Mantle and Recycled Oceanic Crustal Components in Mantle Xenoliths From Northeastern China and their Mantle Sources

The subduction of the Paleo-Pacific plate is widely credited for the destruction of the eastern North China Craton. However, how the Pacific plate subduction has affected the off-craton lithospheric mantle in northeastern China is less clear, as few studies have focused on the lithospheric mantle-derived xenoliths in that region. We report petrography, mineral and rock chemistry, and in situ isotopic compositions of Sr in clinopyroxene and O in olivine for 20 peridotite and 11 pyroxenite xenoliths hosted by the Cenozoic volcanic rocks at Jiaohe and Shuangliao localities. The peridotites include lherzolites, harzburgites, and a wehrlite, many are metasomatized. Group 1 garnet pyroxenites have high Al2O3, Ni, and Mg#; positive Eu and Sr anomalies; and olivine delta O-18 values of 4.8-5.1, which we attribute to recycling of oceanic crustal components to the asthenosphere and their reactions with host peridotites. Groups 2 and 3 pyroxenites are garnet-free and contain peridotite-like pyroxenes; we argue that they were formed by reactions of lithospheric peridotites with evolved melts derived from recycled oceanic crust. In addition, one pyroxenite contains orthopyroxene surrounded by fine-grained olivine and clinopyroxene, while another pyroxenite and the wehrlite contain zoned clinopyroxene with gradual increases in Na2O, (La/Yb)(N), Sr, and Sr-87/Sr-86 ratios and decreases in Ti/Eu from core to rim. These characteristics record infiltration of a carbonatite melt shortly before the transport of the xenoliths. The inferred carbonatite melt has Sr-87/Sr-86 >= 0.70415 and mantle-like olivine delta O-18 and originated from carbonated asthenosphere. Our results, together with previous studies on the host basalts, suggest that subducted crustal materials were initially transported to the asthenosphere beneath northeastern China to produce carbonate-bearing domains. Upwelling of the carbonated asthenosphere produced carbonatite melts that migrated upward and metasomatized the overlying lithospheric mantle.