Comparação da evolução geológica entre as rochas metassedimentares dos grupos Vazante e Canastra no entorno à Vazante, MG: litoestratigrafia, estrutura e isótopos de samário-neodímio(Sm-Nd) e estrôncio (Sr)

• Autor(a) principal: Carvalho, Manuela de Oliveira
• Data de Publicação: 2015
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UERJ
• Texto Completo: http://www.bdtd.uerj.br/handle/1/7149
• topic: Canastra Group; Vazante group; Brasília Belt; Radiogenic isotopes; Grupo Canastra; Grupo Vazante; Faixa Brasília; Isótopos Radiogênicos; CNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIA

In the context of Southern Brasília Belt in the region of Vazante (NW of Minas Gerais) occurs two thrust-faults that consists of metasedimentary rocks from the Canastra and Vazante groups, in an area of approximately 400 km2. In this region are the largest zincnonsulfide deposit of the world, the mine of Vazante. The lower thrust-fault consists, from the base to top, of the formations Serra do Garrote (slates and carbonaceous phyllite), Serra do Poço Verde (slate, marls and dolomites), Morro do Calcário (stromatolite metadolomite) and Serra da Lapa (slates with subordinated dolomites), belonging to Vazante Group. The carbonaceous slates and phyllite with interbedded quartzite from the Paracatu Formation, Canastra Group, represents the higher thrust-fault. The conditions of metamorphism that affected these units reached the lower green schist facies (pre-biotite zone). The Brazilian Cycle resulted in complex structures with at least four superimposed phases of compressive deformation. The first two phases (D1, D2) are ductile related with the tectonic setting of thrust and nappes, while the third and fourth (D3 and D4) are brittle-ductile. The D1 phase was responsible for a slaty cleavage S1 subparallel to the primary layering (So), with strike NE-SW and low to high dips to NW and subordinate to SE. The phase D2, is responsible for isoclines folds and a S2 spaced cleavage, that may or not be parallel to the primary layering (S1 // So // S2 or S1 // So oblique to S2), with strike NE-SW and moderate to high dips predominantly to NW. The phase D3 is responsible for open folds and kinks with a spaced crenulation cleavage S3 to NE-SW with moderate to high dips and predominant axis to NW. The phase D4 is responsible for open folds with a spaced crenulation cleavage S4 to NW-SE with moderate to high dips and axis to NE and SW. The Sm-Nd model ages show TDM distributions between 1.47 and 2.34 Ga for the Vazante Group rocks, with younger ages belonging to the Serra da Lapa Formation and the older ones to the Serra do Garrote Formation. The Canastra Group shows model ages between 1.47 to 2.47 Ga. These values of Model Ages (TDM) indicate that most of the sedimentary sources are Paleoproterozoic, probably from the São Francisco Craton basement, with a small participation of younger sources of Middle Neoproterozoic.