伊通新生代玄武岩中辉石岩捕虏体的尖晶石成分分带

Compositional Zoning in Spinel in Pyroxenite Xenoliths from the Yitong Cenozoic Basalt,Northeast China

伊通新生代玄武岩中存在3种不同成因的捕虏体，其中上地幔岩浆分异结晶形成的辉石岩捕虏体中尖晶石具有独特的成分分带。电子探针分析显示在尖晶石矿物的边缘富Al，而贫Mg、Fe和Cr，矿物中心富Mg、Fe和Cr，而贫Al，从中心向两侧基本对称。从尖晶石成分分带的元素分布特征判断，其形成不是固溶体相平衡过程中的离子扩散，而可能是化学平衡过程中结晶矿物与熔浆之间化学成分平衡的结果，属于化学平衡导致的成分分带。从尖晶石矿物中心到边缘的温度变化不能反映矿物形成后所经历的温度变化状况，与尖晶石共生矿物的二辉石地质温度计所能代表的地质意义是矿物中心的温度（～1006℃）．反映矿物开始结品时的温度状态。

The lherzolite, wehrlite and pyroxenite are the three types of xenoliths tong Cenozoic basalt, Northeast China. The spinel in pyroxenite xenoliths has special ning. It is suggested that the pyroxenite xenoliths were formed by the crystallization the differentiated mantle-derived magma. Based on electron microprobe analysis, the found in the Yicompositional zo- differentiation of spinel is featured by symmetrical compositional zoning with A1 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 diffu- sion 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℃）.