Caracterização geológica-estrutural da conexão Araçuaí - São Francisco na área-tipo da Formação Rio Pardo Grande (Supergrupo Espinhaço, Minas Gerais)

Abstract

In Serra do Espinhaço Meridional, the region between the districts of Rodeador (Monjolos) and Conselheiro Mata (Diamantina), in Minas Gerais, is located in the contact between the southeastern portion of the São Francisco Craton and the western portion of the Araçuaí Orogen. The Córrego Pereira and Rio Pardo Grande formations (Conselheiro Mata Group), Duas Barras Formation (Macaúbas Group), and Sete Lagoas, Serra de Santa Helena and Lagoa do Jacaré formations (Bambuí Group) outcrop in the area, besides metabasic Neoproterozoic dikes from the Pedro Lessa Suite that cut through the Espinhaço Supergroup units. The geological and structural characterization of the area was carried out, with emphasis on the Rio Pardo Grande Formation, top unit of the Espinhaço Supergroup, li le studied until then. The Rio Pardo Grande Formation was deposited in a marine platform and is constituted, at the base, by metarritmites, metapelites and fine metarenites (Fácies Fl), with lenses of thick metarenite and metaconglomerate (facies Gsm), and metadolomites with stromatolytic structures at the top (Facies De). The registration of Facies Gsm metaconglomerates indicates the occurrence of a marine regression at the end of the deposition of the Conselheiro Mata Group, modifying the depositional model of the unit. The region's structuration is marked by expressive ductile and ruptile deformations developed during the Brasiliano Event, separated in two different deformation phases. The main features are two large NNW-SSE axis anticlinals in the eastern portion of the area, a thrust fault of N-S direction and east dip forming a regional ramp-flat context, regional wide open folds with west vergency and also considerable subvertical fractures oriented by WNW-ESE and NNW-SSE. The cinematic indicators in the region point out to mass transport form east to west.