Abstract:In this paper, the authors investigated in detail chemical composition of clinopyroxene from the Late Cretaceous shoshonite in Guangfeng and Yushan basins on the basis of electron microprobe analyses. The results show that all clinopyroxenes are composed of augite,which contains relatively low Al2O3 (2.34%~4.13%), high TiO2 (1.19%~2.78%) and Na2O (0.35%~0.49%), showing a typical alkaline series. The crystallization temperature and pressure of clinopyroxenes from the Late Cretaceous shoshonite in Guangfeng and Yushan basins are estimated by the formula that p(0.1 GPa)=-7.538 3+83.169 2(Al), t(℃)=1 056.898 6+902.797 8 (Al) from Thompson et al. (1974). The results show that the crystallization temperatures and pressures of clinopyroxenes are 1 151~1 202℃ and 0.12~0.58 GPa respectively. The clinopyroxenes resulted probably from fractional crystallization of relatively primitive magma in shallow magma chambers, equivalent to the upper crust. These clinopyroxenes were identical with clinopyroxenes in alkaline olivine basalt in the shallow source in such aspects as mineral chemical characteristics and formation environment but slightly different from clinopyroxene phenocrysts in the alkali olivine basalt in the deep source. They are evidently different from the tholeiite in mineral chemical characteristics. In addition, the compositions of the clinopyroxenes are consistent with those in intraplate basalt.