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Mesoarchean and Orosirian Magmatism in the Northern Guanhães Basement Inlier, Araçuaí Orogen, Brazil

2022; RELX Group (Netherlands); Linguagem: Inglês

10.2139/ssrn.4255076

1556-5068

Geysianne Morais, Danilo Barbuena, Matheus Kuchenbecker,

Geological formations and processes

In this paper we present new field, geophysical, petrographic, geochemical and geochronological data from granitic rocks newly recognized at the northern Guanhães block, one of the basement inliers of the Araçuaí orogen, eastern South America. Our data allowed the identification of two granitic units, namely Amaros and Dois Córregos plutons, intrusive in the Archean ortogneisses of the Guanhães Complex. The Guanhães Complex comprises muscovite-biotite gneisses, hornblende-biotite gneisses and clinopyroxene-hornblende-biotite gneisses. These rocks have distinct chemical characteristics, which range from TTG series to Late Archean hybrid granitoids. The Amaros pluton is composed of muscovite-bearing biotite metasyenogranites. These rocks are high-K calc-alkaline, magnesian and peraluminous, and were interpreted as a product of partial melting of an older felsic crust with TTG signature. This pluton was crystallized in c. 2916 Ma (U-Pb in zircons, ICP-MS), and represents the first Mesoarchean granite body delimited and detailed within the GB. A metamorphism age of c. 531 Ma indicates the influence of the Brasiliano orogeny. Similar Mesoarchean magmatism is well known at the Porteirinha block, a basement domain north of the Guanhães block, which raises questions about a connection between the two blocks. The Dois Córregos pluton was firstly identified through geophysical analysis. It is composed of hornblende-bearing biotite metasyenogranite crystallized at c. 2045 Ma (U-Pb in zircons, ICP-MS). These rocks are alkali-calcic to alkalic, magnesian to ferroan, ranging from per- to metaluminous and were interpreted as a product of the partial melting of the thickened continental crust, in a late-collisional stage of the Minas-Bahia orogeny, during the amalgamation of São Francisco-Congo paleocontinent.