Mantle metasomatism facilitates the formation of continental crust and metal enrichment

Earth’s enriched lithospheric mantle is postulated to be a natural repository of gold and rare earth element (REE) concentrations. We reviewed evidence for gold and REE enriched mantle from the Jiaobei and Luxi terranes in the North China Craton (NCC), which are the world’s third largest gold province and the China’s third largest REE deposit, respectively. In both terranes, extensive Archean tonalite–trondhjemite–granodiorite (TTG) suites are exposed, but whether their mantle source and partial melting pressure are different that caused diverse metallogeny remains ambiguous. Based on a comprehensive analysis of geochemical data, zircon U–Pb, and Hf isotopic compositions from the TTGs, we evaluate the petrogenesis, crustal–mantle evolution, and the role of source magma composition in the formation of crust as well as gold and REE mineralization. Zircon U–Pb–Hf isotope systematics reveal that magma emplacement occurred during three major pulses at ca. 2.9 Ga, 2.7 Ga, and 2.5 Ga in the Jiaobei Terrane, whereas magmatism in the Luxi Terrane was largely concentrated from ca. 2.7 to 2.5 Ga. Geochemical and isotopic data show that the ca. 2.9 Ga and ca. 2.7 Ga TTGs in the Jiaobei Terrane are inferred to have been generated by high- and low-pressure partial melting of an enriched mantle wedge and mafic crust of a thickened arc. The ca. 2.6 Ga and ca. 2.5 Ga TTGs in the Jiaobei Terrane were generated from low- to medium-pressure partial melting the crust of a continental arc. The mantle was gradually metasomatized by slab–derived fluids in the Jiaobei Terrane during ca. 2.7–2.5 Ga, and by additional melts from sedimentary protoliths in the Luxi Terrane during ca. 2.6–2.5 Ga. The spatial distribution of isotopic and geochemical patterns of TTGs reveals the presence of a heterogeneous enriched lithospheric mantle beneath the Jiaobei and Luxi terranes, formed by variable degrees of metasomatism and experienced variable degrees of partial melting. We propose that mantle metasomatism induced by melts derived from sedimentary precursors and low-pressure partial melting played an important role in the formation of the REE deposits and gold fertility within the SCLM.