Origin of late precambrian intrusive carbonates, eastern desert of Egypt and Sudan: C, O and Sr isotopic evidence

Abstract

Abstract The problem of the origin of northeast African basement carbonates is approached using a regional study of C, O and Sr isotopic compositions in whole-rock samples of late Precambrian carbonate rocks of the Egyptian and Sudanese shields (ESS), from the Eastern Desert of Egypt and Sudan. The isotopic data indicate that three distinct reservoirs were available for generation of ESS intrusive carbonates: (1) sedimentary carbonates, with moderately high 87Sr/86Sr and heavy C and O; (2) depleted mantle, with low 87Sr/86Sr and light C and O; and (3) enriched mantle or lower crust, with high 87Sr/86Sr and light C and O. Isotopic data indicate that the intrusive carbonates of the North Eastern Desert were derived from reservoir (2), and a sample from the interior of Sudan was derived from reservoir (3). The origin of the remaining intrusive carbonates of the Central Eastern Desert and Sudan is best explained as mixing between remobilized sedimentary carbonates and mantle fluids, i.e. reservoirs (1) and (2). The source of the sedimentary carbonates may have been carbonate bank sediments deposited during Pan-African rifting and evolution of a passive continental margin on the north flank of the South Eastern Desert, now structurally buried under the Central Eastern Desert melange.