LATE PALEOZOIC, MESOZOIC AND CENOZOIC BASALTS IN EASTERN CHINA AND THEIR GEOLOGICAL SIGNIFICANCE

On the basis of the data of the chemical analyses of whole rocks （844 analyses） and minerals （49 analyses） obtained using the electron microprobe methods, the following conclusions may be drawn. 1. The chemical differences between the late Paleozoic, Mesozoic and Cenozoic basalts in eastern China can be recognized. The late Paleozoic basalts in the Southwestern Yangtze platform and the Paleogene basalts in North China and Northeast China belong to continental tholeiite. The former have higher TiO₂ and F₂O contents and a lower MgO content, as compared with the latter or other basalts. Most of the Mesozoic basalts are high-alumina or calc-alkaline, which have higher SiO₂ and Al₂O₃ contents and a lower TiO₂ content. The Neo- gene and Quaternary basalts are continental alkaline or per-alkaline, which are characterized by higher contents of magnesium and alkali. 2. The late Paleozoic tholeiites and the clinopyroxenes therein have abnor- mal chemical compositions, which contain more than 3. 2% of TiO₂. So it is considered that the depth of the magma generation is greater, and the upper mantle of the Upper Yangtze platform has higher TiO₂ and FeO contents and a lower MgO content than that of North China and Northeast China