| Basalts are the most extensive distributed rocks over the Earth's surface. The geochemistry of oceanic basalts is the foundation of the core theory,"Plate Tectonics"and"Plume Hypothesis"in modern Earth Sciences. Nowadays Re-Os isotopic system has been extensively applied in geochemistry of various basalts, such as mid-ocean ridge basalts (MORB), oceanic island basalts (OIB), continental flood basalts (CFB) and large igneous province basalts (LIP).The Cenozoic basalts from Hannuoba, North China belong to the continental rift basalt. The consensus on the origin and evolution of Hannuoba basalts are almost reached among the researchers based on the previous comprehensive elemental and isotopic geochemical studies. The alkali basalts were derived from the relatively homogeneous asthenospheric mantle, and the tholeiitic basalts were derived from rather heterogeneous enriched mantle. Melts were produced by partial melting of mantle source in different degree, and experienced fractional crystallization in different degrees, of ferro- magnesian minerals under high pressure.The whole rock Re-Os isotopic data of 29 basalt samples from Hannuoba, North China are reported in this thesis. The results show that the Hannuoba basalts have relatively high Os abundances (11-314ppt) and relatively low Re abundances (40-238ppt) within large Re and Os abundance range of OIB, and their Os isotopic ratios (187Os/188Os) range from0.14735 to 0.61136. A positive correlation is observed between Os and Re abundances in Hannuoba basalts, and the Re and Os abundances of alkali basalts are relatively higher than that of tholeiitic and transitional basalts. The positive correlation is observed between the abundances of Re and incompatible trace elements indicating the degree of partial melting in alkali basalts. Also there is the positive correlation between the abundances Os and compatible trace elements indicating the degree of the fractional crystallization in alkali basalts. The both trends reflected the elementary behavior of Re and Os in the partial melting and the fractional crystallization processes. The alkali basalts have slightly radiogenic Os isotopic compositions within narrow range, whereas the tholeiitic and the transitional basalts have more high radiogenic Os isotopic compositions and wide range. A negative correlation is observed between Os isotopic compositions and Os abundances in Hannuoba basalts. The 187Os/188Os ratios raises rapidly as Os abundances decrease below 75 ppt, which reflects that the significant effects of crustal contamination on the origin of the basalts, especially for that of tholeiitic and the transitional basalts. The crustal contamination of Hannuoba basalts showed by Re-Os isotopic systematics is clearer than that by other lithophile isotope schemes, for example, Sr-Nd-Pb isotopes in previous studies. Therefor Re-Os isotopic system is more powerful than Sr-Nd-Pb isotopic systems for tracing crust contamination in petrogenesis. The transitional basalts are indistinguishable with tholeiitic basalts in Re-Os isotope geochemistry, but they are different in other elemental and isotopic aspects in previous studies. A few tholeiitic samples with rather high Os abundance have radiogenic Os isotopic compositions which probable indicates that tholeiitic basalts were derived from"marble cake"mantle, not from normal peridotite mantle.Re and Os abundances, especially Os are extremely low in basalts, it is very important to reduce total procedure blank for Re-Os isotopic scheme analysis. The total procedure blank of Os in our laboratory is ~2pg with optimum condition, but this is still not suitable for basalt study in high quality.
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