Capão do Leão Granite: Highly differentiated garnet‐bearing magmatism in the southeastern Dom Feliciano Belt, Brazil

Abstract

The Capão do Leão Granite (CLG; 583 ± 3 Ma) occurs as two NE‐oriented bodies, near the namesake city and Pedro Osório, Rio Grande do Sul, Brazil. The CLG is linked to the voluminous Ediacaran magmatism in the SE Dom Feliciano Belt (Pelotas Batholith), intruded in post‐collisional settings in the set of the non‐deformed younger plutons in the area. This work presents field characterization, petrography, mineral chemistry and whole‐rock geochemical affinities for the CLG. This granite exhibits miarolitic cavities, suggesting an epizonal emplacement, as well as mafic enclaves, which may represent source material, while mylonitic and S–C foliations are localized and post‐magmatic. The analysed samples are massive, leucocratic, coarse‐ to medium‐grained hypidiomorphic alkali‐feldspar granites composed of quartz, orthoclase (Or89–98), albite (An1–10), oligoclase (An11–16), garnet (Sps31–64 and Alm24–56), siderophyllite/annite, muscovite and Fe‐chlorite (secondary), apatite, epidote/zoisite, zircon, and opaques. The dispersion in mineral compositions in each occurrence and between them suggest different magmatic evolutionary trends. The diverse textures, zoning patterns and chemistry in garnet indicate both equilibrium with highly evolved Al2O3‐rich liquids, as well as a xenocrystic/restitic origin. The geochemistry shows subalkaline, high‐K, and metaluminous to weakly peraluminous fingerprints. Samples are commonly enriched in Rb, Th, U, Pb, Nd, and Sm, and depleted in Ba, Sr, Eu, Nb, P, Zr and Ti, due to advanced fractional crystallization. The classification of the CLG into some traditional chemical patterns is difficult, due to the high differentiation and the overlap of petrologic processes, although its derivation from I‐type liquids is proposed. The dispersion both in mineral and whole‐rock chemistry indicates different evolutionary trends for the CLG, where fractionation coupled with crustal recycling by assimilation/contamination processes were responsible for the granite differentiation.