The statistic results of the density distribution of Mesozoic intrusive rocks reveal that the density of basic igneous rocks is higher than that of acidic igneous rocks. The spatial density distribution of extrusive rocks and that of intrusive rocks show regularity, i.e., relatively high density or low density areas are concentrated in specific sites. Therefore, to explain the regional tectonics of northern Hebei Province, this paper suggests the existence of a branch of mantle plume, in which high density basic igneous rocks are located at the center and low density acidic igneous rocks are situated on the edge. The structure of the branch plume might have controlled the regional ore-forming process.