Petrogenesis and tectonic setting of Neoarchean K-rich granitoids in the Zhulagou area: Implications for the crustal maturation of Yinshan Block, western North China Craton

• Emplacement of the Zhulagou K-rich granitoids occurred at 2.52–2.50 Ga. • Zhulagou K-rich granitoids from the partial melting of a thickened lower crust. • Partial melting of the lower crust triggered by Neoarchean mantle plume activity. K-rich granitoids are considered as an indicator of the maturation of the continental crust, particularly in correlation to the significant crustal evolution during the Neoarchean Eon. The Yinshan Block, a typical Neoarchean microcontinental block of the western North China Craton (NCC), preserves several typical K-rich granites (monzogranitic gneisses). However, their petrogenesis and tectonic background of these remain unclear, hindering our understanding of the late Neoarchean crustal evolution of the NCC. This study presents new geochronological, geochemical, and Sr-Nd-Pb-Hf isotopic data on the K-rich granites exposed in the Zhulagou area, a key exposure of the Yinshan Block. Zircon U–Pb dating results suggest that the K-rich granites were emplaced at 2.52–2.50 Ga. The K-rich granites exhibit high SiO 2 (68.70–74.10 wt. %) and K 2 O (3.40–7.79 wt. %) and lower MgO (0.24–1.04 wt. %) content. They also have high Sr/Y and (La/Yb) N ratios, as well as low Y and Yb contents. Furthermore, they display variable ε Hf ( t ) (–1.1 to +2.5) and ε Nd ( t ) (–6.05 to +1.64) values, with relatively low Pb isotopes ( 206 Pb/ 204 Pb (t) = (13.910485–15.241164), 207 Pb/ 204 Pb (t) = (14.806723–15.259938), and 208 Pb/ 204 Pb (t) = (33.758621–35.592727)), indicating that their parental magmas may have originated from the partial melting of a thickened lower crust with heterogeneous sources. Combined with previous data, we suggest that a pulse or stage of mantle plume may have been operating under the Yinshan Block during late Neoarchean period. The pre-existing thickened (mafic) lower crust was partially melted to generate these K-rich granites at 2.52–2.50 Ga, resulting in a mature and stable continental crust.