Zircon out, Elpidite in: Deformation-Driven Zirconosilicate Evolution in Peralkaline Granites: A Case Study of the Papanduva Pluton (Brazil)

The peralkaline granites of the Papanduva Pluton (South Brazil) display a remarkable facies dichotomy, with zircon dominant in massive facies and diverse zirconosilicates (Zr-Si) in foliated facies. This study employs petrography and mineral chemistry (major and trace elements) to elucidate the textural diversity and compositional evolution of these minerals. Three discrete zirconosilicate groups were identified: Na-rich elpidite ( euhedral, vein-like, and granular varieties), Na-poor (Na,K)Zr-Si-I, and silica-rich (Na,K)Zr-Si-II. Contrary to the expected crystallization sequences, trace element data reveal that REE enrichment correlates with deformation intensity rather than paragenetic order, with vein-like aggregates along deformation features showing the highest REE concentrations. Statistical analysis demonstrates significant correlations between REE contents and alkali exchange patterns. We propose a three-stage evolutionary model involving magmatic crystallization, deformation-enhanced fluid interaction, and late-stage recrystallization, with a progressive evolution from Na-dominated to K-dominated conditions. This study provides new insights into closed-system fluid evolution in agpaitic environments and highlights deformation as a primary control on element mobility in peralkaline granitic systems.