TECTONIC ENVIRONMENT OF THE CENOZOIC BASALTS IN JIXI BASIN, HEILONGJIANG PROVINCE

Study on the petrology, petrochemistry and geochemistry for the Cenozoic basalt in Jixi basin, Heilongjiang Province shows that olivine inclusions are developed in the rock. The olivine crystals are common among the rock-forming minerals. The δEu values of the basalt range from 0.87 to 0.94 (greater than 0.7), showing the characteristics of basic magmatic differentiation. The trace element Nb^* value (2Nb_N/[K_N+La_N]) is 0.91 (close to 1) and K^* value (2K_N/[Ta_N+La_N]) is 1.09 (slightly larger than 1), indicating that the magma is not closely related to the subduction, but with addition of non-crustal materials. In general, the magma originates from the upper mantle, with contamination of crustal materials in the process of uplifting. The Jixi Cenozoic basalt magma is the product of rifting, derived from upper mantle, belonging to continental rift basalts. Its forming is related to the extension of the Dun-Mi fault in Pliocene.