U-PB LA-ICP-MS and geochemical data of the Alto Chapéu Pluton: Contributions on bimodal post-collisional magmatism in the Araçuaí belt (SE Brazil)

Abstract

Bimodal inversely zoned plutons were emplaced at the late stages in the Araçuaí Belt, composing a tectonic corridor following the Atlantic coast of Brazil. This work presents original geochemical and geochronological data from the Alto Chapéu pluton, a post-collisional pluton that belongs to the G5 Supersuite of the Araçuaí belt. It comprises inequigranular porphyritic granites and fine grained (monzo) diorites, showing transitional alkaline to calc-alkaline to subalkaline signature, wide silica range, metaluminious I-type character with low MgO, moderate to high alkali contents and enrichment in LREE. They are classified as monzodiorites, quartz syenites and granites. The monzodiorites and syenites present a discrete negative Eu anomaly, in contrast to the granites. In Harker diagrams, syenites plot between the granites and mozodiorites, defining a linear trend, suggesting chemical mixing between two contrasting magmas. A coherent trend in Harker diagrams with Santa Angélica samples, a neighboring pluton, suggests a cogenetic character between both bodies. U–Pb LA-ICP-MS zircon data yielded two concordia ages of 641 ± 5 Ma and 531 ± 4 Ma, both interpreted as magmatic crystallization. The first is related to inherited crystals from the host rock (Estrela orthogneiss), which is considered in the literature as correlated to the pre-collisional event, and the former is interpreted as crystallization age of the Alto Chapéu pluton, chronocorrelated with Araçuaí belt post-collisional event.