The Amaros and Dois Córregos plutons: Mesoarchean and Orosirian magmatism in the northern Guanhães basement inlier, Araçuaí orogen, Brazil

Abstract

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 orthogneisses of the Guanhães Complex. In the studied area, 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 TTG crust. U–Pb ICP-MS dating of zircons yielded a crystallization age of 2916 ± 19 Ma for Amaros pluton, which makes it the first Mesoarchean granite pluton delimited and detailed within the Guanhães block. Mesoarchean magmatism (ca. 2.9 Ga) similar in composition to the Amaros pluton is well known at the Porteirinha block, another basement inlier to the north of the Guanhães block, which raises questions about a connection between the two domains. The Dois Córregos pluton, firstly identified through geophysical analysis, is composed of hornblende-bearing biotite syenogranite crystallized at 2045.5 ± 24 Ma 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 continental crust, in a late-collisional stage of the Minas-Bahia orogeny, during the amalgamation of São Francisco-Congo paleocontinent.