Early Precambrian evolution of the Qixia area, eastern North China Craton:Evidence from geological mapping and SHRIMP U-Pb zircon dating

Qixia is a typical area of Early Precambrian basement in eastern Shandong, North China Craton. Many TTG rocks were once considered to be supracrustal rocks (the Jiaodong Group), and the formation ages of the rocks have only been determined in a few outcrops in the original geological map (1:50000) of the area. In this study, the authors carried out geological mapping and SHRIMP U-Pb zircon dating on more than 30 samples in order to determine the temporal and spatial distribution of the TTG rocks. In the newly compiled geological map (1:50000), the main rock types of the Archean basement are tonalite gneisses with ages~2.9Ga, ~2.7Ga and~2.5Ga and some local trondhjemite gneisses of the same ages. Supracrustal rocks of~2.9Ga and~2.5Ga (the Huangyadi supracrustal rocks and the Jiaodong Group) are very rare. All of the rocks roughly extend in a NWW-SEE direction, probably as a result of the strong late Neoarchean and late Paleoproterozoic tectonothermal events.