Geochemical constraints on the nature of Late Archean basaltic-andesitic magmatism in the North China Craton

• Published in: Earth-science reviews 2022-07, Vol.230, p.104065, Article 104065
• Main Authors: Wang, Xi, Zhu, Wen-Bin, Zheng, Yong-Fei
• Format: Article
• Language: English
• Subjects: Basalt geochemistry; Greenstone belt; Late Archean; Mafic magmatism; Oceanic subduction
• ISSN: 0012-8252; 1872-6828
• DOI: 10.1016/j.earscirev.2022.104065

The North China Craton (NCC) is distinguished from the majority of Archean cratons in the world by its extensive records of late Neoarchean (2.6–2.5 Ga) mafic magmatism but its rare records of early Neoarchean (ca. 2.8–2.7 Ga) magmatism. Controversial issues have long existed on the tectonic setting of these mafic magmatisms, and it has been enigmatic about the role that the NCC has played in the Archean global tectonics. These issues are addressed by an integrated study of whole-rock major and trace elements as well as zircon Hf and whole-rock Nd isotopes in late Archean basaltic-andesitic rocks from the NCC. There are three episodes of basaltic-andesitic magmatism at ca. 2.88–2.73 Ga, ca. 2.65–2.60 Ga, and ca. 2.56–2.50 Ga, respectively. The first two phases are almost entirely tholeiitic basalts, whereas the last phase is composed of tholeiitic basaltic rocks, tholeiitic andesitic rocks and calc-alkaline rocks. The tholeiitic suites can be subdivided into LREE-depleted and LREE-enriched types in terms of their (La/Sm)N ratios, and the calc-alkaline suites are categorized into conventional andesitic rocks and sanukitoids according to their La/Yb and Sr/Y ratios as well as Sr and Ba concentrations. These rocks show island arc basalts (IAB)-like trace element distribution patterns and high water contents, indicating their formation through subduction zone magmatism. The LREE-depleted basaltic rocks were derived from partial melting of a mantle source that was weakly metasomatized by subduction zone fluids (mainly aqueous solutions), whereas the LREE-enriched basaltic rocks were originated from a mantle source that was significantly metasomatized by subduction zone fluids (including both aqueous solutions and hydrous melts). The tholeiitic andesitic rocks were generated by magma differentiation of the tholeiitic basaltic rocks. The coexistence of LREE-depleted and LREE-enriched tholeiitic rocks resembles the bimodal rock assemblage in backarc basins above modern oceanic subduction zones. The calc-alkaline andesitic rocks and sanukitoids were produced by partial melting of metasomatic domains that were generated by reaction of the mantle wedge peridotite with the hydrous melts, but the mantle source of sanukitoids contain more crustal components with higher melt/peridotite ratios of >0.1, in which the metasomatic agent would contain variable amounts of the low-degree partial melt from dehydrated melting of the subducting basaltic crust. The dominance of thol