Provenance and tectonic evolution of the Andrelândia Group in the region between the Socorro and Guaxupé nappes, Southern Brasília and Ribeira orogens, Brazil

Abstract

Two metasedimentary successions, the Paleoproterozoic Itapira Group and the Neoproterozoic Andrelândia Group, are present in the southwestern extreme of the Southern Brasília Orogen, also affected by superposition of Ribeira Orogen tectonics. The first orogen resulted from a collision between the São Francisco paleocontinent, lower plate, and the Paranapanema paleocontinent, upper plate. The Andrelândia and Itapira groups, composed of paragneisses, quartzites, schists, and mafic/ultramafic rocks, were deformed and metamorphosed, in the studied region, under amphibolite to granulite facies conditions between 630 and 600 Ma. These metasedimentary rocks show an unconformable and tectonic contact with orthoderived basement rocks of the Amparo and Pouso Alegre complexes, considered part of the São Francisco paleocontinent. Here we present a new 1:50.000 scale geological map of the southwestern part of the Southern Brasília Orogen and six new geochronological data (LA-ICP-MS). The ages obtained in two basement samples are 2783 ± 12 Ma and 2143 ± 6 Ma. Detrital zircon analyzes in three paragneiss samples provided maximum depositional ages of ca. 1572 Ma, 1070 Ma, and 815 Ma and subordinate Archean and Paleoproterozoic ages. The maximum sedimentation ages of 1070 and 815 Ma indicate that part of the studied metasedimentary rocks is Neoproterozoic. The unconformable contact of these metasedimentary rocks with Archean and Paleoproterozoic basement rocks of the São Francisco paleocontinent justifies the interpretation that they belong to the Andrelândia Group. The crystallization age of 1716 ± 15 Ma obtained in an orthogneiss intrusive in metasedimentary rocks proves the presence of the Paleoproterozoic Itapira Complex.