For understanding the Mesozoic tectonics of Yanshan (燕山) belt, the authors took geological mapping in the belt. A large-scale thrust structure was identified in Yong’anpu (永安堡) area, in the western part of Suizhong (绥中) County, Liaoning (辽宁) Province during our recent mapping in the Yanshan belt. The hanging wall of the thrust was composed of Archean gneiss and the overlying Early Cretaceous Zhangjiakou (张家口) Formation; meanwhile, the strongly ductile deformed volcanic rocks of Zhangjiakou Formation comprised the footwall in Yong’anpu tectonic window. This discovery indicates the existence of strongly contractional deformation in the Yanshan belt after the eruption of Early Cretaceous Zhangjiakou volcanic rocks. On the basis of mapping and research, it is concluded that the published official geological maps have failed to identify the major structural features of the Yanshan belt.
