The genesis of peridotite in Darbute ohiolite within West Junggar basin, Xinjiang

The peridotites in Darbute ophiolite consist mainly of harzburgite and minor dunite, lherzolite and dunite and exhibit strong alteration. The major elements of clinopyroxene, orthopyroxene, olivine and spinel of harzburgite show the characteristics of both abyssal peridotite and SSZ peridotite, which is identical to the features of the trace elements of clinopyroxene obtained from the LA- ICP- MS in- situ analysis, while lherzolite is similar to abyssal peridotite. Oxygen fugacities recorded by olivine- spinel of harzburgite equilibrium are +0.96 log units below and-0.14 log units above the FMQ buffer, overlapping the range from MOR to SSZ harzburgite, or from back arc basin peridotite to island arc peridotite. The plot of Ga- Ti- Fe3 + #of spinels indicates that theorigin of dunite was related to the interaction between peridotite and island arc tholeiite, and the harzburgite was probably the residue after the interaction between peridotite and MOR melt and the interaction between peridotite and hydrous melt at the SSZ environment. The values of ∑REE of harzburgite and dunite are lower than those of C1 chondrite, and display the enriched LREE and the U-type REE pattern,which implies the fluid/melt-rock reaction. Taking into account the above data, the authors hold that the Darbute ophiolite was probably formed in the back arc spreading ridge and influenced by subducted fluid/melt.