Phase equilibria constraints on crystallization differentiation: insights into the petrogenesis of the normally zoned Buddusò Pluton in north-central Sardinia

The Buddusò Pluton in NE Sardinia (Italy) is a normally zoned intrusion composed of three units with chemical composition ranging from hornblende-bearing tonalites (SiO2 ∼ 65 wt%) to leucocratic monzogranites (SiO2 ∼ 76 wt%). Zircon crystals in the pluton are dated at 292.2 ± 0.7 Ma and have εHf values ranging from −4 to −8, with no systematic differences observed between the units. The pluton, which is isotopically homogeneous at the whole-rock scale in terms of Sr and Nd isotopes, shows textural evidence indicating local crystal–melt segregation. In this paper, we have implemented a novel approach based on path-dependent phase-equilibria modelling to test the hypothesis that the internal chemical variability of the pluton was generated by crystallization differentiation of a homogeneous parental magma. Our modelling indicates that this hypothesis is valid if the mechanism by which this occurs is compaction in a rheologically locked crystal-rich magma and if the separation occurs at 0.3 GPa from a tonalitic magma with water content >2 wt%. Finally, a subset of the magmatic enclaves in the pluton are considered to be autoliths, formed by the disruption of the compacted crystal mush and interaction between these cumulates and the felsic melt.