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

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 delta O-18 values of olivine (ol), orthopyroxene (opx) and clinopyroxene (cpx) vary from 5.10 to 5.98 parts per thousand, 5.46 to 6.78 parts per thousand, and 5.06 to 631 parts per thousand, respectively. Olivine and opx have delta O-18 values similar to-, or above the "expected" mantle range, whereas the delta O-18 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 delta O-18 values of ol and opx and low delta O-18 values of cpx are unlikely to result from selective interactions with the fluids with different delta O-18 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-delta O-18 fluid/peridotite interaction followed by a late low-delta O-18 fluid infiltration. Model calculations of mineral diffusivities predict that the negative Delta O-18(cpx-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 similar to 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. (C) 2015 Elsevier B.V. All rights reserved.