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

摘要: Abstract Results of zircon geochronology and Sr, Nd Pb isotope investigations carried out on granitoid rocks from the boundary Saharan Metacraton with Arabian–Nubian Shield (ANS) reveal a protracted, partly pre-Pan-African geodynamic evolution existence crustal terranes different ancestries. (Meta)granitoids gneisses in north-central Bayuda Desert record 920–900 Ma orogenic event, hitherto unrecognized northeastern Africa. This early Neoproterozoic Bayudian event is restricted to terrane which appears only slightly affected by Pan-African tectogenesis deformation, named here Rahaba–Absol terrane. Within this terrane, amphibolite-facies metamorphism occurred at 921 ± 10 Ma El Melagi muscovite–biotite gneiss Rahaba Series, probably during collisional phase; followed intrusion Absol medium-K granite–granodiorite pluton discordantly emplaced 900 ± 9 Ma into high-grade schists amphibolites metavolcanosedimentary Series. TDM model ages (2040–2430 Ma) rounded cores (1060, 1980, 2540 2675 Ma) indicate predominantly late Archaean Palaeoproterozoic source region suggest latest Mesoproterozoic depositional age its pelitic precursor sediment. The post-collisional has characteristics (ɛNd 900 −0.3 −4.3, ages: 1300–1830 Ma, SrIR900 0.7028–0.7055, 207Pb/204Pb 15.66–15.81) indicating assimilation old pre-Neoproterozoic crust. part tectonic contact metamorphic Kurmut eastern Desert. juvenile characteristics, granitoids events it therefore considered Shield. Dam Et Tor epidote–biotite gave concordant 858 ± 9 Ma, interpreted as crystallization volcanic/subvolcanic gneiss. Isotopic data 858 5.7–6.1, 860–900 Ma, SrIR858 0.7026–0.7028, 15.46) depleted mantle an oceanic arc magmatic environment. deformation enclosing Series best approached Sm–Nd isochron (806 ± 19 Ma; Kuster Liegeois [Kuster, D., Liegeois, J.P., 2001. isotopes geochemistry basement (Sudan): convergent margin, not edge East ghost craton? Prec. Res., 109, 1–23]). Both are intruded high-K magmatism age, no intermediate recorded. An Ithnein that intrudes dated 597 ± 4 Ma. 600 −1.5 2.4, 910–1190 Ma, SrIR600 0.7011–0.7038, 15.59–15.69) Nabati intruding 0.1–4.5, 750–1050 Ma, 0.7032–0.7036, 15.56–15.60) derivation or limited older Post-collisional granite plutons Sabaloka, south Desert, distinguished shoshonitic suites. Banjedid was 605 ± 4 Ma, while Babados 591 ± 5 Ma. Magmatic zircons both have rims low Th/U ratios, suggesting HT contemporaneous magma emplacement. suites isotopic −8.3 −2.1, 1160–1560 Ma, 0.7029–0.7069, 15.72–15.81) Sabaloka thus clearly identified but strong imprint [Kroner, A., Stern, R.J., Dawoud, A.S., Compston, W., Reischmann, T., 1987. continental margin Africa: evidence geochronological study granulites Sudan. Earth Planet. Sci. Lett. 85, 91–104] likely discrete