Recycled oceanic crust-derived fluids in the lithospheric mantle of eastern China: Constraints from oxygen isotope compositions of peridotite xenoliths

• We report δ18O of minerals in peridotite xenoliths from Subei basin.
• Both relative high and low δ18O values are preserved in olivine, opx and cpx.
• The metasomatism fluid(s) is probably from subducting Pacific plate.

The oxygen isotope compositions of minerals of peridotite xenoliths from the Subei basin, Eastern China were investigated to detect a possible crustal signature in mantle rocks. The δ18O values of olivine (ol), orthopyroxene (opx) and clinopyroxene (cpx) vary from 5.10 to 5.98‰, 5.46 to 6.78‰, and 5.06 to 6.31‰, respectively. Olivine and opx have δ18O values similar to-, or above the “expected” mantle range, whereas the δ18O values of cpx range from higher to lower than average mantle. These characteristics are inherited from the peridotite mantle source, and likely result from mantle domains that experienced fluid-assisted metasomatism. Coexisting high δ18O values of ol and opx and low δ18O values of cpx are unlikely to result from selective interactions with the fluids with different δ18O values during a single metasomatic event. The measured O-isotope values can be reconciled with a simple two-stage metasomatic model characterized by an early high-δ18O fluid/peridotite interaction followed by a late low-δ18O fluid infiltration. Model calculations of mineral diffusivities predict that the negative Δ18Ocpx-ol values are unlikely to be preserved at mantle conditions for time interval > 80 Ma. Provided the investigated mantle xenoliths were entrained and brought to surface by ~ 9 Ma basaltic eruptions, this also limits the occurrence of the late metasomatic event, and the subducting Pacific plate is the best candidate to provide such fluids.

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