内蒙古太古宙变质岩系中石榴石的矿物学特征及其地质意义

Some Mineralogical Characteristics of Garnet in Archeozoic Metamorphic rocks of Inner,Mongolia and Its Geological Significance

本文对内蒙古南部太古宙集宁群变质岩系中6个石榴石样品进行了研究,讨论了晶体形态、物理性质、化学成分与岩石成分和波谱学之间的关系。研究表明,本区(含石墨)富铝片麻岩类岩石中,石榴石以富镁的铁铝榴石组份为主,而二辉石岩中的石榴石则以富钙的铁铝榴石组份为主。石榴石钙的含量受岩石成分所控制。从测得的晶胞参数来看,除个别者外,a_0值均随着Ca^(2+)的含量增加而增大。据穆斯堡尔谱分析,本区集宁群变质岩系中除个别样品受到了氧化或蚀变而有Fe^(3+)成分混入外,大部分石榴石可能都是在变质程度比较高的还原环境下形成的。

Based on a study of six garnet samples from Archeozoic metamorphic rocks in Inner Mongolia, this paper discusses the relationship of crystal shape, physical properties, chemical composition of garnets and components of the rocks to spectroscopy as well as the formation condition of garnets.The end member components calculated from mineral composition indicate that the garnets in aluminous gneiss consist mainly of Mg-rich almandine, while those in amphibole websterite are composed chiefly of Ca-rich almandine. Chemically, calcium content of garnets is as a rule rather low, controlled by composition of the host rocks. With very few exceptions, the ceil parameter (a_0) grows larger with the increasing Ca^(2+) content.It is considered from an analysis of Mssbaurer spectra that garnets in metamorphic rocks of Jining Group might have mostly been formed under areduction conditions.