Abstract: The lherzolite, wehrlite and pyroxenite are the three types of xenoliths found in the Yitong Cenozoic basalt, Northeast China. The spinel in pyroxenite xenoliths has special compositional zo-ning.It is suggested that the pyroxenite xenoliths were formed by the crystallization differentiation of the differentiated mantle-derived magma. Based on electron microprobe analysis, the spinel is featured by symmetrical compositional zoning with Al increasing and Mg, Fe and Cr decrease from core to rim. According to the characteristics of element distribution, the spinel compositional zonings were formed by the chemical equilibrium between the crystals and magma during magma crystallization, not by ion diffusion in the processes of subsolidus equilibrium. The temperature difference from core to rim does not reflect the real temperature change after crystallization. The temperature in the center part of coexisted clinopyroxene and orthopyroxene can only represent the initial temperature of magma crystallization (~1 006℃).

Key words: compositional zoning, spinel, chemical equilibrium, crystal temperature