U-Pb SHRIMP and Sm-Nd geochronology of granite-gneiss complexes and implications for the evolution of the Central Brazil Archean Terrain

C.L. Queiroz, H. Jost, L.C. Da Silva, Nicholas Mcnaughton

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    Abstract

    The paper is a first attempt to unravel the previous termArcheannext term multi-stage metaplutonic assemblage of the Meso/Neoarchean terrane of the State of Goiás, previous termCentral Brazil,next term by means of the previous termU–Pb SHRIMPnext term zircon and previous termSm–Ndnext term techniques. Two stages of granitic plutonism, spanning ca. 140 m.y., were precisely established for the accretion of the previous termgneissnext term protoliths. The earliest stage embraces tonalitic to granodioritic and minor granitic orthogneisses with previous termNdnext term juvenile signature, emplaced from ca. 2845 to ca. 2785 Ma, interpreted as the roots of an early arc. Inherited zircon xenocrysts and previous termNdnext term isotopic data indicate that the juvenile magmas underwent contamination from a sialic crust as old as 3.3 Ga, from which there are, so far, no recognizable exposures. The second stage comprises granodioritic to granitic previous termgneissesnext term and lasted from ca. 2711 to 2707 Ma. Based on their previous termNdnext term isotopic signatures and on inherited zircon crystals, their protoliths are interpreted as dominantly crustal-derived. The previous termSHRIMPnext term data from zircon crystals did not depict a Paleoproterozoic overprinting on the previous termArchean gneisses,next term which is due to geological processes with prevailing temperatures below the isotopic stability of the previous termU/Pb/next termTh system in the mineral. These processes comprise crustal extension and intrusion of a mafic dike swarm at ca. 2.3 Ga, followed by low grade events mostly related to shear zones between ca. 2.15 and 2.0 Ga. The study also revealed the extent of the Pan- African tectono-thermal overprinting on the previous termArcheannext term orthogneisses. Most of the zircon populations show morphological evidence of metamorphic peripheral recrystallization dated between ca. 750 and 550 Ma. One of the banded previous termgneissesnext term with a crystallization age of ca. 2700 Ma (2σ) has a more previous termcomplexnext term zircon population including magmatic new grains, which yielded a precise 206Pb/238U crystallization age of 590 ± 10 Ma (2σ). These new grains are interpreted to have grown in anatectic veins injected within strongly sheared previous termgneiss.next termThe data characterize a widespread Pan-African-aged metamorphic overprinting, culminating with localized anatexis of the previous termArcheannext term orthogneisses.
    Original languageEnglish
    Pages (from-to)100-124
    JournalJournal of South American Earth Sciences
    Volume26
    Issue number1
    DOIs
    Publication statusPublished - 2008

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