Prolonged Slab-derived Silicate and Carbonate Metasomatism of a Cratonic Mantle Wedge (Maowu Ultramafic body, China)

作者：Yi Zhao, Jianping Zheng, Qing Xiong · 发表于：Journal of Petrology · 年份：2021 · DOI：10.1093/petrology/egab081 · 被引用次数：16 · 研究领域：Geological and Geochemical Analysis、High-pressure geophysics and materials、earthquake and tectonic studies

Abstract Mass transfer between crust and mantle at continental margins is a crucial process in shaping mantle heterogeneity and material cycling in deep Earth. Mass transfer is usually archived by the slab-derived and/or asthenosphere-derived component, which metasomatize a cratonic mantle wedge. Clarifying the origin and temporal sequences of these records is a fundamental aim yet is poorly resolved. Comprehensive petrography, whole-rock and mineral compositions [including platinum group elements (PGE)], zircon U–Pb ages, trace elements, and Hf isotopes of the Maowu ultramafic body (comprising harzburgites and garnet orthopyroxenites) in the Dabie orogen (Central China) are presented in this study to decode the complex metasomatic histories beneath the southern North China Craton (NCC). The ultramafic body represents a typical cratonic mantle-wedge fragment with an equilibration pressure of 4·0 ± 1·0 GPa and temperature of 750 ± 50 °C. The harzburgites have high Mg# values (up to 92) and Ni contents (2537–2892 ppm), low Al2O3 (0·26–0·76 wt%) and CaO (0·05–0·32 wt%) contents, and high olivine Fo values (91–93), supporting the origin from a cratonic mantle wedge with partial melting extents of ~20–25 %. Garnet orthopyroxenites occurring as veins in the harzburgites have a wide range of Mg# values (83–91), high Ni contents (963–2353 ppm), and significant enrichment in light rare earth elements and large ion lithophile elements. They show PGE contents and patterns similar to tho...