The Bom Repouso Agpaitic Suite (MG, Brazil): geology, geochemistry and geochronology

The Bom Repouso Agpaitic Suite (BRAS; 76.5–78.4 Ma, 40Ar/39Ar) is situated in a limited area to the south of Minas Gerais State, SE Brazil. The outcrop is ~1 km² in area and is crescent shaped, with two small satellite plugs. The BRAS is represented by felsic, fine-grained rocks that contain albite, K-feldspar, nepheline and aegirine/aegirine–augite. In addition, the principal accessory minerals include arfvedsonite, aenigmatite, sodalite and eudialyte, along with schizolite, astrophyllite, cryolite, niobophyllite, catapleiite and several other less abundant minerals. The rocks are agpaitic phonolites, characterized by an alkalinity index range of 0.99–1.20, with the presence of Na–Ti–Zr silicates and a high content of incompatible elements, especially Zr and rare earth elements. They are also highly depleted in Sr, Ba, MgO and compatible elements. These rocks are intrusive in the Precambrian migmatitic gneisses of the Socorro Nappe, situated between the Poços de Caldas–Cabo Frio Lineament and Northen Sector from the Serra do Mar Province. The displayed characteristics suggest a greater affinity with the magmatism from the alkaline province of the Poços de Caldas– Cabo Frio Lineament, exhibiting notable similarities with the agpaitic rocks from Poços de Caldas and other occurrences in the province.