Paleoproterozoic continental crust generation events at 2.15 and 2.08 Ga in the basement of the southern Brasilia Orogen, SE Brazil

Autor(es)

Cioffi, Caue Rodrigues ^{[1, 2]} ; Campos Neto, Mario da Costa ^[1] ; Moeller, Andreas ^[2] ; Rocha, Brenda Chung ^{[1, 2]}

Afiliação do(s) autor(es)

^[1] Univ Sao Paulo, Inst Geociencias, Sao Paulo, SP - Brazil

^[2] Univ Kansas, Dept Geol, Lawrence, KS 66045 - USA

• Tipo de documento: Artigo Científico
• Fonte: Precambrian Research; v. 275, p. 176-196, APR 2016.
• Citações Web of Science: 17

Resumo

New zircon U-Pb LA-ICP-MS data combined with Nd-Hf isotopes and whole-rock geochemistry provide constraints on timing and tectonic setting of Paleoproterozoic continental crust generation events in the basement of the Neoproterozoic southern Brasilia Orogen, SE Brazil. The Paleoproterozoic basement, designated as the Pouso Alegre Complex, comprises mainly metatexitic tonalitic to granodioritic orthogneisses with lenses and boudins of metamafic rocks. Minor porphyroclastic granite bodies also occur. Two well-defined crystallization ages groups were recognized at 2.14-2.15 Ga (6 samples; weighted average of 2146.7 +/- 6.6 Ma) and 2.07-2.08 Ga (5 samples; weighted average of 2078.7 +/- 6.7 Ma). Inheritance of older zircon grains is almost absent. Whole-rock Nd data show juvenile signatures with TOM ages between 2.16 and 2.37 Ga associated with positive sNcl(t) values from +0.16 to +2.85. Zircon Hf LA-ICP-MS analysis yields positive sHf(t) values from +1.9 to +8.7. Whole-rock geochemical analyses show a wide range of SiO2 contents from 52 to 76 wt% with felsic types predominating over mafic ones. The analyzed samples show high concentrations of Rb, Ba, Th, U and low Nb/La ratios, which are characteristics of subduction zone magmas and most of the samples show continental arc affinities. The geochemical signatures associated with the predominance of felsic rocks suggest a continental arc margin or an evolved accreted oceanic arc as the favored tectonic setting for the Pouso Alegre Complex. The Pouso Alegre Complex is interpreted as the southernmost and youngest recognized part of an arc complex emplaced at the southern edge of the Sao Francisco paleo-continent during the Paleoproterozoic. This part of the arc complex was deeply reworked by the collisional events related to the Neoproterozoic southern Brasilia Orogen and its cratonic counterpart is the Mineiro Belt at the southern Sao Francisco craton. The Pouso Alegre Complex and the juvenile suites of the Mineiro Belt represent a major Paleoproterozoic continental crust generation event between 2.35 and 2.08 Ga. This time period has not been recognized for extensive continental crust generation and preservation globally. However, it appears to be a major period of continental crust generation and preservation at the southern edge of the Sao Francisco paleo-continent. (C) 2016 Elsevier B.V. All rights reserved. (AU)

• Processo FAPESP: 13/13530-8 - As margens orogênicas dos blocos Paranapanema e São Francisco: de Rodinia a Gondwana
• Beneficiário: Mario da Costa Campos Neto
• Modalidade de apoio: Auxílio à Pesquisa - Regular