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

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.