Cryptic regional magmatism in the southern Saharan Metacraton at 580 Ma

Abstract

Abstract The Saharan Metacraton is largely covered by the Sahel and Sahara with only sparse bedrock exposure making it one of the most poorly studied cratons in the World. Consequently, detrital zircon geochronology is invaluable to discern the lithotectonic development of the Saharan Metacraton in the absence of outcrop. Detrital zircons from the northern Chari River, the largest river system of North-Central Africa, have ages between ~700\u202fMa and ~500\u202fMa with a small Cambrian to Ordovician (486\u202f±\u202f11\u202fMa and 422\u202f±\u202f11) population, a few Devonian to Middle Jurassic zircons (394\u202f±\u202f9\u202fMa–159\u202f±\u202f4) and a single Mesoproterozoic (959\u202f±\u202f19\u202fMa) zircon. The absence of ancient detrital zircons suggests that the crust in the vicinity of Lake Chad is primarily juvenile. A significant (~17%) proportion of zircons yielded ages of ~580\u202fMa that are broadly coeval with nappe and wrench faulting, and granulite exhumation in the Central African and Trans-Saharan orogenic belts. Moreover, we identified a gabbro from the Guera Massif of south-central Chad that yielded an in situ zircon weighted-mean 238U/206Pb age of 580\u202f±\u202f6\u202fMa. The age of the gabbro is similar to the Kekem gabbro-norite complex (576\u202f±\u202f4\u202fMa) in west Cameroon, inherited zircons from silicic rocks near Lake Fitri and Lake Chad, and the detrital zircons from the Chari River. Our results unequivocally demonstrate that there was magmatism at ~580\u202fMa and that it was contemporaneous with deformation along the Tchollire-Banyo and Central Cameroon shear zones indicating there was a major regional tectonomagmatic episode at that time. We suggest the mafic magmatism was related to post-orogenic mantle upwelling that may have been responsible for or contributed to lithospheric delamination of the southern Saharan Metacraton.