Petrogenetic evolution of I-type granitoids in the Gouna region, Northern Cameroon: Geochemical evidence for subduction-related to post-collisional magmatism during the Pan-African orogeny

Abstract

The Gouna region, located in the northern part of the Pan-African belt in Cameroon, comprises a diverse suite of granitoids, including amphibole granites, amphibole–biotite granites, biotite granites, biotite–muscovite granites, and muscovite-bearing leucogranites. Deciphering their magmatic sources and tectonic evolution is key to understanding the geodynamic framework of the Pan-African Belt, which records the transition from subduction-related to post-collisional regimes during the Neoproterozoic.

This study integrates petrographic investigations of 25 thin sections, whole-rock geochemical analyses of 13 representative samples (11 granites and 2 quartz diorites), and new Sr–Nd isotopic data to constrain the petrogenetic evolution of the Gouna granitoids. The rocks are metaluminous, calc-alkaline, and magnesian (SiO₂ = 67.55–73.15 wt%; K₂O/Na₂O < 1), characteristic of I-type granites emplaced under hydrous, oxidizing conditions. Isotopic compositions (⁸⁷Sr/⁸⁶Srᵢ = 0.7068–0.7072; εNd (540 Ma) = −4.8 to −6.2) suggest hybrid magma sources derived from a metasomatized enriched mantle with variable crustal assimilation.

Amphibole granites display weak REE fractionation ((La/Yb)_n = 0.64–1.68) and pronounced negative Eu anomalies (Eu/Eu* = 0.29–0.45), whereas muscovite-bearing leucogranites are highly fractionated ((La/Yb)_n = 17.30–33.71). Primitive mantle–normalized patterns show consistent negative anomalies in Nb, Ta, Ti, Pb, Sr, Y, and Hf, and enrichment in LILEs relative to HFSEs, reflecting a subduction-modified source.

The geochemical and isotopic data collectively record a polyphase magmatic evolution, marking the transition from arc-related mantle magmatism to syn- and post-collisional anatexis (600–540 Ma), and highlight progressive mantle–crust interaction during the Pan-African orogeny.