Petrogenesis of the F-rich peraluminous A-type granites: An example from the Devonian Achala batholith (Characato Suite), Sierras Pampeanas, Argentina

Abstract

The Characato suite (Achala batholith, Sierras Pampeanas, Argentina), consists of at least six granitic facies with affinities of F-rich moderately to strongly peraluminous A-type granites. The two more extensive facies (Facies 1 and 2) and a minor one (Facies 5) would represent at least three batches of magma generated by partial melting from the same source but at different times and under different P-T conditions. Previous and new U-Pb zircon ages for the Characato suite suggest that these granites crystallized between 366 ± 3 and 359 ± 5 Ma. U-Pb inherited zircon ages, Th/U ratios and the whole-rock Sr-Nd isotopic compositions indicate that the source is predominantly composed of Early Cambrian S-type granites and diatexites and minor Early Ordovician TTG granitoids, which formed part of the Devonian deep crust of the Sierras de Córdoba. Mineral saturation thermometers, phase equilibrium modeling and trace element modeling suggest that the Facies 1 comprise magmas generated at ~ 0.5 GPa and ~805°C and least evolved Facies 2 (+ Facies 5) comprise magmas generated at ~ 0.7 GPa and ~870°C: both could represent low proportions of pure melts (~10% to ~20%) that contain minor amounts of entrained residual mineral phases. Fractional crystallization models may explain the chemical variation in the evolved granitic samples (Facies 2, 3, 4 and 6) by fractional crystallization of plagioclase, K-feldspar, quartz, biotite, muscovite, zircon, monazite and Fe-Ti-oxides. Facies 6, composed of high evolved granitic rocks, probably represents the late stages of the fractional crystallization process where late fluids interacted with the magmas.