How diverse is the source? Age, provenance, reworking, and overprint of Precambrian meta-sedimentary rocks of West Gondwana, Cameroon, from zircon U-Pb geochronology

The Nyong Complex and the Yaounde Group represent two crustal sequences of West Gondwana in Cameroon. We use U-Pb zircon geochronology on meta-sedimentary rocks to analyze their depositional age, provenance, and age of the high-grade metamorphic overprint. Due to the undoubtedly Precambrian age of these rocks, we also pursue questions regarding the veiling of the provenance signal by subsequent overprints, the diversity of the sources, and the role of crustal reworking in such an old setting. Although both the Nyong and the Yaounde meta-sedimentary rocks were strongly affected by the Pan-African orogeny, Discordia analysis and the evaluation of remnant concordant zircons allow addressing these classic provenance questions with the LA-ICP-MS U-Pb zircon technique. We show that the Nyong Complex meta-sedimentary rocks likely have a <2.4 and > 2.2 Ga depositional age (similar to Rhyacian, early-middle Paleoproterozoic) and were locally sourced from the Meso-Neoarchean Congo Shield (similar to 2.8 Ga); they were overprinted during the Paleoproterozoic Eburnean orogeny (similar to 2.2-2.0 Ga). The Yaounde Group meta-sedimentary rocks likely have a <0.7 Ga depositional age (Cryogenian, middle Neoproterozoic); they lack a major Archean source, and have distinct, likely locally-sourced Eburnean (similar to 2.0 Ga), and Tonian-Cryogenian (similar to 1.0 and 0.7 Ga) sources. The meta-sedimentary rocks of both units share the Pan-African (similar to 0.6 Ga) orogenic overprint. Our study highlights the limited source diversity of these old basin deposits with a provenance from the few existing crustal masses.

Automated summary

The Nyong Complex and the Yaounde Group in Cameroon represent two different crustal sequences with distinct depositional ages and sources, influenced by the Pan-African orogeny. The Nyong Complex likely sourced from the Meso-Neoarchean Congo Shield around 2.8 Ga, while the Yaounde Group lacks a major Archean source and has sources from the Eburnean and Tonian-Cryogenian events. Both units share a Pan-African orogenic overprint, highlighting the limited source diversity of these old basin deposits.