Oxygen Isotopes of Cr-Spinel as a Pathfinder for Metasomatism in Mantle Peridotites

作者：Qi‐Qi Pan, Yan Xiao, Ben‐Xun Su, Bin Fu, Pengfei Zhang, Paul T. Robinson, İ̇brahim Uysal, Ian S. Williams · 发表于：Journal of Petrology · 年份：2025 · DOI：10.1093/petrology/egaf055 · 被引用次数：4 · 研究领域：Geological and Geochemical Analysis、High-pressure geophysics and materials、Paleontology and Stratigraphy of Fossils

Abstract Debate continues over whether Cr-spinel in mantle peridotites is formed by partial melting or metasomatism. This first systematic report of SIMS oxygen isotope data for the constituent minerals, particularly Cr-spinel, in chromitites, dunites and harzburgites from the mantle sequence of the Lycian ophiolite (SW Türkiye) provides compelling evidence for the latter. The δ18OVSMOW values of Cr-spinel are relatively low across the three rock types, ranging from 2.00‰ to 4.81‰ in chromitites, 1.04‰ to 3.73‰ in dunites, and 1.89‰ to 4.87‰ in harzburgites. The δ18O values of olivine are relatively higher and more uniform, decreasing from chromitites (5.25–6.68‰) to dunites (4.99–5.65‰) and harzburgites (4.90–5.44‰). The δ18O values of orthopyroxene and clinopyroxene in the harzburgites are comparable, ranging from 5.18‰ to 6.63‰ and 5.14‰ to 6.56‰, respectively. Oxygen isotopic compositions of minerals exclude any influence from low-temperature alteration. Cr-spinel in the chromitites shows decreasing δ18O with increasing Cr# and lower δ18O when amphibole is present, suggesting that magma differentiation significantly influences Cr-spinel composition, while the presence of water can significantly lower the Cr-spinel δ18O. The δ18O values of olivine in chromitites increase with increasing Fo contents, indicating re-equilibration between olivine and Cr-spinel. In harzburgites, Cr-spinel shows a negative correlation between δ18O and Cr#, similar to the characteristics of Cr-sp...