A metasomatized mantle wedge origin for low-delta O-18 olivine in late Cretaceous Junan and Qingdao basalts in the Sulu orogen

作者：Guo Feng^*; Guo JiangTao; Wang Yan; Fan WeiMing; Li ChaoWen; Li HongXia; Zhao Liang

来源：Chinese Science Bulletin, 2013, 58(32): 3903-3913.

DOI：10.1007/s11434-012-5607-z

• metasomatized mantle wedge
• subducted oceanic crust
• low-delta O-18
• olivine
• late Cretaceous
• North China Block

The North China Block (NCB) experienced extensive lithospheric thinning and subsequent mantle accretion in the Mesozoic to Cenozoic, but their mechanism remains controversial. This paper reports in situ chemical and oxygen isotope analyses on olivine xenocrysts and porphyroclastic olivines in mantle xenoliths hosted in the late Cretaceous basalts from Junan and Qingdao, the Sulu orogen. The results show that all these olivines have low delta O-18 values relative to normal mantle peridotite. The olivine xenocrysts and porphyroclastic olivines from Junan have Fo=87.5-89.8, delta O-18=4.1aEuro degrees aEuro"5.2aEuro degrees with an average of 4.8aEuro degrees; the porphyroclastic olivines from Qingdao also have Fo=89.0-89.9, delta O-18=4.1aEuro degrees aEuro"5.2aEuro degrees with an average of 4.8aEuro degrees. These peridotite xenoliths have petrological and geochemical affinities similar to newly accreted MORB-type mantle, we hence consider such low-delta O-18 features in the olivines to inherit from a mantle wedge that was metasomatized by melts derived from the subducted oceanic crust, which had experienced high-temperature hydrothermal alteration to acquire the low-delta O-18 signatures. Combined the existence of Cenozoic low-delta O-18 basalts and garnet pyroxenite xenoliths (relicts of recycled oceanic crust) hosted in Cenozoic basalts in the NCB, the subducted oceanic crust likely played an important role in the lithospheric evolution of the NCB during the Mesozoic to Cenozoic.

• 出版日期2013-11
• 单位中国科学院; 中国科学院广州地球化学研究所; 同位素地球化学国家重点实验室