Zircon U-Pb-Hf evidence for subduction related crustal growth and reworking of Archaean crust within the Palaeoproterozoic Birimian terrane, West African Craton, SE Ghana

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Abstract

Zircon Lu-Hf isotopic data from granites of southern and northwestern Ghana have been used to investigate the contribution of reworked Archaean bedrock to the Birimian crust of Ghana, West African Craton. Zircon from seven localities in southern Ghana and one locality in western Ghana were analysed. Combined U-Pb and Lu-Hf isotope data suggest juvenile crustal addition between 2.3–2.1 Ga, with a short period of reworking of Archaean crust. Until now, evidence for reworking of Archaean basement during Birimian magmatism in Ghana has hinged on whole-rock Nd model-ages of the Winneba pluton, and sparse inherited zircon grains from mainly northwestern Ghana. Our data suggest that reworking of Archaean crust is greater than previously inferred, but was limited to between ∼2.14–2.13 Ga. This period of reworking of older crustal components was preceded and succeeded by juvenile crustal addition.

Coupled isotopic data suggest an eastward, mainly retreating arc system with a shorter pulse of accretion between ∼2.18–2.13 Ga and a rapid return to slab retreat during the growth of the Birimian terrane. The accretionary phase initiated melting of sub-continental lithospheric mantle and the overlying Archaean crust, generating magma with sub-chondritic Hf signatures. Subsequent slab retreat led to trench-ward movement of the magmatic activity and the mixture of juvenile and Archaean crust was replaced by uncontaminated juvenile magma. The 2.23 Ga age of the West Accra granodiorite (PK105) demonstrates the emplacement of felsic rocks during the Eoeburnean and pre-dates the suggested plume related rocks, contradicting suggested plume initiated subduction.

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Subject classification (UKÄ) – MANDATORY

  • Geochemistry
  • Earth and Related Environmental Sciences

Keywords

  • Birimian, Crustal growth, Eburnean orogeny, Zircon, Lu-Hf, U-Pb
Original languageEnglish
Pages (from-to)286–309
JournalPrecambrian Research
Volume275
Publication statusPublished - 2016 Apr
Publication categoryResearch
Peer-reviewedYes

Bibliographic note

Epublished ahead-of-print 23 January 2016

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