The Darbute ophiolites, located in the southwestern CAOB, are the products of the expansion, subduction, closure of the ancient Asian ocean basin in the CAOB and record the history of formation and tectonic evolution of the ocean basin. Scholars have not obtained a unified understanding of the tectonic background of the formation of Darbute ophiolites. To explore the tectonic evolution process represented by the ophiolite, this author presents a new constraint on the genesis and tectonic setting of the Darbute mantle peridotite through detailed mineral geochemistry and its oxygen isotope study using the mantle peridotite in the Darbute ophiolite as the object of study.Methods: The author conducted a detailed mineral geochemical and oxygen isotopic study of mantle peridotite in the Darbute ophiolite.Results: The olivine Ni/Co values in the Darbute mantle peridotite are 21~22, and the Ni/Mn ratios are 3. 0~7. 8, which represent the residual components of partial melting. In addition, the incompatible elements in the peridotite are deficient relative to the normal mantle peridotite, indicating that the harzburgite is a partial melt remnant component. The spinel Cr# of 47~52, TiO2 content of 0. 01%~0. 04%, and olivine Fo of 90. 34%~90. 98% indicate that the harzburgite experienced >20% partial melting. The values of olivine δ18O olivine +5. 1‰~+6. 2‰ and clinopyroxene δ18Ocpx +5. 6‰~+6. 9‰ in the harzburgite, which vary widely and are generally higher than the δ18O values of olivine and clinopyroxene in the normal mantle. The oxygen isotope fractionation coefficients between minerals Δ18OOpx—olivine average -0. 3‰ and Δ18OOpx—cpx average -0. 7‰, which are significantly different from the equilibrium oxygen isotope fractionation coefficients in the normal mantle, and have obvious metasomatism characteristics. Combined with the characteristics of trace elements depleted in peridotite olivine, it is believed that peridotite may be affected by fluid metasomatism. Comparing the compositions of spinel and clinopyroxene in mantle peridotite produced in different tectonic environments, the major elements of spinel and clinopyroxene in this paper have transitional characteristics between fore- arc and abyssal mantle peridotite, similar to the mantle peridotite formed in the initial stage of subduction.Conclusions: Combining the mineral geochemistry and oxygen isotope characteristics, writers believe that the Darbute mantle peridotite was formed in the initial subduction environment from of the fore- arc region. Initial subduction of the plate leads to the spreading of the pre- arc region to form a new oceanic crust, and the upwelling of asthenosphere material due to decompression melting to form MORB- like melts. With the subduction of the plate, the melting of the crustal source material to form melt/fluid intrusion into the mantle wedge, which greatly enhancing the partial melting of the depleted mantle and forming the refractory harzburgite. At the same time, high δ18 O fluids formed by dehydration of Crustal sourced material during subduction interacted with mantle peridotites resulting in an unbalanced oxygen isotopic signature between minerals and minerals. The Darbute peridotites were formed by the interaction between peridotites and the MORB- like melt of upwelling asthenosphere, the melt/fluid from subducted crustal material.