玄武岩和金伯利岩中斜方辉石的矿物化学特征及其意义

THE MINERAL CHEMISTRY CHARACTERISTICS AND SIGNIFICANCE OF ORTHOPYROXENE IN BASALT AND KIMBERLITE

作者收集了国内外玄武岩和金伯利岩中不同产状的斜方辉石300余个样品的矿物化学资料。通过对这些资料的分析,确定了斜方辉石的成分范围区。研究表明,斜方辉石的Al_2O_3含量随压力增高而增加,但是,当压力超过21.4×10~8-24.9×10~8Pa时,Al_2O_3含量随压力的继续增高而呈减少趋势。产于金伯利岩中的斜方辉石以富Mg,100Mg/(Mg+Fe^(3+)+Fr^(2+)+Mn)值高和极贫Al、Ca为特征;产于玄武岩中的斜方辉石以贫Mg,富Ca、Fe为特点;Ⅱ型包体可能是在高压条件下从寄主岩——玄武岩中结晶出来的,与巨晶具有相似的成因。

The data on mineral chemistry of more than 300 samples different in occurence in basalt and kimberlite are analysed,and the range of composition is determined.The study indicates that the content of Al_2O_3 in orthopyroxene increases with increasing pressure,but when the pressure is higher than 21.4-24.9(10~8pa),the content decreases with increasing pressure.The orthopyroxene occurred in kimberlite has the character- istics of Mg-rich,high value of 100Mg/(Mg+Fe^(2+)+Fe^(3+)+Mn)and Al,Ca-poor;the orthopyroxene in basalt is Ca,Fe-rich and Mg-poor.II inclusions may be crystallization products of their host rock——basalt under higher pressure,similar to the megacryst in origin.