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Geochemistry and age of mafic rocks from the Votuverava Group, southern Ribeira Belt, Brazil: Evidence for 1490 Ma oceanic back-arc magmatism

Texto completo
Autor(es):
Campanha, G. A. C. [1] ; Faleiros, F. M. [1] ; Basei, M. A. S. [1] ; Tassinari, C. C. G. [1] ; Nutman, A. P. [2, 3, 4] ; Vasconcelos, P. M. [5]
Número total de Autores: 6
Afiliação do(s) autor(es):
[1] Univ Sao Paulo, Inst Geociencias, BR-05508080 Sao Paulo, SP - Brazil
[2] Australian Natl Univ, Res Sch Earth Sci, Canberra, ACT 0200 - Australia
[3] Univ Wollongong, Sch Earth & Environm Sci, GeoQuEST Res Ctr, Wollongong, NSW 2522 - Australia
[4] Chinese Acad Geol Sci, Inst Geol, Beijing SHRIMP Ctr, Beijing - Peoples R China
[5] Univ Queensland, Dept Earth Sci, Brisbane, Qld 4072 - Australia
Número total de Afiliações: 5
Tipo de documento: Artigo Científico
Fonte: Precambrian Research; v. 266, p. 530-550, SEP 2015.
Citações Web of Science: 14
Resumo

This paper presents new SHRIMP U-Pb zircon and Ar-40-Ar-39 hornblende ages as well as elemental and Sr-Nd isotopic data for greenschist to amphibolite fades meta-mafic rocks from the Votuverava Group (Ribeira Belt, Brazil). These mafic rocks appear to be mostly subvolcanic and volcanic rocks and, in part, intrusions coeval with the host sedimentary succession. Magmatic zircons have a U-Pb age of 1488 +/- 4 Ma. An Ar-40-Ar-39 hornblende age of 1390 +/- 20 Ma suggests cooling after a thermal event. The mafic rocks have chemical compositions of basalt and basaltic andesite (SiO2 of 45-55 wt.%) of the tholeiitic series. Chemical data indicate the coexistence of rocks with BABB and E-MORB signatures. BABB-like rocks with a Ti/V of 9-20 show depletion in HFSE relative to MORB values and slightly fractionated REE patterns (La-cn/Yb-cn of 0.8-1.8), while those with a Ti/V of 22-30 have HFSE contents similar to MORS and slightly more fractionated REE patterns (La-cn/Yb-cn of 1.1-2.8). E-MORB-like rocks display a Ti/V of 27-41 and moderately fractionated REE patterns (La-cn/Yb-cn of 3.6-5.3). The epsilon(Nd)(t) values ranged from -3.02 to +3.55. Whole rock Sm-Nd isotopic data yielded a regression with a slope of 1225 +/- 68 Ma, which can be interpreted as a mixing line of no age significance that is related to different source components of the metabasic rocks. Elemental and Nd isotopic signatures suggest that the Votuverava metabasites originated from a MORB-type mantle source heterogeneously metasomatized by subduction processes. The data are consistent with magmatic activity in a back-arc basin environment. The 1490 Ma mafic magmatism is associated with a 500-km-long and 60-km-wide Calymmian belt interpreted as an accretionary orogen. Available thermochronological data suggest that this accretionary orogen could have evolved into a collisional orogen in the period 1280-1100 Ma, possibly related to the assembly of Rodinia. During the Brasiliano-Pan African cycle (650-550 Ma), related to amalgamation of West Gondwana, this Calymmian belt represented by the Votuverava Group was dispersed as an exotic terrane along the Ribeira Belt. (C) 2015 Elsevier B.V. All rights reserved. (AU)

Processo FAPESP: 06/01327-0 - Caracterização metamórfica, estrutural e geocronológica de terrenos pré-cambrianos no Sul do Estado de São Paulo
Beneficiário:Ginaldo Ademar da Cruz Campanha
Linha de fomento: Auxílio à Pesquisa - Regular
Processo FAPESP: 01/13457-1 - Caracterização isotópica de rochas dos subgrupos Ribeira e Lajeado na região de Iporanga, SP
Beneficiário:Ginaldo Ademar da Cruz Campanha
Linha de fomento: Auxílio à Pesquisa - Regular
Processo FAPESP: 96/05648-1 - Análise da cinemática, nível crustal e fluxos de fluidos das zonas de cisalhamento da porção meridional da Faixa Apiaí
Beneficiário:Ginaldo Ademar da Cruz Campanha
Linha de fomento: Auxílio à Pesquisa - Regular