The origin of Neoarchean granitoid diversity in the Yinshan Block and its implications for the crustal evolution of the North China Craton

Abstract

Neoarchean TTG and K-rich granitoids in the Yinshan Block provide a key to understanding the crustal evolution of the North China Craton (NCC), such as the change of continental crust composition, the micro-continent collision and the cratonization. Zircon U-Pb dating suggests that these Neoarchean TTG and K-rich granite rocks were emplaced at 2.7–2.5 Ga and ∼2.5 Ga, respectively. The TTG rocks have low Cr, Co, and Ni contents and Mg^# values, indicative of a crustal source. The ∼2.7 Ga Kuluedianlisu granodiorites have positive ε_Hf(t) values ranging from +6.6 to +9.3, with crustal model ages (T_DMC) of 2.59–2.75 Ga, indicating that they were formed by partial melting of juvenile lower crust. The Hejiao and Dajitu TTG rocks show lower positive ε_Hf(t) values (+3.4 to +5.6) and older crustal model ages (T_DM^C = 2.53–2.83 Ga) than the Kuluedianlisu granodiorites, demonstrating an origin of partial melts from the pre-existing lower crust. The Rentaihe K-rich granites show higher Sr/Y and (La/Yb)_N ratios which similar to the high pressure sodium TTG rocks. They have low ε_Hf(t) values varying from −1.7 to +4.9, with crustal model ages (T_DMC) from 2.7 to 3.1 Ga. Therefore, it is reasonable to suggest that the Rentaihe K-rich granites were produced by remelting of preexisting TTG rocks. According to the complied Hf isotopic compositions, the crustal model age peaks at 2.6 – 2.7 Ga and 2.7 – 2.8 Ga, indicating a crucial period for crustal growth in the Western Block. In the Neoarchean, the K₂O/Na₂O, the A/CNK ratios, and δ¹⁸O values increased from ∼3.1 Ga to ∼2.5 Ga, indicating a rise of crustal maturity. The crustal thickness simulations show that the crust of the NCC thickened continuously from ∼3.1 Ga to 2.5 Ga. Thus, we conclude that the increasing of crust thickness is induced by the amalgamation of micro-continents through collision and the more buried supracrustal material into deep crust. Subsequent partial melting of the deep crust generated magmas with high δ¹⁸O values and thus resulted in the formation of more mature continental crust.