Orogenic Peridotite Origins and Crust-Mantle Interactions in Continental Subduction Zones

Metasomatism of the mantle wedge by crust-derived fluids is a crucial mechanism responsible for subduction zone magmatism. However, how crust-mantle interactions proceed in continental subduction zones is poorly understood. Orogenic peridotite is a direct, ideal sample to resolve this issue. Through combined studies of mineralogy, petrology and geochemistry for on Dabie-Sulu orogenic peridotites, it is found that the Ni/Co ratio of olivine can successfully discriminate between mantle and crustal peridotites, and that mantle-derived peridotites originated from the subcontinental lithospheric mantle wedge beneath the North China craton. The Lijiatun dunites (Sulu) derived from such lithospheric mantle wedge were likely modified by carbonatitic melts prior to their incorporation into the subduction channel. The Maowu (Dabie) and Jiangzhuang (Sulu) peridotites and their metasomatic veins record slab-mantle interaction processes at depths of ~170-200 km. Deeply subducted continental crust would release Si-Al-rich melts to heterogeneously modify the lower margin of the mantle wedge, which could result in forming various garnet- and pyroxene-rich metasomatites and in generating significant Os isotope fractionation. Such processes can not only modify lithological and geochemical compositions of the mantle wedge but also affect crust-derived melt compositions. Recycled heterogeneous peridotites and metasomatites could contribute to the mantle sources of various subduction-related mantle magmas. Therefore, deep continental subduction is a crucial mechanism responsible for the mantle heterogeneity. © 2019, Editorial Department of Earth Science. All right reserved.