Geochemistry of Olivine Melt Inclusion Reveals Interactions Between Deeply Derived Carbonated Melts From the Big Mantle Wedge and Pyroxenite in the Lithospheric Mantle Beneath Eastern Asia

Our current knowledge regarding the distribution patterns of ancient and recent recycled materials, as well as the origin of intraplate basalts in the eastern Asia Big Mantle Wedge (BMW), is limited. To address this, we conducted a detailed geochemical analysis of olivine melt inclusions (OLMI) in nephelinite samples. The normal OLMIs detected in our investigation exhibit geochemical features that closely resemble those of the hosting nephelinite, indicating a consistent association with a carbonated mantle source. Additionally, we identified a distinct group of anomalous OLMIs that displayed different geochemical characteristics from the hosting nephelinite but showed similarities to regional alkali basalts sourced from pyroxenite. The observed geochemical diversity in the nephelinite OLMIs suggests an interaction between deeply derived carbonated melts originating from the flattened Pacific slab in the mantle transition zone and pyroxenite in the lithospheric mantle. Carbonated fluid‐fluxed melting is key to basalt formation in the BMW. Plain Language Summary The Big Mantle Wedge (BMW) refers to the mantle regions situated between the flattened subducted slab in the mantle transition zone (MTZ) and the overlying plates. In order to better understand the distribution patterns of recycled materials and the origin of intraplate basalts within the Eastern Asia BMW, we have focused on studying the Cenozoic basalts from the eastern North China region. Initially, it was believed that these basalts were formed through decompression melting of the mantle caused by back‐arc extension associated with the subduction of the Pacific plate. However, recent studies have revealed unique characteristics of these basalts, such as high water content and isotopic values that differ from those of the depleted mantle. This suggests a possible connection between the basalts and decarbonation and dehydration processes occurring within the stagnant subducted slab in the MTZ. According to the proposed model, carbonated melts/fluids released from the stagnant slab interacted with the lithospheric mantle, resulting in the transformation of the melts and the involvement of pyroxenite in the lithospheric mantle. The pyroxenite forms through ancient melt metasomatism events. This interaction ultimately leads to the generation of basalts with a wide range of SiO2 content. Key Points The olivine melt inclusions (OLMI) originate from either a carbonated mantle source or ancient pyroxenite