Geochemical Evolution and Tectonic Setting of Neoproterozoic Serpentinites from the Bou Azzer Ophiolite, Morocco: Evidence for Subduction-Related Mantle Wedge Processes

The Bou Azzer inlier of the Central Anti-Atlas (Morocco) exposes a relic of a Neopro-terozoic ophiolitic complex, in which serpentinites constitute a volumetrically im-portant constituent of the mantle sequence. These serpentinites form WNW-ESE-trending discontinuous bands and lenses that are emplaced as steeply dip-ping sheets along major thrust faults. Field mapping, drill-core observations, petrog-raphy, SEM, XRD, and geochemical analyses collectively suggest corroboration that complete serpentinization has erased primary olivine and pyroxene, save relic bastite textures and chromian spinel cores that carry crucial information on the mantle source. The serpentinites exhibit textures ranging from well-preserved mesh and bas-tite pseudomorphic textures to strongly foliated and talc-carbonate–altered ones, par-ticularly along shear zones, indicating multistage serpentinization under evolving de-formation conditions. Mineral assemblages are dominated by antigorite ± chrysotile ± lizardite, with secondary magnetite, talc, and carbonates formed during late-stage fluid–rock interaction. Bulk-rock major and trace element geochemistry is typical of depleted mantle, with low Al₂O₃, CaO, and TiO₂, high Mg# (0.81–0.85), and elevated Cr and Ni compared to primitive mantle, consistent with a harzburgitic mantle residuum produced by high degrees of partial melting. Petrographical and geochemical analyses collectively suggest that the Bou Azzer serpentinites are essentially derived from harzburgitic and dunitic, and minor wehrlites and lherzolite protoliths. These features highlight significant mantle heterogeneity beneath Bou Azzer, shaped by variable de-grees of melt extraction and subsequent metasomatism. Chromite chemistry (Cr# = 0.50–0.67, Mg# = 0.43–0.77, TiO₂ ≤ 0.18 wt.%) and Cr–Al–Fe³⁺ compositional plots indi-cate a supra-subduction zone (SSZ) tectonic setting. All of these results together rein-force the interpretation of the Bou Azzer serpentinites as isolated remnants of a Pan-African SSZ-type mantle wedge that was hydrated, carbonated, and deformed during obduction and later transpression at the West African Craton margin.