Zircon geochronology and Sr, Nd, Pb isotope geochemistry of granitoids from Bayuda Desert and Sabaloka (Sudan): Evidence for a Bayudian event (920–900 Ma) preceding the Pan-African orogenic cycle (860–590 Ma) at the eastern boundary of the Saharan Metacraton

• Published in: Precambrian research 2008-06, Vol.164 (1), p.16-39
• Main Authors: Küster, Dirk, Liégeois, Jean-Paul, Matukov, Dmitry, Sergeev, Sergei, Lucassen, Friedrich
• Format: Article
• Language: English
• Subjects: Bayudian; Granitoids; Neoproterozoic; Pan-African; Saharan Metacraton; Zircon geochronology
• ISSN: 0301-9268; 1872-7433
• DOI: 10.1016/j.precamres.2008.03.003

Results of zircon geochronology and Sr, Nd and Pb isotope investigations carried out on granitoid rocks from the boundary of the Saharan Metacraton with the Arabian–Nubian Shield (ANS) reveal a protracted, partly pre-Pan-African geodynamic evolution and the existence of crustal terranes of different ancestries. (Meta)granitoids and gneisses in north-central Bayuda Desert record a 920–900 Ma orogenic event, hitherto unrecognized in northeastern Africa. This early Neoproterozoic Bayudian event is restricted to a pre-Pan-African crustal terrane which appears only slightly affected by Pan-African tectogenesis and deformation, named here the Rahaba–Absol terrane. Within this terrane, amphibolite-facies metamorphism occurred at 921 ± 10 Ma in the El Melagi muscovite–biotite gneiss of the Rahaba Series, probably during a collisional phase; followed by the intrusion of the Absol medium-K granite–granodiorite pluton discordantly emplaced at 900 ± 9 Ma into high-grade schists and amphibolites of the metavolcanosedimentary Absol Series. Nd T DM model ages (2040–2430 Ma) and ages of rounded zircon cores (1060, 1980, 2540 and 2675 Ma) of the El Melagi gneiss indicate a predominantly late Archaean to Palaeoproterozoic source region and suggest a latest Mesoproterozoic to early Neoproterozoic depositional age of its pelitic precursor sediment. The post-collisional Absol pluton has isotope characteristics ( ɛ Nd 900 of −0.3 to −4.3, T DM model ages: 1300–1830 Ma, SrIR 900 of 0.7028–0.7055, 207Pb/ 204Pb of 15.66–15.81) indicating assimilation of old pre-Neoproterozoic crust. The Rahaba–Absol terrane is part of the Saharan Metacraton and is in tectonic contact with the high-grade metamorphic Kurmut terrane of eastern Bayuda Desert. The Kurmut terrane has juvenile Neoproterozoic isotope characteristics, its granitoids record only Pan-African orogenic events and it is therefore considered a part of the Arabian–Nubian Shield. Within the Kurmut terrane the Dam Et Tor medium-K epidote–biotite gneiss gave a concordant zircon age of 858 ± 9 Ma, interpreted as the crystallization age of the volcanic/subvolcanic precursor of the gneiss. Isotopic data of the Dam Et Tor gneiss ( ɛ Nd 858 of 5.7–6.1, T DM model ages: 860–900 Ma, SrIR 858 of 0.7026–0.7028, 207Pb/ 204Pb of 15.46) indicate a depleted mantle source and an oceanic arc magmatic environment. The age of the amphibolite-facies metamorphism and deformation of the Dam Et Tor gneiss and its enclosing metavolcanosedimentary Kurmut