Archean crustal formation and evolution of the Lushan area in the southern margin of the North China Craton

Archean basement rocks are well preserved in the Lushan area. In this study, zircon SHRIMP U-Pb dating results suggest that two samples, collected from the Weizhuang gneiss in Lushan, record magmatic age of 2867±5 Ma and 2768±5 Ma, respectively. They underwent metamorphism at 2775±6 Ma and 2775±56 Ma, respectively. Together with data available, the protoliths of the Weizhuang Gneiss formed at two stages, i.e., 2867-2928 Ma and 2765-2768 Ma, while protoliths of the Yushuzhuang Gneiss and amphibolite formed at three stages (2829-2897 Ma, 2752-2778 Ma and 2723 Ma versus 2838-2845 Ma, 2747-2794 Ma and 2730 Ma). Although the three types of rocks are different in lithology, they record similar magmatism phases, indicating the existence of genetic connections among them. Recently, 2.8-2.9 Ga rocks were identified in many areas, indicating the existence of Mesoarchean basement on a certain scale in Lushan. Compared with the Precambrian evolution of Jiaodong and Huoqiu, it is concluded that a Mesoarchean block, which underwent a significant crustal growth event at 2.9-3.0 Ga, may be present along the southern margin of the North China Craton.