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Complex, 3D strain patterns in a synkinematic tonalite batholith from the Aracuai Neoproterozoic orogen (Eastern Brazil): Evidence from combined magnetic and isotopic chronology studies

Texto completo
Mondou, Mathieu [1, 2, 3] ; Egydio-Silva, Marcos [1] ; Vauchez, Alain [2, 3] ; Raposo, Maria Irene B. [1] ; Bruguier, Olivier [2, 3] ; Oliveira, Alexandra Fernandes [1]
Número total de Autores: 6
Afiliação do(s) autor(es):
[1] Univ Sao Paulo, Inst Geociencias, BR-05508080 Sao Paulo - Brazil
[2] CNRS, F-34095 Montpellier 05 - France
[3] Univ Montpellier 2, F-34095 Montpellier 05 - France
Número total de Afiliações: 3
Tipo de documento: Artigo Científico
Fonte: JOURNAL OF STRUCTURAL GEOLOGY; v. 39, p. 158-179, JUN 2012.
Citações Web of Science: 16

This work combines structural and geochronological data to improve our understanding of the mechanical behaviour of continental crust involving large amount of magma or partially melted material in an abnormally hot collisional belt. We performed a magnetic and geochronological (U/Pb) study on a huge tonalitic batholith from the Neoproterozoic Aracual belt of East Brazil to determine the strain distribution through space and time. Anisotropy of magnetic susceptibility, combined with rock magnetism investigations, supports that the magnetic fabric is a good proxy of the structural fabric. Field measurements together with the magnetic fabrics highlight the presence in the batholith of four domains characterized by contrasted magmatic flow patterns. The western part is characterized by a gently dipping, orogen-parallel (similar to NS) magmatic foliation that bears down-dip lineations, in agreement with westward thrusting onto the Sao Francisco craton. Eastward, the magmatic foliation progressively turns sub-vertical with a lineation that flips from sub-horizontal to sub-vertical over short distances. This latter domain involves an elongated corridor in which the magmatic foliation is sub-horizontal and bears an orogen-parallel lineation. Finally the fourth, narrow domain displays sub-horizontal lineations on a sub-vertical magmatic foliation oblique (similar to N150 degrees E) to the trend of the belt. U/Pb dating of zircons from the various domains revealed homogeneity in age for all samples. This, together with the lack of solid-state deformation suggests that: 1) the whole batholith emplaced during a magmatic event at similar to 580 Ma, 2) the deformation occurred before complete solidification. and 3) the various fabrics are roughly contemporaneous. The complex structural pattern mapped in the studied tonalitic batholith suggests a 3D deformation of a slowly cooling, large magmatic body and its country rock. We suggest that the development of the observed 3D flow field was promoted by the low viscosity of the middle crust that turned gravitational force as an active tectonic force combining with the East-West convergence between the Sao Francisco and Congo cratons. (C) 2012 Elsevier Ltd. All rights reserved. (AU)

Processo FAPESP: 05/56372-7 - Reologia da crosta continental, fusão parcial e magmatismo granítico: a Faixa Ribeira/Araçuaí (Leste/Sudeste do Brasil). Um equivalente da "Astenosfera crustal" do Sul do Tibete e dos Andes Centrais?
Beneficiário:Marcos Egydio da Silva
Linha de fomento: Auxílio à Pesquisa - Regular
Processo FAPESP: 10/50475-7 - Origem e evolucao petrogenetica e estrutural do granito carlos chagas:faixa aracuai (leste do brasil).
Beneficiário:Marcos Egydio da Silva
Linha de fomento: Auxílio à Pesquisa - Regular