Late Neoarchean magmatic evolution and tectonic significance in the southern margin of the Yinshan Block, North China Craton

The North China Craton, as one of the oldest cratons globally, preserves a complete record of Neoarchean (2.7–2.5 Ga) crustal evolution in its western Yinshan Block. However, there remains controversy regarding the late Neoarchean crustal evolution process and geodynamic setting of the Yinshan Block. Therefore, this study focuses on the rock assemblages in the Wuchuan Xiwulanbulang, Zhulagou, Hongshanzi, and Guyang areas of the Yinshan Block, including TTG gneisses, dioritic gneisses, and monzogranitic gneisses, as well as metamorphic mafic rocks (komatiites, komatiitic basalts, and tholeiites) in the Hongshanzi area. Systematic petrological, geochronological, whole-rock geochemical, and Sr-Nd-Pb-Hf isotopic studies were conducted on these rocks. Combined with previous research findings, we propose that the Neoarchean crustal evolution of the Yinshan Block can be divided into three stages: (1) (~2.7 Ga) dominated by mantle-derived magma underplating and initial continental crust formation, resulting in thickened mafic lower crust and minor TTG rocks; (2) (~2.7–2.53 Ga) characterized by the large-scale formation of TTG rocks and dioritic rock assemblages. The TTG rocks exhibit high (La/Yb)N and Sr/Y ratios, low MgO, Ni, Cr, and Mg# contents, and positive zircon εHf(t) and εNd(t) values. Their geochemical and isotopic features indicate derivation from partial melting of thickened mafic lower crust. The dioritic rocks display geochemical characteristics similar to Archean sanukitoids, likely originating from partial melting of thickened mafic lower crust with minor mantle input. (3) (~2.53–2.50 Ga) marked by the mixing and partial melting of earlier-formed TTG rocks and ancient crust, leading to the formation of potassium-rich granites, signifying the completion of cratonization.

Current understanding of the Neoarchean geodynamic regime in the Yinshan Block remains debated: (1) Some scholars have discovered Neoarchean high-Mg andesites (Archean sanukitoids) and high-Mg basalt-rhyolite bimodal suites in the region, suggesting that Neoarchean crustal growth in the Yinshan Block was primarily driven by plate subduction; (2) Other researchers argue that Neoarchean crustal growth in the Yinshan Block occurred mainly under a mantle plume regime. This study first reports a suite of late Neoarchean (~2.53 Ga) metamorphic mafic rocks in the Hongshanzi area. Through comprehensive petrological analysis, whole-rock geochemistry, and Nd-Hf isotopic analysis, these metamorphic mafic rocks are likely to have formed in a tectonic environment involving mantle plume-ridge interaction. Therefore, integrating the geochemical characteristics of coeval TTG gneisses, dioritic gneisses, and potassium-rich granitic gneisses, we propose that Neoarchean crustal growth in the Yinshan Block was primarily driven by mantle plume activity.