LAUSR

Magma mixing and contamination are among the dominant processes in the building of the isotopic diversity of granite rocks. Felsic microgranular enclaves (FMEs) are remnants of magma mixing and they often carry xenocrysts that also record contamination and assimilation in crystallization fronts disrupted during replenishment events. In addition to isotopic changes, contamination may alter the redox state of the intruding magmas depending on the nature of the country rocks. We investigate the role played by different country-rocks on the redox trajectory of the precursor magmas of two Brazilian occurrences: the Mauá pluton, which intruded sulfide- and graphite-bearing metasediments, and the Salto rapakivi pluton, which intruded orthogneisses. Oxygen fugacity ( f O 2 ) was estimated using Eu 2+ /Eu 3+ ratios retrieved from plagioclase chemistry and literature equation that considers melts chemistry and temperature. The model is demonstrated to replicate the f O 2 from plagioclase-bearing experimental data within a precision usually better than 1 log unit. Results obtained for the Mauá pluton indicate that contaminated plagioclase cores are significantly more reduced (∆QFM − 1.5; 87 Sr/ 86 Sr ~ 0.713) than the xenocryst rims (∆QFM + 0.5; 87 Sr/ 86 Sr ~ 0.710). In contrast, results obtained for the Salto rapakivi pluton vary from ∆QFM + 1.0 to ∆QFM + 2.7 and do not coincide with core to rim variations in 87 Sr/ 86 Sr. MMEs are comparatively more reduced (− 0.1 ≤ ∆QFM ≤  + 0.7). Our results imply that the redox path registered by plagioclase crystals from different geological backgrounds reflects the nature of their country rocks and the processes that affected their precursor magmas The main advantage of using plagioclase trace element data to model redox conditions of equilibrium magmas is the possibility of determining f O 2 paths via spatially controlled trace element analyses of crystals rims and cores. Coupled to the possibility of obtainment of Sr isotope data, the model represents a powerful way to unravel the processes responsible for redox paths of magmatic rocks of varied nature.