Tectonic drivers and melt evolution: Unravelling the genesis of pegmatites in the Eastern Brazilian Pegmatite Province

The Eastern Brazilian Pegmatite Province (EBPP) hosts a diverse array of pegmatites with significant economic and scientific interest, ranging from rare-element pegmatites enriched in Li, phosphate- and boron-bearing assemblages. These pegmatites are closely associated with S-type granites and metasedimentary host rocks, forming complex magmatic-hydrothermal systems. The Urucum and Itatiaia pegmatites exemplify this late-stage magmatic evolution, displaying distinct geochemical and isotopic signatures reflecting their different fractionation degrees, crustal contamination, and parental melt evolution. We investigate their petrogenesis through U-Pb geochronology, trace element geochemistry, and Sm-Nd isotope analyses of apatite, cassiterite, and zircon to refine their genetic relationships with associated granitic systems and assess the role of partial melting, fluid-rock interaction, and post-collisional magmatism in pegmatite genesis. Our results indicate a temporal and genetic decoupling between the pegmatites and their associated granites, with pegmatite crystallisation occurring ∼ 50 Ma after granite emplacement. The EBPP cannot be explained solely by fractional crystallisation but rather involves partial melting and crustal remobilisation during the post-collisional stage. The Itatiaia pegmatite exhibits an evolved geochemical signature, suggesting a distinct melt evolution influenced by crustal contamination, while the Urucum pegmatite retains geochemical characteristics similar to the G3 S-type granites. Nd isotopic data support a Paleoproterozoic crustal source, with pegmatites forming during the post-collisional stage of the Araçuaí orogen (∼530 Ma). The EBPP developed through a multi-stage tectono-magmatic evolution, transitioning from syn-collisional S-type granites at ∼ 580 Ma to post-collisional anorogenic granite and pegmatite formation between 530 and 500 Ma in the core of the Aracuai orogen, SE Brazil. This transition was characterised by anorogenic magmatism and extensional tectonics driven by orogenic collapse, facilitating the generation of highly evolved pegmatitic melts.