Cryptic regional magmatism in the southern Saharan Metacraton at 580 Ma

• Published in: Precambrian research Vol. 332; p. 105398
• Main Authors: Shellnutt, J. Gregory, Yeh, Meng-Wan, Pham, Ngoc Ha T., Lee, Tung-Yi
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.09.2019
• Subjects: Chad; Chari River; Detrital zircon geochronology; Guéra Massif; Neoproterozoic; Saharan Metacraton; Guéra Massif; Chad; Chari River; Saharan Metacraton; Detrital zircon geochronology; Neoproterozoic
• ISSN: 0301-9268; 1872-7433
• DOI: 10.1016/j.precamres.2019.105398

[Display omitted] •Chari River detrital zircon ages range from 959 ± 19 Ma to 159 ± 4 Ma.•There is an abundance of zircon ages from 700 Ma to 500 Ma with at peak at ~590 Ma.•The Guéra Massif gabbro yielded a weighted-mean 2•38U/206Pb age of 580 ± 6 Ma.•Magmatism accompanied deformation along the Tcholliré-Banyo and Central Cameroon shear zone.•There was a major tectonothermal event at ~580 Ma within the Saharan Metacraton. 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 Ma and ~500 Ma with a small Cambrian to Ordovician (486 ± 11 Ma and 422 ± 11) population, a few Devonian to Middle Jurassic zircons (394 ± 9 Ma–159 ± 4) and a single Mesoproterozoic (959 ± 19 Ma) 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 Ma 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 Guéra Massif of south-central Chad that yielded an in situ zircon weighted-mean 238U/206Pb age of 580 ± 6 Ma. The age of the gabbro is similar to the Kekem gabbro-norite complex (576 ± 4 Ma) 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 Ma and that it was contemporaneous with deformation along the Tcholliré-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.