西准噶尔玉依塔勒盆克提斑岩体中石榴子石的发现及地质意义

The Discovery of Garnet from Yuyitalepenketi Granite Porphyry in Western Junggar and its Geological Significances

为探讨位于新疆玉依塔勒盆克提一带的石榴子石花岗斑岩中石榴子石的成因类型,结合野外地质、岩相学、矿物学研究,分析了石榴子石的端元组分。结果表明,该区石榴子石为自形晶体,呈斑晶分布于整个花岗斑岩中,而非岩体边部,为岩浆结晶石榴子石,其中含有大量早期晶出的磷灰石。电子探针分析表明,石榴子石具有高铁、相对富钙而贫锰、镁特征。计算的主要端元组分为：铁铝榴石（62.36%~74.76%mol）,钙铝榴石（10.90%~15.56%mol）,镁铝榴石（6.78%~16.43%mol）,锰铝榴石（4.08%~6.91%mol）。综合区域岩浆活动和构造发展演化阶段的研究成果认为,该花岗岩的形成可能与俯冲作用有关。

In order to probe the genesis of garnet from the garnet-bearing granite porphyry in the Yuyitalepenketi area,Xinjiang,a study on mineralogy and chemical compositions of the garnet has been carried out in this paper based on its field geological and petrographic features. Results show that the garnet occurs as phenocrysts of euhedral crystal distributed in the whole body rather than in the rim of the granite porphyry body. It is believed that those garnets are magmatic ones which contain large amounts of needle or columnar-like apatite inclusions. EPMA analytical results indicate that all garnets are rich in Fe,relatively rich in Ca,but poor in Mn and Mg,with calculated compositions of almandine（ 62. 36 ~ 74. 76 % mol）,grossular（ 10. 90 ~ 15. 56 % mol）,pyrope（ 6. 78 ~ 16. 43 % mol）,and spessartine（ 4. 08 ~ 6. 91 % mol）. These results suggested that the garnets crystallized early and are magmatic in origin rather than being xenocrysts or restite phases. Combining with previous researches on magmatic activities and structural development evolutions of the region,it is believed that formation of the granite in the region could be associated with the subduction-related magmatism.