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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 (epsilon(Nd) (900) of -0.3 to -4.3, T(DM) model ages: 1300-1830 Ma, SrIR(900) of 0.7028-0.7055, (207)Pb/(204)Pb 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 (epsilon(Nd) (858) of 5.7-6.1, T(DM) model ages: 860-900 Ma, SrIR(858) of 0.7026-0.7028 (207)Pb/(204)Pb 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 Series is best approached by a Sm-Nd isochron age (806 +/- 19 Ma; Kuster and Liegeois [ Kuster, D., Liegeois, J.P., 2001. Sr, Nd isotopes and geochemistry of the Bayuda Desert high-grade metamorphic basement (Sudan): an early Pan-African oceanic convergent margin, not the edge of the East Saharan ghost craton? Prec. Res., 109, 1-23]). Both the Rahaba-Absol and the Kurmut terrane of the Bayuda Desert are intruded by post-collisional high-K granitoid magmatism of late Pan-African age, with no intermediate events recorded. The An Ithnein pluton that intrudes the pre-Pan-African Rahaba-Absol terrane is dated at 597 +/- 4 Ma. The isotope characteristics of this pluton (epsilon(Nd) (600) of -1.5 to 2.4, T(DM) model ages: 910-1190 Ma, SrIR(600) of 0.7011 -0.7038, (207)Pb/(204)Pb of 15.59-15.

69) and that of the Nabati pluton intruding the Kurmut terrane (&EPSILON(Nd) (600) of 0.1-4.5, T(DM) model ages: 750-1050 Ma, SrIR(600) of 0.7032-0.7036, (207)Pb/(204)Pb of 15.56-15.60) indicate a derivation from a juvenile crustal source or the mantle with limited assimilation of older crust. Post-collisional late Pan-African granite plutons at Sabaloka, south of Bayuda Desert, are distinguished into high-K and shoshonitic suites. The Banjedid high-K pluton was emplaced at 605 +/- 4 Ma, while the Babados shoshonitic pluton intruded at 591 +/- 5 Ma. Magmatic zircons from both plutons have rims with low Th/U ratios, suggesting a HT metamorphic event contemporaneous with magma emplacement. Both granitoid suites have isotopic characteristics (epsilon(Nd) (600) of -8.3 to -2.1, T(DM) model ages: 1160-1560 Ma, SrIR(600) of 0.7029-0.7069, (207)Pb/(204)Pb of 15.72-15.81) indicating the assimilation of older pre-Neoproterozoic crust. Sabaloka is thus clearly identified as a part of the Saharan Metacraton but is distinguished from the Rahaba-Absol terrane by a strong Pan-African high-grade metamorphic imprint [Kroner, A., Stern, R.J., Dawoud, A.S., Compston, W., Reischmann, T., 1987. The Pan-African continental margin in northeastern Africa: evidence from a geochronological study of granulites at Sabaloka, Sudan. Earth Planet. Sci. Lett. 85, 91-104] indicating the likely existence of a discrete Sabaloka terrane. (C) 2008 Elsevier B.V. All rights reserved.