玄武岩中包体橄榄石的分带现象

THE ZONAL STRUCTURE OF OLIVINE IN INCLUSIONS WITHIN BASALTS

报道了浙江衢县、福建明溪等地新生代玄武岩中尖晶石(石榴石)二辉馓榄岩包体和捕虏晶中发现的橄榄石成分分带现象。给出了电子探针分析结果,总结并讨论了这种分带的特点、成因以及不同地区之间的差别。

Zonal distribution of Mg, Fe and even minor elements Ca,Mn was observed in olivine crystals during analysis of lherzolite inclusion and renocrysts from Cenozeic basalts in Quxian of Zhejiang and Mingxi of Fujian on electron-probe. It is a simple, gradual transitional and symmetrical distribution in xinocrysts. The core of xenocryst is Mg-rich and becomes iron-rich gradually outward to rim, Fo of olivine varies in a range of 72—90％ which belongs to a range of chrysolite. The zonal distribution of elements is found in the rim of olivine from the inclusion in contact with basalt. In the xenocrysts, almost all larger crystals exhibit zonal structure, except that the small crystals have been homogenized. Apparently, this zonal distribution resulted from the diffusion of elements between basalt magma and olivine. The range and width of olivine zone vary with the type of basalt or its locality. This reflects the difference in temprature, pressure, diffusion time and chemical composition.