Late Precambrian crustal accretion rates in northeast Africa and Arabia

Apparent late Precambrian growth rates for continental crust in the Arabian-Nubian craton are implausibly high for simple arcaccretion models. If correct, these rates imply that some special, non uniformitarian process occurred to rapidly produce continental crust. Assuming that the dominant mechanism for continental growth is by arc magmatism, roughly 100% of global island-arc production at current rates would have had to accrete in this region from 900 to 600 Ma. One solution to this paradox is that large amounts of preexisting sialic basement have so far gone undetected and should not be included in the estimate for crustal growth during late Precambrian time. Published radiometric data indicate that older continental material makes up the eastern and western margins of the exposed shield. We interpret these and other data to suggest that the larger part of the Arabian-Nubian craton, including the platform obscured by Phanerozoic cover east and west of the exposed shield, is older continental crust. In this case, a growth rate approximately 20% of the modern global rate is required, and nonuniformitarian crustal growth is not necessary to explain late Precambrian accretion of the Arabian-Nubian craton.