Cryogenian magmatic arc detrital ages and superposition of metamorphic events in metasedimentary rocks from the Andrelândia and Juiz de Fora domains, Juiz de Fora, Minas Gerais

Abstract

The present study focuses on a paleobasin, in which metasedimentary rocks of the Andrelândia/Raposos Groups outcrop, along with diatexites and intrusive metagranitoids. The basin is located in the contact between the Andrelândia and Juiz de Fora Domains, subdivisions of the Occidental Terrane of the Ribeira Orogen; being also in lateral continuity with the Lima Duarte Nappe, interpreted as part of the Brasília Orogen. Rocks of both domains are affected by distinct metamorphic grades, with peak metamorphism at upper amphibolite facies in the Andrelândia Domain (above 650 °C and 7 kbars) and granulite facies (above 750 °C) in the Juiz de Fora Domain. Tourmaline-bearing metawackes occur along a significant shear zone between these two domains. These rocks are situated in the Andrelândia Domain, being characterized by a mylonitic texture with a fine grayish matrix, with clear contrast to plagioclase porphyroclasts. The metawackes locally grade into quartzites and sillimanite rich schists, also disposing lenses of calc-silicate rocks, amphibolites, and meta-ultramafic rocks. Exhalative origin minerals such as tourmaline and gahnite suggest sedimentation conditions in deep sea, associated with submarine fumaroles. Geochemical results point to a main source of intermediate composition and a magmatic arc environment context of sedimentation. U-Pb dating of the metawackes reveals a main detrital peak at ca. 678 Ma, correlated with the granitic plutons of the Socorro Nappe as the main source. Mylonitic metasedimentary rocks from the Juiz de Fora Domain were also studied for comparison. Detrital zircons of these samples reveal main peaks at ca 2079 and 1714 Ma, indicating a different provenance for these rocks compared to the metawackes of the Andrelândia Domain. Another studied lithotype is a mica schist containing green kyanite, outcropping in the Andrelândia Domain. U-Pb dating reveals a main source at ca. 2040 Ma and a secondary source at ca. 2719 Ma, correlated, respectively, with the Mantiqueira and Piedade Complexes. Garnet charnockites emerge as diatexites from the partial melting of metasedimentary rocks in the Juiz de Fora Domain. The zircon crystallization age of these charnockites at 621 ± 1.7 Ma marks the collision of these terranes, as well as the granulite peak metamorphism of the Juiz de Fora Domain. The metamorphic peak of the Andrelândia Domain is recorded by the formation of kyanite, a characteristic commonly described for rocks of the Brasília Orogen. A period of rapid tectonic exhumation is responsible for the re-equilibrium of parageneses under medium pressure/temperature conditions. A third event at 595 - 560 Ma, related to the collision with the Rio Negro Magmatic Arc, generates mylonitic texture in the rocks and contributes to the formation of a hydrated paragenesis, due to fluid percolation from the shear zones.