Unravelling magmatic evolution and mixing through mineral chemistry: insights from the Riacho do Mingu syenitic stock, Macururé Domain, southern Borborema Province, Brazil

The Riacho do Mingu Stock (RMS) is a syenitic intrusion with evidence of mixing, located in the northern part of the Macururé Domain. In the syenites, a porphyritic texture occurs with alkali feldspar phenocrysts embedded in a matrix composed of biotite, amphibole, plagioclase, and quartz. Enclaves in the RMS are predominantly micaceous, with amphibole and plagioclase. The plagioclase crystals from the stock exhibit variations in X_An content from 0 to 17 % in the syenites and from 0 to 47 % An% in the enclaves. By applying physicochemical parameter inference equations available in the literature for amphibole crystals, pressures of 2.5–4.8 kbar were identified in the syenites and from 2.4 to 9.1 kbar in the enclaves, suggesting greater depths for the mafic magma. Estimated temperatures range from 672 °C to 876 °C in the syenites and from 675 °C to 830 °C in the enclaves. The biotite crystals crystallized between 585 °C and 646 °C at pressures of 0.9–2.3 kbar. The amphibole chemistry data in the enclaves suggest a mantle origin for most specimens, while some crystals may have incorporated crustal material. The amphibole in the syenite has a mixed mantle-crust source. The higher temperature in the enclaves may reflect an origin in a mantle magma that came into contact with the trachytic liquid of the chamber at around 18 km depth. The studied biotite points to magmas of calc-alkaline affinity, reinforcing a collisional environment with a mixture of crustal and mantle sources. Until now, syenitic rocks with features belonging to the Serra do Catu Suite had not been found in the Macururé Domain; being previously restricted to the Canindé Domain, located further north. Therefore, the presence of unique features is observed in the Macururé Domain, representing a contribution to the southern portion of the Borborema Province.