Primary versus secondary high-Cr signatures in ophiolitic chromitite: grain-scale evidence from the Kop ophiolite, NE Türkiye

Fresh chromite from the Kop chromitites in northeastern Türkiye exhibits Cr# values of 0.73–0.84 and TiO2 content of 0.03–0.26 wt%. BSE imaging, electron-probe analyses, and WDS element maps distinguish relatively preserved interiors from fracture-related replacement domains and secondary vein assemblages. Parental melts calculated from the fresh analyses contain 9.6–12.6 wt% Al2O3 and 0.07–0.39 wt% TiO2. The estimates are compatible with a supra-subduction-zone setting involving boninite-like melts. Altered chromite is characterized by lower Al2O3 and MgO, higher total Fe, and lower Mg#, with Cr# values reaching 0.99. Its high Cr# is therefore principally consistent with preferential Al depletion during replacement and does not require a more depleted parental melt. Mn and Zn are generally more variable or enriched in altered domains, whereas TiO2 overlaps between fresh and altered chromite. Calculated ferric ratios are non-monotonic. In one sample, highly altered analyses have lower Ni and higher V than fresh analyses, although low analytical totals limit quantitative interpretation. In another sample, Cr-bearing Mg-chlorite and Ca–Cr–Fe garnet of andradite–uvarovite affinity record local element redistribution without establishing net fluxes or a unique fluid source. The proposed screening workflow separates preserved, replaced, and indeterminate domains before parental-melt reconstruction.