The Late Neoproterozoic granitoid magmatism of the Pelotas Batholith, southern Brazil

摘要

Geological mapping, petrography, geochemistry, and isotope studies enable the division of the Pelotas Batholith into six granitic suites: Pinheiro Machado (PMS), Erval (ES), Viamao (VS), Encruzilhada do Sul (ESS), Cordilheira (CS), and Dom Feliciano (DFS). The rocks of the PMS show a large compositional range (granite through granodiorite to tonalite), and the suite is considered pre- to syncollisional. Other suites show restricted compositional variations (granite to granodiorite) and are late to postcollisional. In general, the suites are metaluminous to slightly peraluminous (PMS, ES, and VS) or peraluminous (CS) or have alkaline tendencies (ESS and DFS). The magmatic evolution corresponds to high-K calc-alkaline to alkaline magmatism. The suites are enriched in K, Rb, and REE compared with rocks of typical calc- alkaline series. Initial ~(87)Sr/~(86)Sr ratios vary from 0.705 to 0.716, except in the CS, where they attain values of 0.732-0.740. Sm-Nd T_(DM) model ages vary between 0.98 and 2.0 Ga, with initial ε_(Nd) values ranging from -0.3 to -10. U-Pb zircon dates of samples from PMS, VS, and ESS suggest an age between 0.63 and 0.59 Ga for magmatism. Rb-Sr dates of samples of alkaline granites from DFS present ages between 0.57 and 0.55 Ga. The main tectonic controls of the magmatism of the Pelotas Batholith are high-dip sinistral shear zones.