Grenvillian age magmatism in the Southern Espinhaço Range (Minas Gerais): evidence from U-Pb zircon ages
This paper describes the first in situ occurrence of a volcanic rock with maximum deposition age of ca. 1.16 Ga suggesting a Grenvillian (~ 1.4 - 1.0 Ga) magmatic event in the Southern Espinhaco Range. Sample Vul-1A is intrusive within the Archean Basement Complex, and is characterized by a brecciated structure, with clasts of schists, banded iron formations (BIFs), volcanic and granitic rocks, in a very fine to medium-grained matrix. Petrographically, it has a basic nature with alkaline tendency, defined as a basaltic trachyandesite to trachybasalt, with volcaniclastic aspects. Zircons recovered from the matrix of this rock showed three types of ages: Archean ages (mainly between 2.9 - 2.7 Ga), Paleoproterozoic ages (2.2 - 1.8 Ga), and the most important, Grenvillian ages (1.20 - 1.16). Geochemical data showed that this unit is not similar of the post-Espinhaco meta-basic rocks (Pedro Lessa Suite), dated at 1.0 - 0.9 Ga. If the occurrence of an igneous rock of that age is confirmed, with such facies aspect, it reinforces the idea that similar magmatic processes possibly of explosive type occurred during the last syn-rift phase of the Espinhaco basin evolution. Our geochronological data may have identified the possible source of the Grenvillian detrital zircons from the Sopa-Brumadinho Formation, and suggest that these volcanic processes were coeval and recurrent during the sedimentation of this unit.