An updated review of major-element geochemistry, redox systematics, and petrogenesis of the Märjamaa and Kloostri rapakivi granites, Estonia

The ~1.62 Ga Märjamaa and Kloostri rapakivi intrusions of western Estonia record a tripartite magmatic evolution during the late stages of the Wiborg rapakivi suite, emplaced in a transtensional pull-apart setting related to shear-zone reactivation during Nuna breakup and constructed through piston cauldron-subsidence processes. Whole-rock major-element geochemistry, complemented by CIPW normative phase relations, is used to constrain melt evolution, redox conditions, and crystallization patterns across three magmatic phases. Phase I formed as a deeply rooted intrusion that evolved into a piston cauldron structure through roof collapse and block assimilation, and comprises ferroan granodioritic to quartz-monzonitic compositions with lower silica and alkalis and elevated Ca and Fe–Ti–P-bearing components, reflecting relatively less evolved melts. Phase II intruded as a concentric granite ring during continued subsidence and represents the most fractionated stage, characterized by higher silica and alkalis, pronounced Ca depletion, and minimal normative Fe–Ti oxides and apatite. Phase III corresponds to the late Kloostri body emplaced by asymmetric subsidence and represents a Na-rich leucogranitic melt with the highest silica contents and the lowest abundances of Ca-bearing, Fe–Ti-bearing, and P-bearing components. Progressive differ entiation from Phase I to Phase III is reflected by systematic Fe-Mg trends, whereas redox conditions are more robustly constrained by iron speciation, indicating reduced conditions in Phase II, intermediate values in Phase I, and more oxidized conditions in Phase III. Decreasing normative Fe–Ti oxides from Phase I to Phase III primarily reflect progressive differentiation rather than solely oxygen-fugacity variations, emphasizing the semi-quantitative nature of redox constraints derived from major-element data. Theoretical thermobarometric estimates indicate mid-crustal crystallization at ~3–5 kbar with progressive cooling from Phase I to Phase III.