Evidence for a complex accretionary history preceding the amalgamation of Columbia: The Rhyacian Minas-Bahia Orogen, southern São Francisco Paleocontinent, Brazil

Abstract

The Minas-Bahia orogeny juxtaposed Archean crustal fragments and Paleoproterozoic magmatic arcs to form the São Francisco-Congo Paleocontinent by the Rhyacian (ca. 2.05 Ga). Unravelling the Minas segment of the Minas-Bahia Orogenic Belt (MBO) is an important key to understanding the role of the São Francisco-Congo Paleocontinent in the construction of the Columbia Supercontinent. The Orosirian (ca. 1.9 Ga) final amalgamation of Columbia was preceded by a complex history of accretion of Archean nuclei and Proterozoic magmatic arcs. We present new whole-rock element geochemistry and isotopic (Rb-Sr, Sm-Nd) data and U-Pb ages for granitoid rocks of the main basement complexes located in the southern part of the São Francisco cratonic tip, which displays varied degrees of Neoproterozoic reworking related to the Brasiliano orogeny. Published data for the Campo Belo Complex, the Mineiro Belt and the Piedade Block are combined with the new data set to propose an integrated model for the tectonic evolution of the Minas segment of the MBO. This evolutionary model documents a complete Paleoproterozoic orogenic cycle, from subduction with terrane accretion to collision, followed by late-orogenic collapse. Subduction started diachronously between ca. 2.4 Ga and 2.2 Ga involving various Archean nuclei and Paleoproterozoic magmatic arcs that were later amalgamated during two collisional events at ca. 2.10 and 2.05 Ga. The oldest tonalite-trondhjemite-granodiorite (TTG) to sanukitoid magmatic suites transition are of Neoarchean age in the Piedade block, and of Paleoproterozoic age in the Mineiro belt and Mantiqueira complex, apparently indicating a diachronous onset of plate tectonic processes in different crustal segments. The petrogenesis, geochronology and isotopic signatures of these granitoid rocks provide important evidence towards understanding the periodicity of tectonic processes associated with the supercontinent cycle throughout Earth history.