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

Abstract

The Nyong Complex and the Yaoundé 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 Yaoundé 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 (∼Rhyacian, early-middle Paleoproterozoic) and were locally sourced from the Meso-Neoarchean Congo Shield (∼2.8 Ga); they were overprinted during the Paleoproterozoic Eburnean orogeny (∼2.2–2.0 Ga). The Yaoundé 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 (∼2.0 Ga), and Tonian-Cryogenian (∼1.0 and 0.7 Ga) sources. The meta-sedimentary rocks of both units share the Pan-African (∼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.