- 责任者：Huang Gang (Regional institute ; Shaanxi Bureau of Geological Exploration ; Xianyang 712000 ; China) ; Jia Zhenkui
- 刊名：Xinjiang Geology
- 出版年：2012
- 卷期：30(3)
- 关键词：花岗质片麻岩 ; granitic gneiss ; 铀—铅计时 ; U-Pb dating ; 天山 ; Tianshan Mountains
- 页码：p.243-252
- 图表：4 illus., 2 tables, 55 refs.
- 分类号：0802,1300
- issnNo：ISSN1000-8845
- isbnNo：CN65-1092/P
LA-ICP-MS zircon U-Pb dating and geochemical composition analysis have been applied to the granitic gneiss that intruded into Xingxingxia Group from Sangshuyuanzi in the eastern segment of the Central Tianshan. LA-ICP MS Zircon U-Pb dating of granitic gneiss gives concordant ages of （453.1±6.5） Ma, indicating that they are the products of magmatic activities of Early Ordovician. The results of 22 measuring points of zircons of the granitic gneiss show that there are no remnant of Late Precambrian zircons or age information.Combining with the feature of rock minerals,we suggest that the original rocks are intermediate-acid intrusive rocks.Geochemical analyses show that SiO2=62.45%～66.52%,K2O/Na20=l.74～1.99 and A/CNK =0.94～0.95,which indicates that the rocks are high K and peraluminous.The chondrite-nomalized REE pattern shows the enrichment of LREE, weak negative Eu anomalies,and Eu at 0.69-0.76.The granitic gneisses are rich in large ion lithophile elements （LILE）,such as Rb,Sr, Ba,K, whereas the high field strength elements （HFSE：Nb and Ta） as well as Ti and P content are depleted.Trace element discrimination indicate that the granitic gneiss have a feature of I-type granite.Analysis of tectonic setting suggests that the granitic gneiss formed in an active continental margin arc which is subduction-related.In combination with the result of LA-ICP MS zircon U-Pb dating and regional geological setting,we suggest that the original rocks of the granitic gneiss from Sangshuyuanzi is likely the record of the arc magmatic rocks in the southward subduction of the ancient ocean of the northern margin of the Central Tianshan which is represented by Gangou ophiolite.