Southeast Bayuda volcano-sedimentary sequences (Kurmut terrane, Sudan): juvenile island arc series within the mega-shear zone marking the eastern boundary of the Saharan Metacraton

Abstract

This study was conducted to investigate the volcano-sedimentary sequence of Kurmut terrane in southeast Bayuda Desert and its continuation east of the Nile. The sequence is situated at the inferred transition between the Neoproterozoic juvenile Arabian–Nubian Shield and the old reworked Saharan Metacraton. Lithologically, the rocks are composed of intermediate to basic metavolcanics and volcanoclastics intercalated with tuffeous material and metapelite sediments that formed in cyclic graded bedding, indicating a turbid environment in the active orogenic zone. For the first time in the study area, intraformational conglomerates with cigar-shaped volcanic clasts within the low-grade metasediments suggest a high-energy depositional environment. Minerals and textural examination of rock assemblage indicate an anticlockwise P/T condition from amphibolite facies to retrograde greenschist facies conditions in a large high strain zone of distributed deformation. Geochemical results of metavolcanics indicate derivation from different mantle sources (island arc tholeite, calc-alkaline basalt, mid-oceanic ridge, and back-arc basalt). Within this sequence, field relation and microstructural analysis clearly show the best evidence of superimposition of sinistral shear of the NNE–SSW-trending Keraf Shear Zone on the early dextral NE–SWNakasib Suture Zone. Consequently, based on lithological and structural observations with support of available geochemical data, the volcano-sedimentary sequences SE of Bayuda Desert and east of Nile are similar to their equivalent assemblage of juvenile Neoproterozoic arc lavas association of the Arabian–Nubian Shield.