Chromite as a key player on highly siderophile elements and osmium isotope compositions of the refractory mantle
Ben-Xun Su, Ibrahim Uysal, Qi-Qi Pan, Paul T. Robinson, Recep Melih Akmaz, Yilmaz Demir, Lukas Ackerman
article (Uluslararası, Hakemli) | Yazar(lar): Ben-Xun Su, Ibrahim Uysal, Qi-Qi Pan, Paul T. Robinson, Recep Melih Akmaz, Yilmaz Demir, Lukas Ackerman | Yıl: 2026 | Dergi/Kurum: GEOCHIMICA ET COSMOCHIMICA ACTA | İndeks: WOS.SCI | DOI: 10.1016/j.gca.2025.04.026 | Anahtar Kelimeler: Chromite, Peridotite, Ophiolite, Re-Os
Chromitites in ophiolites are recognized for their high concentrations of highly siderophile elements (HSE), notably IPGE (Os, Ir and Ru). However, the effects of this enrichment on ophiolitic rocks and mantle heterogeneity remain poorly understood and to address this issue, we investigated chromitites from the Pozant & imath;-Karsant & imath; and K & imath;z & imath;lda & gbreve; ophiolites in T & uuml;rkiye. The results reveal HSE enrichment, particularly IPGE, in chromite separates compared to matrix, with indistinguishable Os isotope compositions between the two phases. This observation aligns with the presence of platinum-group minerals (PGM) occurring as inclusions within chromite grains. The IPGE enrichment and similar Os isotope compositions are also present in chromitites relative to dunites, suggesting close affinity of HSE with chromite fractions relative to silicate melts during chromite crystallization and aggregation. A global compilation of data on chromitites in ophiolites demonstrates covariations of HSE and their ratios with chromite Cr# values, indicating that chromite composition modulates its capacity to retain HSE. Peridotites containing chromite with low-Cr# (<45) exhibit consistent HSE concentrations and a decrease in Os-187/Os-188(t) ratios as chromite Cr# values increase, reflecting different partial melting degrees. In contrast, the refractory peridotites (with chromite Cr# > 45) show more scattered HSE variations and distinct trends with chromite Cr#, generally trending towards the chromitite field. This variability likely reflects the compositional effects of chromite on HSE variations, suggesting significant metasomatism and interaction with parental melts of chromitites or evolved melts. Therefore, chromite plays a critical role in the variations of HSE contents and Os-187/Os-188 within the refractory mantle.