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Jean-Paul Liégeois
Earth Sciences
Geodynamics and mineral resources
Geodynamics and mineral resources
Publication details
Kuester, D & Liégeois, J.P. 2001. ‘Sr, Nd isotopes and geochemistry of the high-grade amphibolites and gneisses from Bayuda Desert (Sudan): an early Pan-African oceanic arc assemblage and not the East Saharan ghost craton’. Precambrian Research 109: 1-23. Amsterdam : Elsevier. I.F. 3.736.
Article in a scientific Journal / Article in a Journal
Abstract
High-grade metamorphic basement of the Bayuda Desert is situated at the inferred transition between the juvenile Neoproterozoic mainly greenschist facies Arabian-Nubian Shield (ANS) and pre-Neoproterozoic mainly amphibolite facies domain of the East Saharan Ghost Craton (ESGC). New geochemical and Sr-Nd isotope data reveal that this basement constituted a Neoproterozoic oceanic convergent margin succession with limited and probably late input of old material. Within this series, garnet amphibolites and epidote-biotite gneisses have geochemical characteristics of HFSE-depleted tholeiitic basalts and low- to medium-K dacites and rhyodacites, indicating magmatism in an oceanic island arc or back-arc basin environment. This magmatism occurred at 806 ± 19 Ma (Sm-Nd 11 WR isochron), similar in age to arc magmatism in the ANS. Leucocratic gneisses, muscovite schists and garnet-biotite schists form the dominant metasedimentary rocks of the study area. They were primarily derived from two different sources: volcanogenic sediments from a Neoproterozoic island arc (TDM Nd model ages between 790 and 900 Ma) and terrigeneous sediments from an older continental source (TDM Nd model ages up to 2100 Ma). The volcanosedimentary succession was metamorphosed under amphibolite facies conditions prior to 670 Ma, probably at c.700 Ma. The high-grade metamorphism is related to a frontal collisional event that also produced muscovite-biotite gneisses with geochemical characteristics of syn-collisional peraluminous granites. Meta-igneous rocks from eastern Bayuda have Nd values of +5.2 ± 0.4 indicating a less depleted mantle source (crustal contamination is excluded) than the Gabgaba-Gebeit terrane (Nd c. +7) from the Arabo-Nubian shield. Less depleted mantle source is alos known more to the south in Gebel Moya. Lithological and structural similarities (dominantly NE striking foliation) with the Bayuda Desert succession occur in many parts of central and western Sudan. It is proposed that a Neoproterozoic oceanic convergent margin collided early (c. 700 Ma) to the NW with the East Saharan ghost craton and that the greenschist facies terranes from the Arabo-Nubian shield accreted later (640-580 Ma) during a more oblique softer collision.
Keywords: NE-Africa, Pan-African orogeny, Neoproterozoic, metamorphic rocks, isotopes, geodynamical evolution