parnaíba Basin and were named Serra da Aldeia Suite by Gava et al (1984) These plutons are oval to circular, trend approximately NE-SW, and are considered as the last magmatic event of the Riacho do Pontal Fold Belt (Caxito 2013, Brito Neves et al 2015)
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