Stratigraphic and thermal constraints on the evolution of zeolite zonation in continental flood basalts: Insights from the Serra Geral Group, Paraná–Etendeka Magmatic Province

Zeolites are common secondary minerals in basaltic sequences, reflecting specific temperature ranges and hydrothermal or diagenetic processes. This study investigates the stratigraphic distribution and paragenetic evolution of Ca–Na–K zeolites within the Torres and Vale do Sol Formations of the Serra Geral Group, Brazil. To resolve common ambiguities in distinguishing heulandite from clinoptilolite, this research employs a geochemical discrimination criterion based on a framework Si/Al ratio > 4.0 rather than visual identification. Field observations and stratigraphic logging demonstrate a correlation between lava-flow architecture and alteration intensity, where vesicular and brecciated zones primary host secondary mineralization. Petrographic evidence reveals the replacement of volcanic glass and mafic phenocrysts by smectite and hematite, followed by the progressive infilling of porosity by zeolites. Integrated X-ray diffraction and electron microprobe analyses identify a distinct vertical zonation: laumontite predominates at basal levels, heulandite occupies intermediate intervals, and clinoptilolite is restricted to the upper stratigraphy. Chemical data show systematic variations in Si/Al ratios and extra-framework cations, reflecting fluctuations in fluid chemistry and thermal gradients. Equilibrium constraints indicate burial diagenesis followed by low-temperature hydrothermal alteration, with temperatures ranging from <100 °C in upper units to approximately 230 °C at the base. This vertical succession provides a robust framework for reconstructing the burial history and post-emplacement thermal evolution of the volcanic pile, offering insights into diagenetic processes in continental flood basalt provinces.