Paleoproterozoic A1- and A2-type coexisting monzogranites in the Daqingshan Complex, Khondalite Belt, North China Craton and its tectonic implications

Abstract

Paleoproterozoic granitoids, widely exposed in the Daqingshan Complex in the Khondalite Belt of North China Craton (NCC), are of great significance for understanding the magmatic evolution and tectonic setting of the blet. Zircon LA-ICP-MS U-Pb dating results of four monzogranite samples are 2385 ± 18 Ma, 2358 ± 24 Ma, 2437 ± 32 Ma, and 2338 ± 24 Ma. Zircon Lu-Hf isotopic analysis shows that the monzogranites have positive εHf(t) values of +0.5 to +4.5, with two-stage Hf model ages (TDMC) range from 2859 to 2617 Ma, indicating that these rocks were mainly produced from ancient crust through the process of assimilation-fractional crystallization. The Daqingshan monzogranites are high-K calc-alkaline to shoshonite series, metaluminous to peraluminous series, enriched in large-ion lithophile elements (LILEs, such as Rb, Ba, La, and Ce) and depleted in high field strength elements (HFSEs) such as Nb, Ta, and Ti. They have low Sr/Y (3.48–35.72) and (La/Yb)N (4.79–46.50) ratio and weakly Eu negative anomalies (δEu = 0.14–1.23), indicating that they were formed in the continental magmatic arc environment. In addition, the monzogranites have high alkaline (Na2O + K2O) and SiO2 components, and high Ga/Al and HFSE values, showing the coexistence of A1- and A2-type granitoids. Combined with previous studies, our new results provide that the Khondalite Belt underwent magmatic events from 2.44 to 2.34 Ga during a long-lived arc-continental accretion process along the southern margin of the Yinshan Block. However, the Daqingshan monzogranites do not preserve records of Paleoproterozoic collisional event at 1.95–1.85 Ga in the Khondalite Belt, indicating that they did not experience subduction-related metamorphism and subsequent collision. Thus, the Daqingshan monzogranites may represent the post-collisional to late orogenic granitoids during the transition from compressive to rift tectonics following collision between the Yinshan and Ordos blocks.