Multi-stage formation of the Feragen ophiolite, Norway: Implication from petrology and geochemistry of peridotites and chromitites and its potential for prospecting

The ultramafic massif of Feragen, which belongs to the eastern ophiolitic belt of Norway, has abundant amounts of chromite ores. Recent studies have revealed a complex melt evolution in a supra-subduction zone (SSZ) environment. This study presents new whole-rock major element, trace element, and platinum-group element chemistry to evaluate their petrogenesis and tectonic evolution. Harzburgites have high CaO, Al₂O₃, TiO₂, MgO, and REE contents corresponding to abyssal peridotites, whereas dunites have low CaO, Al₂O₃, TiO₂, MgO, and REE contents corresponding to SSZ peridotites. The Cr# and TiO₂ of chromian spinels in the harzburgites suggest as much as about 15%–20% melting and the dunites are more depleted with > 40% melting. The harzburgites and the dunites and high-Cr chromitites represent, respectively, the products of low-degree partial melting in a back-arc setting, and the products of melt-rock interaction in a SSZ environment. The calculated ƒO₂ values for dunites and high-Cr chromitites (−0.17 – +0.23 and +2.78 – +5.65, respectively and generally above the FMQ buffer) are also consistent with the interaction between back-arc ophiolites with oxidized boninitic melts in a SSZ setting.