New U–Pb zircon ages of Nyong Complex meta‐plutonites: Implications for the Eburnean/Trans‐Amazonian Orogeny in southwestern Cameroon (Central Africa)

New LA–ICP–MS U–Pb zircon ages from the Nyong Complex of southwestern Cameroon—a part of the West Central African Fold Belt—trace Late Mesoarchean (∼2,850 Ma), Middle Palaeoproterozoic (∼2,080 Ma), and Neoproterozoic (∼605 Ma) events: Two meta‐syenites and the protolith of an amphibolite are Late Mesoarchean; two meta‐granodiorites are Middle Palaeoproterozoic; the amphibolite may have recrystallized in the Middle Palaeoproterozoic; all rocks are overprinted by the Neoproterozoic event. Integration with published data shows that our amphibolite sample has one of the oldest amphibolite‐protolith ages (∼2,810 Ma) reported so far. It shares the Middle Palaeoproterozoic metamorphism/recrystallization with other, previously dated amphibolites. An earlier reported metamorphic zircon age (∼2,090 Ma) from eclogite is somewhat older than the regional Middle Palaeoproterozoic metamorphism/recrystallization ages (∼2,040 Ma) reported from amphibolites. Thus, the eclogite–amphibolite ages may date an exhumation process. A published charnockite age, interpreted as an Early Mesoarchean crystallization age, is older than the Late Mesoarchean meta‐syenite and amphibolite‐protolith dates; its Middle Palaeoproterozoic metamorphism/recrystallization age, however, is identical with the meta‐granodiorites and amphibolites. The Neoproterozoic ages demonstrate the regional overprint of the Nyong Complex during this period. Integration of the Nyong Complex ages with published ones from the entire West Central African Fold Belt, and comparison with those from West Africa and South America, support their common origin from the Palaeoproterozoic collision between the Archean Congo and São Francisco shields.


| SAMPLING AND ANALYTICAL METHODS
Our sampling strategy aimed for plutonic and metamorphic lithologies from the Nyong Complex that were not fully covered in previous studies, and to achieve a better understanding of the regional extent of the Eburnean/Trans-Amazonian Orogeny in Cameroon. To this end, we retrieved zircon grains from two meta-syenites (OS7 and OW2B), one amphibolite (OS19), and two meta-granodiorites (OW326, OW376) ( Figure 2 and Table 1). We fragmented the rock samples using the high-voltage discharge SELFRAG facility at the TU Bergakademie Freiberg. Prior to mounting in epoxy, zircon concentrates were enriched with a Frantz magnetic separator, shaking tables, wet and dry sieving, wet panning, heavy liquids, and handpicking. Cathodoluminescence (CL) images were used to study the zircon textures that add to the interpretation of their geologic history (e.g., Corfu, Hanchar, Hoskin, & Kinny, 2003), and to avoid placing the laser ablation (LA) pits into possible multiple-age domains (e.g., core-rim boundaries) or inclusions. The inductively coupled plasma (ICP) mass spectrometry (MS) was performed at the Geochronology Laboratory of the Senckenberg Naturhistorische Sammlungen, Dresden,

Germany. The laboratory uses a New Wave UP-193 Excimer Laser
System coupled to a Thermo-Scientific Element 2 XR sector field LA-ICP-MS to collect U, Th, and Pb measurements for zircon grains.
The data are not common Pb-corrected, and were generated using previously outlined protocols (Frei & Gerdes, 2009;Linnemann et al., 2011), with the caveat that data was processed using Iolite  Table S1 provides the instrument settings of the geochronologic laboratory). We used Isoplot (Ludwig, 2008) to calculate, depending on context, the geologically most meaningful ages; these are either Concordia, weighted mean, or upper and lower intercept ages.

| SAMPLE LITHOLOGY
The meta-syenites show a metamorphic foliation and display a greyish-pink colour from outcrop-to hand-specimen scale ( Figure 3a).

| Meta-syenites
We dated two meta-syenites. Sample OS7 displays a broad scatter of discordant analyses, indicating both Pb loss and common Pb contamination. Six analyses span a Discordia with an upper intercept (UI) at 2,883 ± 74 Ma and a lower intercept (LI) at 603 ± 110 Ma (2σ; MSWD = 14; Figure 4a). Although the high MSWD indicate nonanalytical scatter, for example, the presence of common Pb also in these analyses, we interpret the UI to approximate the crystallization  It is likely that there is a relict Palaeoproterozoic event.

Lambert-Smith et al. (2015) described monzodiorites with Palaeo-to
Mesoarchean U-Pb zircon crystallization ages (3,380-3,000 Ma), among the oldest crustal pieces recognized so far in West Africa.
Although the definition of the onset and termination of the Eburnean/ Trans-Amazonian Orogeny is, in our opinion, more arbitrary than in the WCAFB, a grossly similar evolution is displayed in the South American fold belts (2,288-1,962 Ma, median of 95 dates = 2,109 + 18/ −21 Ma), and the West African fold belts (2,290-1,850 Ma, median of 294 dates = 2,120 + 7/−9 Ma); this difficulty in the determination of the boundaries of the age ranges reflects the greater amount and variability of the available dates ( Figure 7 and Table S3). The compilation may also hint to an asynchrony of the Eburnean/Trans-Amazonian Orogeny, having been earlier in the West African and South American fold belts than the WCAFB (Figure 7). These Palaeoproterozoic oro-

PEER REVIEW
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DATA AVAILABILITY STATEMENT
The data that supports the findings of this study are available in the supplementary material of this article.