Dating coeval mafic magmatism and ultrahigh temperature metamorphism in the Anapolis-Itaucu Complex, Central Brazil


Autoria(s): GIUSTINA, Maria Emilia Schutesky Della; PIMENTEL, Marcio Martins; FERREIRA FILHO, Cesar Fonseca; Hollanda, Maria Helena Bezerra Maia de
Contribuinte(s)

UNIVERSIDADE DE SÃO PAULO

Data(s)

20/10/2012

20/10/2012

2011

Resumo

Dating granulites has always been of great interest because they represent one of the most extreme settings of an orogen. Owing to the resilience of zircon, even in such severe environments, the link between P-T conditions and geological time is possible. However, a challenge to geochronologists is to define whether the growth of new zircon is related to pre- or post-P-T peak conditions and which processes might affect the (re) crystallization. In this context, the Anapolis-Itaucu Complex, a high-grade complex in central Brazil with ultrahigh temperature (UHT) granulites, may provide valuable information within this topic. The Anapolis-Itaucu Complex (AIC) includes ortho- and paragranulites, locally presenting UHT mineral assemblages, with igneous zircon ages varying between 760 and 650 Ma and metamorphic overgrowths dated at around 650-640 Ma. Also common in the Anapolis-Itaucu Complex are layered mafic-ultramafic complexes metamorphosed under high-grade conditions. This article presents the first geological and geochronological constraints of three of these layered complexes within the AIC, the Damolandia, Taquaral and Goianira-Trindade complexes. U-Pb (LA-MC-ICPMS, SHRIMP and ID-TIMS) zircon analyses reveal a spread of concordant ages spanning within an age interval of similar to 80 Ma with an ""upper"" intercept age of similar to 670 Ma. Under cathodoluminescence imaging, these crystals show partially preserved primary sector zoning, as well as internal textures typical of alteration during high-grade metamorphism, such as inward-moving boundaries. Zircon grains reveal homogeneous initial (176)Hf/(177)Hf values in distinct crystal-scale domains in all samples. Moreover. Hf isotopic ratios show correlation neither with U-Pb ages nor with Th/U ratios, suggesting that zircon grains crystallized during a single growth event. It is suggested, therefore, that the observed spread of concordant U-Pb ages may be related to a memory effect due to coupled dissolution-reprecipitation process during high grade metamorphism. Therefore, understanding the emplacement and metamorphism of this voluminous mafic magmatism is crucial as it may represent an additional heat source for the development of the ultrahigh temperature paragenesis recorded in the paragranulites. (C) 2010 Elsevier B.V. All rights reserved.

CNPq[477347/2007-0]

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Identificador

LITHOS, v.124, n.1/Fev, Special Issue, p.82-102, 2011

0024-4937

http://producao.usp.br/handle/BDPI/30288

10.1016/j.lithos.2010.11.004

http://dx.doi.org/10.1016/j.lithos.2010.11.004

Idioma(s)

eng

Publicador

ELSEVIER SCIENCE BV

Relação

Lithos

Direitos

restrictedAccess

Copyright ELSEVIER SCIENCE BV

Palavras-Chave #Brasilia Belt #Metamorphic zircon #UHT metamorphism #Layered mafic-ultramafic complexes #Hf-in-zircon #Coupled dissolution-reprecipitation process #HIGH-GRADE METAMORPHISM #SOUTHERN BRASILIA BELT #U-PB AGES #NEOPROTEROZOIC CRUSTAL ACCRETION #PLASMA-MASS SPECTROMETRY #SM-ND DATA #ZIRCON GEOCHRONOLOGY #TRACE-ELEMENTS #TECTONIC EVOLUTION #HF ISOTOPES #Geochemistry & Geophysics #Mineralogy
Tipo

article

original article

publishedVersion