Highly siderophile elements and Os isotope constraints on the genesis of peridotites from the Kızıldağ ophiolite, southern Turkey

In this contribution, we present whole-rock major and trace element chemistry, including rare earth elements (REE), highly siderophile elements (HSE), and Re-Os isotope data, together with mineral chemistry for the harzburgites and dunites from the Kızıldağ ophiolite of SE Turkey, in an attempt to better constrain its petrogenesis. Both the harzburgites and dunites have refractory compositions with CaO contents <0.90 wt%, Al₂O₃ contents <0.90 wt% and TiO₂ contents <0.01 wt%, indicating that they experienced high degrees of partial melting in the supra-subduction zone (SSZ) setting. Besides, the concave-shaped REE patterns and positive anomalies in some incompatible elements (e.g., Cs, Rb and Pb) suggest that the harzburgites and dunites have also experienced interactions with percolating melts after partial melting. Based on the quantitative melt-rock interaction model, the addition of sulfides derived from the percolating magmas could be responsible for the variable HSE contents and suprachondritic Pd/Ir and Pt/Ir ratios observed in some of the harzburgite samples. The extremely low HSE contents in the dunites can be explained by interaction with S-undersaturated melts. Enrichments of Os and Ru in two dunites could be attributed to the precipitation of a higher amount of spinel grains along with the possible Os-Ru microparticles. The significantly wide range of Os isotopic ratios in the harzburgites (¹⁸⁷Os/¹⁸⁸Os_{(90 Ma)} = 0.12152–0.13584; γOs_{(90 Ma)} = −4.31 to 6.96) and dunites (¹⁸⁷Os/¹⁸⁸Os_{(90 Ma)} = 0.12690–0.13267; γOs_{(90 Ma)} = −0.08 to 4.47) seems to be consistent with the multi-stage evolution of the oceanic upper mantle. The low Os isotopic ratios (sub-primitive mantle) in some harzburgite samples suggest the lithospheric mantle has experienced ancient melting processes (>1.0 Ga).