EVOLUÇÃO GEOLÓGICA DOS GRUPOS CANASTRA E IBIÁ NA REGIÃO ENTRE COROMANDEL E GUARDA-MOR, MG

Abstract

The stratigraphic column established for the Canastra Group, in the Alto Paranaíba region in the centralportion of the Brasília Fold Belt, represents a regressive megasequence of sediments deposited on an openseacontinental platform. The following units occur from base to top: a turbiditic sequence with arenaceousand argillaceous intercalations; an arenaceous sequence containing storm beds; and a clay-rich arenaceoussequence with structures reflecting shallow marine and tidal flat environments. The Ibiá Group overlies theCanastra Group on an erosional disconformity. Its base consists of a metadiamictite of glacial origin (CubatãoFormation) while the uppermost unit (Rio Verde Formation) comprises an extensive and monotonous packageof banded calcareous phyllites. The contact between these two formations is gradational and both units havesimilar mineralogic composition. The Canastra and Ibiá Groups were affected by a single event of progressivedeformation, E1, during the Brasiliano Cycle, manifested as two distinct compressional stages. The earliestand most compressive stage, D1, is represented by thrust tectonics, associated with greenschist faciesmetamorphism. The second stage of deformation, D2, is characterized by a dominant component of pureshear in a ductile-brittle regime. When compared with other similar units in the geochronological record, thecharacteristics of the studied units show that the Ibiá Group metadiamictites are contemporaneous with theJequitaí tillite, with a probable age of deposition between 900 and 1000 Ma and the Canastra Group istherefore older than 1000 Ma.