Oxygen isotopic compositions of zircons from pyroxenite of Daoshichong, Dabieshan: Implications for crust-mantle in-teraction

Abstract

Oxygen isotopic compositions of zircons from pyroxenite (∼145 Ma) of Daoshichong, Dabieshan have been measured by an ion microprobe. Both within the single grain and among different grains, oxygen isotopic ratios are homogeneous, δ18O = (7.66‰±0.46) & (1 SD, 1 σ = 0.10, n = 22). High δ18O values indicate that the mantle-derived parent magma of Daoshichong pyroxenite have undergone interaction with crustal materials. Combing with other geochemical constraints, the way of crust-mantle interaction is suggested to be source mixing other than crustal contamination. The time interval between crust-mantle interaction and formation of the parent magma of Daoshichong pyroxenite is less than several million years. The crustal component involving in crust-mantle interaction is mafic lower crust, and the parent magma of pyroxenite possibly contain large proportion (>37%) of such lower crust.